International Programme on Chemical Safety

Basic Analytical Toxicology


Monographs - analytical and toxicological data (6.79 - 6.113)

6.79 Organochlorine pesticides

These compounds are chlorinated hydrocarbons of diverse structure. Some that may be encountered are listed in Table 31. In addition, benzene hexachloride (BHC) is a mixture of several hexachlorocyclohexane isomers.

These compounds are commonly used as insecticides in many countries, and persist in the environment. Aldrin, dieldrin and endrin (approximate acute lethal dose, 5 g in an adult) are more toxic than lindane or DDT (approximate lethal dose, 30 g).

There are no reliable simple tests for these compounds, although a qualitative analysis can be performed by thin-layer chromatography of a solvent extract of the specimen.

Qualitative test

Applicable to stomach contents and scene residues.

Reagents

1. Petroleum ether (40-60°C boiling fraction).

2. Aqueous sodium hydroxide solution (20 g/l).

3. Sodium sulfate (anhydrous).

4. Aqueous potassium permanganate (0.1 mol/l).

5. 2-Aminoethanol (ethanolamine).

6. Silver nitrate reagent. Aqueous silver nitrate (0.1 mol/l):concentrated nitric acid (relative density 1.42) (10:1).

7. Silica gel thin-layer chromatography plate (5 × 20 cm, 20 µm average particle size; see section 4.4.1).

Standards

Aldrin, lindane, dicophane and heptachlor (all 1 g/l) in methanol.

Method

1. Extract 10 ml of sample with 5 ml of petroleum ether for 5 minutes using a rotary mixer.

2. Allow to stand for 5 minutes, take off the upper, ether layer and re-extract with a second 5-ml portion of petroleum ether.

3. Combine the ether extracts and wash with 5-ml portions of:

(a) purified water;

(b) sodium hydroxide solution;

(c) purified water.

4. Filter the extract through phase-separating filter-paper into a clean tube, dry over about 5 g of sodium sulfate and evaporate to dryness under a stream of compressed air or nitrogen.

Thin-layer chromatography

1. Reconstitute the extract in 100 µl of methanol and spot 20 µl on to a column on the plate.

2. Spot 10 µl of the standard mixture on a second column.

3. Develop the chromatogram (10-cm run) using cyclohexane (saturated tank; see section 4.4.3) and allow to dry.

4. Spray the plate with potassium permanganate solution, spray lightly with 2-aminoethanol and heat (preferably in an oven) at 100°C for 20 minutes.

5. Allow to cool, spray with silver nitrate reagent and expose to ultraviolet light (254 nm) for 15 minutes.

Results

The compounds of interest give brown/black spots. Identification is by comparison with the standard chromatogram. Dieldrin and endrin are not detected under the conditions used. Approximate hRf values for the remaining compounds are as follows:

lindane 09

dicophane 26

heptachlor 34

aldrin 41

Sensitivity

Organochlorine pesticide, 2.5 mg/l (aldrin 10 mg/l).

Clinical interpretation

Features of poisoning with organochlorine pesticides include vomiting, weakness and numbness of the extremities, apprehension, excitement, diarrhoea and muscular tremor, with convulsions and respiratory depression in severe cases. Treatment is symptomatic and supportive.

6.80 Organophosphorus pesticides

This is a very large group of compounds. There are four basic structures:

where R = alkyl; X = a wide variety of structures.

An example from each group is given in Table 32. Some organophosphorus pesticides are used as herbicides and are relatively nontoxic to humans. However, most are insecticides which interfere with neurotransmission by inhibition of acetylcholinesterase. This property forms the basis of the confirmatory test described below. Organophosphorus pesticides often have a pungent smell (of garlic), and this property can be helpful in indicating the diagnosis.

Many of these compounds are hydrolysed in alkaline solution while some (for example azinphos-methyl, diazinon, and malathion) are also unstable in acid. For this reason it is important to adjust the pH of stomach contents and scene residues to about 7 prior to the analysis.

Qualitative test

Applicable to stomach contents and scene residues.

Reagents

1. Sodium bicarbonate (solid).

2. Cyclohexane:acetone:chloroform (70:25:5).

3. Acetone:tetraethylenepentamine (9:1).

4. 4-( p-Nitrobenzyl)pyridine (20 g/l) in acetone: tetraethylenepentamine (9:1).

5. Silica gel thin-layer chromatography plate (5 × 20 cm, 20 µm average particle size; see section 4.4.1).

Standards

Dimethoate, methidathion, dioxathion and chlorpyrifos (all 1 g/l) in methanol.

Method

1. If necessary, carefully adjust the pH of 10 ml of sample to about 7 by adding solid sodium bicarbonate.

2. Extract 10 ml of sample with 5 ml of methyl tertiary-butyl ether for 5 minutes using a rotary mixer.

3. Allow to stand for 5 minutes, take off the upper, ether layer and re-extract with a second 5-ml portion of methyl tertiary-butyl ether.

4. Combine the extracts, filter through phase-separating filter- paper into a clean tube and evaporate to dryness under a stream of compressed air or nitrogen.

Thin-layer chromatography

1. Reconstitute the extract in 100 µl of methanol and spot 20 µl on a column marked on the plate.

2. Spot 10 µl of the standard mixture on a second column.

3. Develop the chromatogram (10-cm run) using cyclohexane: acetone:chloroform (saturated tank, see section 4.4.3) and allow to dry.

4. Spray the plate with 4-( p-nitrobenzyl)pyridine solution and heat, preferably in an oven, at 110°C for 30 minutes.

5. Allow to cool and spray with acetone:tetraethylenepentamine (9:1).

Results

The compounds of interest give purple spots on a pale brown background. Approximate hRf values are as follows:

dimethoate 11

methidathion40

malathion 42

dioxathion 47

propetamphos49

bromophos 54

chlorpyrifos58

Sensitivity

Organophosphorus pesticide, 5 mg/l.

Confirmatory test

Applicable to plasma or serum. See cholinesterase activity monograph (section 6.30).

Results

The presence of an acetylcholinesterase inhibitor is indicated if the yellow colour in the control tube is deeper than that in the test tube. If the colour in the tube containing pralidoxime is similar to that in the control tube, this provides further confirmation that an inhibitor of acetylcholinesterase is present in the sample. Of course, other inhibitors of acetylcholinesterase, such as many carbamate pesticides, also give a positive result in this test.

Clinical interpretation

Exposure to organophosphorus insecticides may cause bronchorrhoea, respiratory distress, excessive salivation, nausea, muscle weakness and eventually paralysis. Measurement of erythrocyte cholinesterase activity (see section 3.1.5) provides a method of assessing the severity of poisoning with this group of compounds. Treatment is symptomatic and supportive, and may include the administration of atropine and pralidoxime (see Table 4).

6.81 Orphenadrine

N,N-Dimethyl-2-(2-methylbenzylhydryloxy)ethylamine; C18H23NO; relative molecular mass, 269.

Orphenadrine is an anticholinergic agent used in the treatment of parkinsonism. Up to 60% of an oral dose is excreted in urine within three days. Metabolism is by N-demethylation to give N-desmethylorphenadrine and N,N-didesmethylorphenadrine, N-oxidation to give orphenadrine N-oxide, and a number of other pathways. The fatal dose of orphenadrine in an adult is thought to be 2-4 g.

There is no simple qualitative test for orphenadrine, but it can be detected and identified by thin-layer chromatography of a basic solvent extract of urine, stomach contents or scene residues (see section 5.2.3).

Clinical interpretation

Acute orphenadrine poisoning may cause a dry mouth, nausea, vomiting, tachycardia, hyperthermia, dizziness, excitement, confusion, hallucinations and convulsions. Treatment is symptomatic and supportive.

6.82 Oxalates

Oxalates are used in bleaching and cleaning agents, metal polishes and anti-rust agents. Oxalic acid ((COOH)2Ê2H2O; relative molecular mass, 126) also occurs in several plants, the leaves of domestic rhubarb and other members of the dock family (Polygonaceae) containing a particularly high concentration. The fatal dose of oxalic acid in an adult is of the order of 10 g. Oxalic acid is also a major toxic metabolite of ethylene glycol.

Qualitative test

Applicable to urine, stomach contents and scene residues.

Reagents

1. Aqueous calcium chloride solution (100 g/l).

2. Aqueous acetic acid (300 ml/l).

3. Aqueous hydrochloric acid (2 mol/l).

Method

1. Mix 1 ml of calcium chloride solution and 2 ml of clear test solution.

2. If a precipitate forms, add 1 ml of acetic acid.

3. If the precipitate remains, isolate by centrifugation and add 1 ml of dilute hydrochloric acid.

Results

A white precipitate, insoluble in acetic acid, indicates oxalate, fluoride or sulfate. If the precipitate, once isolated, is soluble in dilute hydrochloric acid (step 3), oxalate is indicated.

Sensitivity

Oxalate, 250 mg/l.

Confirmatory tests

1. Applicable to the precipitate from the qualitative test above.

Reagents

1. Urea (solid).

2. Thiobarbituric acid (solid) ( not thiopental - see section 6.9).

Method

1. Wash the precipitate twice with purified water, wash with acetone and dry at room temperature.

2. Suspend the precipitate in 50 µl of methanol in a micro-test-tube and add about 20 mg of urea and about 200 mg of thiobarbituric acid.

3. Mix thoroughly and heat gently on a micro-burner to 140-160°C.

Results

The rapid formation of a bright orange-red product, soluble in methanol, confirms oxalate.

Sensitivity

Oxalate, 250 mg/l.

2. Applicable to stomach contents and scene residues.

Reagents

1. Concentrated ammonium hydroxide (relative density 0.88).

2. Thiobarbituric acid (solid) ( not thiopental - see section 6.9).

Method

1. Mix 50 µl of test solution with 100 µl of concentrated ammonium hydroxide in a micro-test-tube and carefully evaporate to dryness using a micro-burner.

2. Add about 200 mg of thiobarbituric acid and gently reheat to 140-160°C.

Results

The rapid formation of a bright orange-red product, soluble in methanol, confirms oxalate.

Sensitivity

Oxalate, 250 mg/l.

Clinical interpretation

In addition to irritant effects on the alimentary tract when ingested, oxalate sequesters calcium, causing hypocalcaemia, muscular twitching and eventually tetany, convulsions, flank pain, acute renal failure and cardiac arrest. The crystalluria produced may be diagnostic (section 5.2.1). Treatment is normally symptomatic and supportive.

6.83 Paracetamol

Acetaminophen; N-acetyl- p-aminophenol; C8H9NO2; relative molecular mass, 151

Paracetamol is a widely used analgesic and sometimes occurs in combination with other drugs such as dextropropoxyphene. It is a metabolite of phenacetin and of benorilate, and is itself largely metabolized by conjugation with glucuronic acid and sulfate prior to urinary excretion.

Hydrolysis of the glucuronate and sulfate conjugated with concentrated hydrochloric acid gives p-aminophenol, which can be conjugated with o-cresol to form a strongly coloured dye, thus giving a sensitive qualitative test. Protein precipitation with trichloroacetic acid and subsequent treatment with nitrous acid and spectrophotometric measurement of the nitrated derivative give a selective assay for paracetamol in plasma.

Qualitative test

Applicable to urine, stomach contents and scene residues.

Reagents

1. Concentrated hydrochloric acid (relative density 1.18)

2. Aqueous o-cresol solution (10 g/l).

3. Aqueous ammonium hydroxide solution (4 mol/l).

Method

1. Add 0.5 ml of hydrochloric acid to 0.5 ml of sample, boil for 10 minutes and cool.

2. Add 1 ml of o-cresol solution to 0.2 ml of the hydrolysate.

3. Add 2 ml of ammonium hydroxide solution and mix for 5 seconds.

Results

A strong, royal blue colour developing immediately indicates the presence of paracetamol. This test is very sensitive and will detect therapeutic dosage with paracetamol 24-48 hours later.

Only aromatic amines, such as aniline, which also give rise to p-aminophenol in urine after hydrolysis are known to interfere. Ethylenediamine (from aminophylline, for example; see section 6.105) gives a green colour in this test.

Sensitivity

p-Aminophenol, 1 mg/l.

Quantitative assay

Applicable to plasma or serum.

Reagents

1. Aqueous trichloroacetic acid (100 g/l).

2. Aqueous hydrochloric acid (6 mol/l).

3. Aqueous sodium nitrite solution (100 g/l, freshly prepared).

4. Aqueous ammonium sulfamate solution (150 g/l).

5. Aqueous sodium hydroxide solution (6 mol/l).

Standards

Prepare solutions containing paracetamol at concentrations of 0, 50, 100, 200 and 400 mg/l in blank plasma. These solutions are unstable even at 4°C and must be prepared weekly or stored at -20°C.

Method

1. Add 2 ml of trichloroacetic acid to 1 ml of sample or standard, mix and centrifuge for 5 minutes

2. In a separate tube add 1 ml of hydrochloric acid to 2 ml of sodium nitrite solution and mix. Take care - brown nitrogen dioxide fumes may be evolved.

3. Add 2.0 ml of the supernatant from step 1 to the mixture obtained in step 2, mix, and allow to stand for 2-3 minutes at room temperature.

4. Add 2 ml of ammonium sulfamate solution drop by drop to remove excess nitrous acid. Take care - vigorous frothing occurs.

5. Add 2 ml of sodium hydroxide solution, vortex-mix to remove any gas bubbles and measure the absorbance at 450 nm against a plasma blank (see section 4.5.2).

Results

Calculate the plasma paracetamol concentration by comparison with the results obtained from the standard solutions. Paracetamol metabolites do not interfere, but the method is only useful within 4-24 hours of ingestion and the limit of sensitivity (normally 50 mg/l) may be 100 mg/l or more with uraemic sera.

Salicylic acid interferes to a small extent: a salicylate concentration of 1 g/l gives an apparent paracetamol concentration of 50 mg/l. However, 4-aminosalicylic acid reacts strongly (100 mg/l gives an apparent paracetamol concentration of 320 mg/l). Levodopa also interferes, and specimens contaminated with mucous heparin or other solutions containing o-cresol preservative can give very high false readings.

Sensitivity

Paracetamol, 50 mg/l.

Clinical interpretation

Following paracetamol overdosage only mild symptoms, such as nausea and vomiting, may occur initially, but severe, possibly fatal, hepatic damage may develop within days of the ingestion. Renal damage also occurs in a proportion of patients. Treatment with methionine or acetylcysteine ( N-acetylcysteine) can protect against such damage if given within 12-15 hours of the overdose (see Table 6).

Since indicators of hepatic damage such as prothrombin time (see section 3.2.1) may only become abnormal at 12-36 hours, measurement of the plasma paracetamol concentration is important not only in establishing the diagnosis, but also in assessing the need for protective therapy (Fig. 12). However, the qualitative urine test given above should be performed if there is any suspicion that paracetamol has been ingested, especially in patients presenting 24 hours or more after ingestion.

6.84 Paraquat

1,1'-Dimethyl-4,4'-bipyridylium ion; C12H14N2; relative molecular mass, 186

Paraquat is a widely used contact herbicide and may be formulated together with the related herbicide diquat. Paraquat is often encountered as the dichloride and is extremely poisonous - the lethal dose in an adult may be as low as 4 mg/kg of body weight. Paraquat and diquat give highly coloured products with sodium dithionite, and this reaction forms the basis of the test described.

Qualitative test

Applicable to urine, stomach contents and scene residues.

Reagents

1. Sodium dithionite (solid, stored in a desiccator).

2. Aqueous ammonium hydroxide (2 mol/l).

3. Blank urine.

4. Urine specimen containing paraquat ion (10 mg/l). Take care paraquat is very toxic and may be absorbed through the skin.

Method

1. Add 0.5 ml of ammonium hydroxide solution to 1 ml of test solution, and to 1-ml portions of blank and standard urines in separate test-tubes.

2. Add about 20 mg of sodium dithionite to each tube and mix.

3. If any colour forms in the test solution, agitate in air for several minutes.

Results

A blue/blue-black colour indicates the presence of paraquat. The related herbicide diquat gives a yellow-green colour, but interference from this compound is insignificant in the presence of paraquat.

If the colour fades on continued agitation in air, paraquat/ diquat is confirmed - the original colour can be restored by adding more sodium dithionite.

Sensitivity

Paraquat, 1 mg/l.

Clinical interpretation

Ingestion of paraquat may cause a burning sensation in the mouth, oesophagus and abdomen together with ulceration of the lips, tongue and pharynx. After massive absorption of paraquat, the patient usually dies quickly from multiple organ failure. Absorption of lower doses may lead to the development of progressive pulmonary fibrosis, which ultimately causes death from respiratory failure. Myocardial and renal failure may also occur. Treatment is symptomatic and supportive. Measures to reduce absorption (by the oral administration of Fuller's earth or activated charcoal) or enhance elimination (by haemodialysis) of paraquat have not been shown to affect the outcome.

The major role of an analysis is to assess the prognosis in patients at risk from progressive pulmonary fibrosis; a strongly positive result in a urine sample obtained more than 4 hours after ingestion indicates a poor prognosis. Plasma paraquat concentrations can be measured as a prognostic guide, but reliable methods require either radioimmunoassay or high-performance liquid chromatography.

6.85 Pentachlorophenol

PCP; C6HCl5O; relative molecular mass, 266

Pentachlorophenol is widely used in wood preservatives and disinfectants, and as a contact herbicide. Pentachlorophenol uncouples oxidative phosphorylation, and poisoning can occur as a result of occupational exposure as well as ingestion. Unlike the dinitrophenol pesticides, there is no yellow staining of the skin, but pentachlorophenol has a characteristic phenolic smell and this may help the diagnosis.

Qualitative test

Applicable to stomach contents and scene residues.

Reagents

1. Aqueous sodium hydroxide solution (2 mol/l).

2. Concentrated sulfuric acid (relative density 1.83).

3. Concentrated nitric acid (relative density 1.40).

Method

1. Mix 10 ml of sample and 20 ml of n-butyl acetate for 5 minutes using a rotary mixer and centrifuge for 5 minutes.

2. Transfer the extract to a clean tube and evaporate to dryness on a boiling water-bath under a stream of compressed air or nitrogen.

3. Add 0.2 ml of concentrated nitric acid to the residue and heat the tube in the boiling water-bath for 30 seconds.

4. Cool and add 0.1 ml of the mixture to 2 ml of concentrated sulfuric acid.

5. To the remainder of the cooled mixture add 2 ml of purified water and then add sodium hydroxide solution drop by drop until the pH reaches 8 (universal indicator paper).

Results

Pentachlorophenol gives a red colour in steps 3 and 4 and a brown-violet colour in step 5. Other chlorinated phenols such as hexachlorophane also react in this test.

Sensitivity

Pentachlorophenol, 1 g/l.

Clinical interpretation

Exposure to pentachlorophenol may cause sweating, hyperpyrexia, increased respiratory rate and tachycardia. Death has occurred in severe cases. Since acute poisoning occurs commonly by skin and pulmonary absorption, the prevention of further absorption is important as well as symptomatic and supportive measures.

6.86 Peroxides

Hydrogen peroxide (H2O2) is an oxidizing agent used as a bleach and sterilizing agent in cosmetics and other household products, and in industry. It is often encountered as a relatively dilute aqueous solution (60 ml/l or "20 volume", meaning that 1 volume of liquid can release 20 volumes of oxygen), but concentrations of up to 300 ml/l ("100 volume") are used in industry.

Solid metallic peroxides such as barium peroxide (BaO2) and magnesium peroxide (MgO2) are very strong oxidizing agents. These compounds have various industrial uses and liberate hydrogen peroxide on treatment with dilute acid. Some organic peroxides are used as catalysts in the production of epoxy resins.

Qualitative test

Applicable to stomach contents and scene residues.

Reagents

1. Aqueous hydrochloric acid (2 mol/l).

2. Aqueous potassium dichromate solution (100 g/l).

3. Aqueous sulfuric acid (2 mol/l).

Method

1. If the suspect material is a solid, carefully prepare a paste (about 1 g) with water and add to 10 ml of cold dilute hydrochloric acid.

2. Add 1 ml of liquid test solution (or 1 ml of the acidified solution prepared above) to 1 ml of potassium dichromate solution, 1 ml of dilute sulfuric acid and 2 ml of diethyl ether.

3. Vortex-mix for 30 seconds and allow the phases to separate.

Results

A blue colour in the ether layer indicates the presence of hydrogen peroxide, either in the test solution or by liberation from a metal peroxide.

Sensitivity

Hydrogen peroxide, 100 mg/l.

Confirmatory test

Applicable to stomach contents and scene residues.

Reagents

1. Aqueous lead acetate solution (100 g/l).

2. Hydrogen sulfide gas (cylinder). Avoid inhalation of hydrogen sulfide - it has a strong smell of rotten eggs at low concentration and is very toxic.

Method

1. Soak a strip of filter-paper in the lead acetate solution, expose to hydrogen sulfide in a fume cupboard, and allow to dry.

2. Spot 0.1 ml of liquid test solution or 0.1 ml of the acidified solution prepared for the qualitative test on the paper.

Results

A white spot is formed on the brown-black paper if hydrogen peroxide is present owing to the oxidation of lead sulfide to sulfate.

Sensitivity

Hydrogen peroxide, 500 mg/l.

Clinical interpretation

Ingestion of hydrogen peroxide gives rise to a burning sensation in the mouth, throat and oesophagus. However, there are usually no primary systemic effects, since decomposition to water and oxygen occurs before absorption. Poisoning with metallic peroxides is very rare, but these compounds are powerful oxidizing and corrosive agents and can give rise to systemic toxicity attributable to the metallic component. Treatment is symptomatic and supportive.

6.87 Pethidine

Meperidine; ethyl 1-methyl-4-phenylpiperidine-4-carboxylate; C15H21NO2; relative molecular mass, 247

Pethidine is a narcotic analgesic. About 45% of an oral dose is metabolized by N-demethylation to norpethidine, by hydrolysis to pethidinic acid, and by a number of other pathways. Up to approximately 30% of a dose is excreted in urine as pethidine and norpethidine under acidic conditions, but only 5% is excreted as these compounds if the urine is alkaline.

There is no simple qualitative test for pethidine, but this compound and its metabolites can be detected and identified by thin- layer chromatography of a basic solvent extract of urine (see section 5.2.3).

Clinical interpretation

Acute overdosage with pethidine may give rise to pin-point pupils, hypotension, hypothermia, coma and convulsions. Death may ensue from profound respiratory depression, but fatalities are relatively rare. Naloxone rapidly reverses the central toxic effects of pethidine (see section 2.2.2).

6.88 Petroleum distillates

Petrol (gasoline) is largely a mixture of normal and branched- chain aliphatic hydrocarbons (C4-C12) with boiling points in the range 39-204°C. Paraffin (kerosene) is a higher boiling fraction. Acute poisoning with petrol usually arises from inhalation of vapour as a result of industrial accident or deliberate abuse (sniffing or ingestion). Tetraethyl lead is frequently added to petrol to prevent pre-ignition (anti-knock) and chronic organo-lead poisoning can follow long-term abuse.

There are no simple qualitative tests for petroleum distillates. However, the characteristic smell of petrol on the breath or from stomach contents (or even postmortem tissue) may help to indicate the diagnosis.

Clinical interpretation

Headache, dizziness, nausea, vomiting, confusion, tremor, disorientation, coma and cardiac arrhythmias may occur after oral ingestion of petrol or sublethal inhalation of petrol vapour. The aspiration of even small quantities of petrol may lead to chemical pneumonitis. The inhalation of high concentrations of vapour may be rapidly fatal, with acute respiratory failure or cardiorespiratory arrest.

6.89 Phenacetin

p-Ethoxyacetanilide; acetophenetidin; C10H13NO2; relative molecular mass, 179

Phenacetin was previously used as an analgesic, but long-term use was associated with nephrotoxicity. It is largely metabolized to paracetamol and thus ingestion of phenacetin can be detected in urine using the o-cresol/ammonia test on a hydrolysed urine specimen.

Qualitative test

Applicable to urine, o-Cresol/ammonia test - see paracetamol monograph (section 6.83).

Results

A strong, royal blue colour developing immediately indicates the presence of paracetamol. This test is very sensitive and will detect therapeutic dosage with phenacetin 24-48 hours later.

Only aromatic amines such as aniline, which also give rise to p-aminophenol in urine after hydrolysis, are known to interfere. Ethylenediamine (from aminophylline, for example; see section 6.105) gives a green colour in this test.

Sensitivity

p-Aminophenol, 1 mg/l.

Clinical interpretation

Acute ingestion of phenacetin can cause dizziness, euphoria, cyanosis, haemolytic anaemia, respiratory depression, and cardiorespiratory arrest. Methaemoglobinaemia is often produced and may be indicated by dark chocolate-coloured blood (see section 3.2.2). Blood methaemoglobin can be measured, but is unstable and the use of stored samples is unreliable. Although metabolized to paracetamol, phenacetin does not cause acute hepatorenal necrosis. Treatment is symptomatic and supportive.

6.90 Phenols

Phenol (hydroxybenzene; carbolic acid; C6H5OH; relative molecular mass, 94) and cresol (cresylic acid; CH3.C6H4OH; relative molecular mass, 108) are used as disinfectants and in the plastics industry. Commercial cresol is a mixture of o-, m-, and p-cresols in which the m-isomer predominates. The estimated minimum lethal dose of phenol or cresol in an adult is 1-2 g.

Both phenol and cresol are readily absorbed through the skin and via the gastrointestinal tract when ingested. They are excreted in urine mainly as glucuronide or sulfate conjugates.

Qualitative test

Applicable to urine.

Reagents

1. Folin-Ciocalteau reagent. Dissolve 100 g of sodium tungstate and 25 g of sodium molybdate in 800 ml of purified water in a 1.5-l flask. Add 50 ml of concentrated orthophosphoric acid (840-900 g/kg) and 100 ml of concentrated hydrochloric acid (relative density 1.18) and reflux for 10 hours. Cool, add 150 g of lithium sulfate, 50 ml of purified water and 0.5 ml of elemental bromine, and allow to stand for 2 hours. Boil for 15 minutes to remove excess bromine, cool, filter if necessary, and dilute to 1 litre with purified water. This solution is yellow and should be stable for 4 months if stored at 4°C. Folin- Ciocalteau reagent can also be purchased ready-made.

2. Aqueous sodium hydroxide solution (2 mol/l).

Method

1. Dilute 1 ml of Folin-Ciocalteau reagent with 2 ml of purified water and add 1 ml of urine.

2. Add 1 ml of sodium hydroxide solution and vortex-mix for 5 seconds.

Results

A blue colour indicates the presence of a phenolic compound. Halogenated phenols such as 2,4,6-trichlorophenol react less strongly than nonhalogenated phenols.

Sensitivity

Phenol, 10 mg/l.

Clinical interpretation

Phenols burn and cause depigmentation of the skin, and corrode the lips and mouth if ingested. In severe poisoning, nausea, vomiting, abdominal pain, gastric haemorrhage or perforation, metabolic acidosis, coma, hypotension and shock may occur. Death from respiratory depression may ensue. Hepatorenal failure is an additional complication, and the urine may become dark-coloured owing to the presence of free haemoglobin. Apart from skin decontamination with castor oil or olive oil, treatment is symptomatic and supportive.

6.91 Phenothiazines

These compounds are derivatives of phenothiazine, which itself is used as an anthelminthic in veterinary medicine.

Phenothiazines are widely used as antihistamines, tranquillizers, and in various psychiatric disorders. They are often extensively metabolized. Chloropromazine, for example, has over 50 metabolites in humans. The test described below is based on the reaction of many of these compounds with ferric ion under acidic conditions.

Phenothiazines are often detected during thin-layer chromatography of basic solvent extracts of urine (see section 5.2.3), but specific identification of the compound ingested may be impossible if only urine is available. Low-dose phenothiazines, such as fluphenazine, may not be detectable in urine using either method.

Some commonly encountered phenothiazines are listed in Table 33.

Qualitative test

Applicable to urine, stomach contents and scene residues.

Reagent

FPN reagent. Mix 5 ml of aqueous ferric chloride solution (50 g/l), 45 ml of aqueous perchloric acid (200 g/kg) and 50 ml of aqueous nitric acid (500 ml/l).

Method

Add 1 ml of FPN reagent to 1 ml of sample and mix for 5 seconds.

Results

Colours ranging from pink, red or orange to violet or blue may indicate the presence of phenothiazines or metabolites. Urine from patients on chronic treatment with conventional phenothiazines, such as chlorpromazine, will usually give a positive reaction.

Tricyclic antidepressants such as imipramine may also give green or blue colours. False positive reactions may be obtained in patients with phenylketonuria or hepatic impairment.

Sensitivity

Chlorpromazine, 25 mg/l.

Clinical interpretation

Features of acute poisoning with phenothiazines include drowsiness, tremor, restlessness, hyperreflexia, hypothermia, hypotension, hypoventilation, convulsions, tachycardia and cardiac arrhythmias. Phenothiazine overdosage is not normally associated with a fatal outcome, although serious poisoning with, for example, chlorpromazine has been described. Treatment is normally symptomatic and supportive.

6.92 Phenytoin

Diphenylhydantoin; 5,5-diphenylimidazolidine-2,4-dione; C15H12N2O2; relative molecular mass, 252

Phenytoin is a widely used anticonvulsant. Metabolic pathways include aromatic hydroxylation and conjugation, less than 5% of a dose being excreted unchanged in urine. The estimated minimum lethal dose in an adult is 5 g, but few fatal overdoses involving this compound alone have been reported.

There is no simple qualitative test for phenytoin, but it can be detected and identified by thin-layer chromatography of an acidic solvent extract of urine, stomach contents or scene residues (see section 5.2.3).

Clinical interpretation

Features of phenytoin poisoning include tremor, nystagmus, ataxia, coma and respiratory depression. Intravenous overdosage may be associated with cardiac toxicity. Treatment is normally symptomatic and supportive. Haemoperfusion may be of value in severe cases.

6.93 Phosphorus and phosphides

Yellow phosphorus (P) and the phosphides of zinc, aluminium and magnesium are used as rodenticides, usually as a paste containing sugar and bran.

Qualitative test

Applicable to stomach contents and scene residues.

Reagents

1. Silver nitrate solution (saturated) in methanol.

2. Aqueous lead acetate solution (100 g/l).

Method

1. Soak a strip (5 × 1 cm) of filter-paper in the silver nitrate solution and allow to dry at room temperature.

2. Soak a similar strip of filter-paper in the lead acetate solution and again dry at room temperature.

3. Place 5 ml of sample in a boiling-tube fitted with a cork with a slit cut in each side.

4. Insert the test papers into the slits, stopper the tube and heat on a water-bath at 60°C for 20 minutes.

Results

If only the silver nitrate paper is blackened then phosphorus or phosphides may be present. If both papers are blackened then sulfides may be present and the result is inconclusive.

Sensitivity

Phosphorus, 1 g/l.

Confirmatory test

Applicable to blackened silver nitrate paper from the test above.

Reagents

1. Ammonium molybdate reagent. Mix 5 g of ammonium molybdate in 100 ml of water and 35 ml of concentrated nitric acid (relative density 1.42).

2. o-Toluidine reagent. Mix 50 mg of o-toluidine and 10 ml of glacial acetic acid, diluted to 100 ml with purified water.

3. Concentrated ammonium hydroxide (relative density 0.88).

4. Powdered calcium hypochlorite.

Method

1. Place the silver nitrate paper on a glass microscope slide and cover with calcium hypochlorite.

2. Leave in a moist chamber for 15 minutes to allow oxidation of phosphide to phosphate.

3. Remove excess hypochlorite by careful washing with a small amount of purified water and dry the test paper by blotting with absorbent tissue.

4. Add 50 µl of ammonium molybdate reagent to the dried paper followed by 50 µl of o-toluidine reagent and expose the paper to ammonia fumes from concentrated ammonium hydroxide in a fume cupboard.

Results

A blue colour confirms phosphorus.

Sensitivity

Phosphorus, 1 g/l.

Clinical interpretation

Acute poisoning with yellow phosphorus gives rise to gastrointestinal corrosion, nausea and vomiting, leading to coma, hypotension and hepatorenal damage. Phosphides release phosphine (PH3) on contact with water or moist air, and this gas acts on the gastrointestinal and central nervous systems. Abdominal pain may be followed by nausea, vomiting, gross ataxia, convulsions and coma, with death, usually within 2 hours, in severe cases. Treatment is symptomatic and supportive.

6.94 Procainamide

4-Amino- N-(2-diethylaminoethyl)benzamide;C13H21N3O; relative molecular mass, 235

Procainamide is a widely used antiarrhythmic drug. The major metabolite, N-acetylprocainamide (NAPA) has similar pharmacological activity to the parent compound. Up to 80% of a dose is excreted in urine in 24 hours, some 50-60% as procainamide and about 30% as NAPA. The normal oral dose is 0.5-1 g of procainamide every 4-6 hours, but as little as 200 mg given intravenously may prove fatal.

There is no simple qualitative test for procainamide, but this compound and NAPA can be detected and identified by thin-layer chromatography of a basic solvent extract of urine (see section 5.2.3).

Clinical interpretation

Acute poisoning with procainamide may cause anorexia, nausea, vomiting, diarrhoea and cardiac arrhythmias. Rapid intravenous injection may cause hypotension, convulsions and collapse. Treatment is symptomatic and supportive.

6.95 Propan-2-ol

iso-Propanol; iso-propyl alcohol; CH3.CHOH.CH3; relative molecular mass, 60

Propan-2-ol is used in lotions for topical administration, in window and screen washers, and as a solvent for toiletries. It is also used as a vehicle for certain pharmaceutical preparations and serious iatrogenic poisoning has occurred in children. The estimated minimum fatal dose of propan-2-ol in an adult is 240 ml.

Propan-2-ol is metabolized to acetone by alcohol dehydrogenase. The qualitative test described below relies on the oxidation of propan-2-ol to acetone and subsequent detection of acetone. Note that propan-2-ol is often used as a topical antiseptic prior to venepuncture, and care must be taken to avoid contamination of the sample if poisoning with this agent is suspected.

Qualitative test

Applicable to plasma or serum.

Reagents

1. Salicylaldehyde solution (100 ml/l) in methanol.

2. Aqueous sodium hydroxide solution (300 g/l).

3. Potassium permanganate reagent. Mix 3 g of potassium permanganate, 15 ml of orthophosphoric acid (850 g/kg) and 85 ml of purified water.

4. Aqueous trichloroacetic acid solution (200 g/l).

5. Sodium bisulfite (solid).

Method

1. Add 1 ml of plasma or serum to 2 ml of trichloroacetic acid solution, vortex-mix for 30 seconds and centrifuge for 5 minutes.

2. Transfer 1 ml of the supernatant to a second tube and add 0.3 ml of potassium permanganate reagent.

3. Vortex-mix for 5 seconds and allow to stand for 10 minutes. If the pink coloration fades continue to add 0.1-ml portions of potassium permanganate reagent until the colour persists.

4. Decolorize by adding solid sodium bisulfite (about 100 mg).

5. Add 3 ml of sodium hydroxide solution and 0.1 ml of salicylaldehyde solution and vortex-mix for 5 seconds.

6. Heat in a boiling water-bath for 4 minutes and cool.

Results

A red colour indicates the presence of propan-2-ol or acetone.

Sensitivity

Propan-2-ol, 50 mg/l.

Clinical interpretation

Initial symptoms of poisoning with propan-2-ol are similar to those of ethanol and include inebriation, nausea, vomiting and abdominal pain. Serious poisoning is rare but features include haemorrhagic gastritis, coma, respiratory depression, hypothermia, renal failure, rhabdomyolysis, myoglobinuria, haemolytic anaemia and ketonuria. Treatment is supportive and may include haemodialysis in severe cases.

The half-life of acetone is much longer than that of propan-2-ol so that the later signs of poisoning observed are largely those of acetone. Acetone can be detected on the breath of patients poisoned with propan-2-ol. A simple dip-strip test for urinary acetone is available.

6.96 Propranolol

(±)-1-Isopropylamino-3-(1-naphthyloxy)propan-2-ol; C16H21NO2; relative molecular mass, 259

Propranolol is a ß-adrenoceptor-blocking agent (ß-blocker). It is given orally in the treatment of hypertension and some cardiac disorders, and has a variety of other uses. Propranolol undergoes extensive first-pass metabolism, and metabolic pathways include aromatic hydroxylation, N-dealkylation, oxidative deamination and conjugation.

There is no simple qualitative test for propranolol, but this compound and some of its metabolites may be detected and identified by thin-layer chromatography of a basic solvent extract of urine (see section 5.2.3).

Clinical interpretation

Overdosage with propranolol and other ß-blockers may cause delirium, hallucinations, bradycardia, hypotension, bronchospasm, hypoglycaemia, coma and convulsions. Death may follow low-output cardiac failure or cardiorespiratory arrest. Treatment may include the administration of atropine, glucagon and ß-agonists.

6.97 Propylene glycol

Propane-1,2-diol; CH3.CHOH.CH2OH; relative molecular mass, 76

Propylene glycol is widely used as a solvent in the pharmaceutical and food industries, usually as a 100 ml/l or 200 ml/l aqueous solution, and in veterinary practice. It has a relatively short plasma half-life (4-8 hours), and is metabolized primarily to lactic and pyruvic acids, although a large proportion (20-30%) of a dose is excreted unchanged in urine.

Propylene glycol is relatively safe in normal use, but cases of poisoning associated with its use as a vehicle for drugs or vitamins given intravenously or orally have been described. Plasma concentrations associated with serious toxicity are over 4 g/l, corresponding in adults to the administration of 100-200 ml of intravenous fluids containing 200-300 ml/l propylene glycol over a relatively short time.

There is no simple qualitative test for propylene glycol.

Clinical interpretation

Overdosage with propylene glycol may cause lactic acidosis, haemolysis, coma, convulsions and cardiorespiratory arrest. Increased plasma osmolality can be a useful but nonspecific indicator of poisoning with this compound (see section 3.1.3).

6.98 Quinine and quinidine

These compounds have the structure:

Quinine ((8S, 9R)-6'-methoxycinchonan-9-ol trihydrate; C20H24N2O2Ê3H2O; relative molecular mass, 379) is the dextrorotatory stereoisomer of quinidine ((8r, 9s)-6'- methoxycinchonan-9-ol dihydrate; C20H24N2O2Ê2H2O; relative molecular mass, 361). Commercial samples of either compound may contain up to 10% or 30% of hydroquinine or hydroquinidine, respectively.

Quinine is the major alkaloid found in the bark of various species of Cinchona and is used in the treatment of malaria. It is also used to treat night cramps and is a constituent of tonic water. The fatal dose of quinine in an adult may be as little as 8 g. Quinidine is used as an antiarrhythmic. Both compounds are extensively metabolized, largely to hydroxylated metabolites.

Qualitative test

Applicable to urine.

Reagents

1. Aqueous hydrochloric acid (2 mol/l).

2. Sodium chloride (solid).

Method

1. Add 0.1 ml of dilute hydrochloric acid to 1 ml of sample and vortex-mix for 10 seconds.

2. Examine under ultraviolet light (366 nm).

3. If fluorescence is observed, add about 1 g of sodium chloride and vortex-mix for 30 seconds.

Results

If any fluorescence observed at step 2 is due to quinine/ quinidine then it will be largely, if not completely, quenched by addition of sodium chloride.

In addition to the above, quinine and quinidine and their metabolites can be detected and identified by thin-layer chromatography of a basic solvent extract of urine (see section 5.2.3). However, care may be needed to differentiate these compounds from emetine if syrup of ipecacuanha has been used to induce vomiting (see section 2.2.1 and Table 15).

Sensitivity

Quinine or quinidine, 50 mg/l.

Clinical interpretation

Overdosage with quinine may cause nausea, vomiting, abdominal pain, diarrhoea, tinnitus, deafness, vertigo, headache, blurred vision, blindness (which may be permanent), hypotension, coma, acute renal failure and cardiorespiratory arrest. In addition to general supportive measures, repeat-dose oral activated charcoal may be used to enhance systemic elimination of quinine. The efficacy of stellate ganglion block in preventing retinal damage has not been established.

The gastrointestinal and cerebellar signs of acute quinidine poisoning are similar to those caused by quinine. However, metabolic and circulatory effects predominate, and include hypotension, hypokalaemia, hypocalcaemia, hypophosphataemia, hypomagnesaemia, metabolic acidosis, acute renal failure, coma, convulsions, cardiac arrhythmias and circulatory collapse. Treatment is largely symptomatic and supportive.

6.99 Salicylic acid and derivatives

Salicylic acid

2-Hydroxybenzoic acid; C7H6O3; relative molecular mass, 138

Salicylic acid is used topically to treat various dermatological disorders. It is the principal plasma metabolite of acetylsalicylic acid and can also arise from the metabolism of methyl salicylate and salicylamide. Salicylic acid is excreted in the urine, mostly as a conjugate with glycine (salicyluric acid).

The salicylic acid derivatives described below are commonly encountered drugs.

Acetylsalicylic acid

Aspirin; C9H8O4; relative molecular mass, 180

Acetylsalicylic acid is the most frequently used salicylic acid derivative. It is used as an analgesic and is also a metabolite of aloxiprin and benorilate. The estimated minimum lethal dose in an adult is 15 g.

Acetylsalicylic acid is rapidly metabolized by plasma esterases in vivo to salicylic acid, which is then excreted in the urine, mostly as a conjugate with glycine (salicyluric acid).

4-Aminosalicylic acid

p-Aminosalicylic acid; PAS; 4-amino-2-hydroxybenzoic acid; C7H7NO3; relative molecular mass, 151

4-aminosalicylic acid is used in the treatment of tuberculosis.

Methyl salicylate

Methyl 2-hydroxybenzoate; salicylic acid methyl ester; C8H8O3; relative molecular mass, 152

Methyl salicylate (oil of wintergreen) is a strong-smelling liquid at room temperature and is widely used in topical medicinal products. On ingestion it is more toxic than acetylsalicylic acid because it is more rapidly absorbed. Deaths have occurred in children after ingestion of as little as 4 ml; 30 ml is usually fatal in adults.

Methyl salicylate is partially metabolized to salicylic acid in vivo.

Salicylamide

2-Hydroxybenzamide; C7H7NO2; relative molecular mass, 137

Salicylamide is used as an analgesic. On hydrolysis, it forms salicylic acid.

Salicylates give a distinctive purple colour with ferric ions and this reaction forms the basis of the test described. A simple dip-strip test for salicylates based on this reaction is available.

Acetylsalicylic acid and methyl salicylate do not themselves react with ferric ions, so that stomach contents and scene residues must be hydrolysed before analysis is performed. Salicylamide is only detectable after hydrolysis, even in urine samples.

Qualitative test

Applicable to urine, stomach contents and scene residues.

Reagent

Trinder's reagent. Mix 40 g of mercuric chloride dissolved in 850 ml of purified water with 120 ml of aqueous hydrochloric acid (1 mol/l) and 40 g of hydrated ferric nitrate, and dilute to 1 litre with purified water.

Method

Add 0.1 ml of Trinder's reagent to 2 ml of sample and mix for 5 seconds.

To test for acetylsalicylic acid or methyl salicylate in stomach contents or scene residues, and to test for salicylamide in urine, stomach contents or scene residues, first boil 1 ml of sample with 1 ml of aqueous hydrochloric acid (0.1 mol/l) for 10 minutes, cool, filter if necessary, and then neutralize with 1 ml of aqueous sodium hydroxide (0.1 mol/l).

Results

A strong violet colour indicates the presence of salicylates. Azide preservatives react strongly in this test, and weak false positives can be given by urine specimens containing high concentrations of ketones (ketone bodies).

This test is sensitive and will detect therapeutic dosage with salicylic acid, acetylsalicylic acid, 4-aminosalicylic acid, methyl salicylate and salicylamide.

Sensitivity

Salicylate, 10 mg/l.

Quantitative assay

Applicable to plasma or serum (1 ml).

Reagent

Trinder's reagent (see above).

Standards

Aqueous solutions containing salicylic acid at concentrations of 0, 200, 400 and 800 mg/l. Store at 4°C when not in use.

Method

1. Add 5 ml of Trinder's reagent to 1 ml of sample or standard.

2. Vortex-mix for 30 seconds and centrifuge for 5 minutes.

3. Measure the absorbance of the supernatant at 540 nm against a plasma blank (see section 4.5.2).

Results

Calculate the plasma salicylate concentration from the graph obtained on analysis of the salicylate standards. Some salicylate metabolites interfere, but plasma concentrations of these compounds are usually low. Oxalates, for example, from fluoride/oxalate blood tubes, also interfere in this test.

Sensitivity

Salicylate, 50 mg/l.

Clinical interpretation

The topical use of salicylic acid and methyl salicylate and ingestion of salicylates may give rise to features of salicylism. Respiratory alkalosis followed by metabolic acidosis is characteristic, although in practice a mixed acid-base disturbance is usually seen. The results of blood gas analyses are an important guide to the severity of poisoning (see section 3.1.2). If acute poisoning is suspected, the plasma salicylate concentration should be measured using the method described above.

Active measures to correct acid-base status and urinary alkalinization to enhance elimination of the poison may be considered, depending on the patient's condition and the plasma salicylate concentration. Repeated oral activated charcoal may also be employed (see section 2.2.3).

Serial plasma salicylate and urine pH measurements are valuable in monitoring active treatment. A guide to the interpretation of plasma salicylate results is given in Fig. 13. Concentrations of up to 300 mg/l may be encountered during therapy in adults.

6.100 Strychnine

Strychnidin-10-one; C21H22N2O2; relative molecular mass, 334

Strychnine and the related compound brucine (10, 11- dimethoxystrychnine) are highly toxic alkaloids derived from the seeds of Strychnos nuxvomica and other Strychnos species. Strychnine has a bitter taste and is sometimes used in tonics for this reason. It is also used to exterminate rodents and other mammalian pests, and has been used to adulterate diamorphine (see section 6.73).

In addition to the simple tests given below, strychnine can be detected and differentiated from brucine by thin-layer chromatography of a basic or neutral extract of urine (see section 5.2.3).

Qualitative test

Applicable to stomach contents and scene residues.

Reagents

1. Concentrated ammonium hydroxide (relative density 0.88).

2. Ammonium vanadate (5 g/l) in concentrated sulfuric acid (relative density 1.83).

Method

1. Add 5 ml of sample to 1 ml of concentrated ammonium hydroxide and extract with 20 ml of chloroform for 10 minutes using a rotary mixer.

2. Centrifuge for 10 minutes, remove the upper, aqueous layer and transfer the solvent extract to a clean tube.

3. Evaporate the extract to dryness under a stream of compressed air or nitrogen and dissolve the residue in 100 µl of chloroform.

4. Transfer 50 µl of the reconstituted extract to a porcelain spotting tile and add 50 µl of ammonium vanadate solution.

Results

A violet colour which changes to red and then to yellow over 10 minutes suggests the presence of strychnine.

Sensitivity

Strychnine, 100 mg/l.

Confirmatory test

Applicable to stomach contents and scene residues.

Reagents

1. Granulated zinc.

2. Concentrated hydrochloric acid (relative density 1.18).

3. Aqueous sodium nitrite solution (100 g/l, freshly prepared).

Method

1. Add a granule of zinc to 1 ml of sample and 1 ml of concentrated hydrochloric acid and heat in a boiling water-bath for 10 minutes.

2. Cool, remove any remaining zinc and add 50 µl of sodium nitrite solution.

Results

Strychnine gives a pink colour.

Sensitivity

Strychnine, 10 mg/l.

Clinical interpretation

Ingestion of strychnine can cause convulsions and, notably, opisthotonos. Treatment is symptomatic and the patient may need intensive supportive care.

6.101 Sulfides

Sulfides such as sodium sulfide (Na2S) and calcium sulfide (CaS) are used in depilatory agents, luminous paints, ore dressing and flotation, dye and plastics manufacture, photography, printing, veterinary medicine and a variety of other applications. Ingested elemental sulfur is metabolized to sulfide in the gastrointestinal tract; the ingestion of 10-20 g of sulfur may cause gastrointestinal symptoms. Hydrogen sulfide is often released when metallic sulfides are treated with water or acid, and their mammalian toxicity may be related to production of this compound.

Hydrogen sulfide (H2S) is a colourless, extremely toxic gas which has, at low concentrations, an unpleasant odour of rotten eggs. At higher concentrations the olfactory response is lost and acute hydrogen sulfide poisoning is a leading cause of sudden death in the workplace. Hydrogen sulfide is released by decomposition of organic sulfur-containing materials and from sources of volcanic activity, and is used in the plastics, tanning, dye, rubber and petroleum industries, among others.

Hydrogen sulfide is rapidly metabolized in vivo by oxidation to sulfate and other pathways. Any analysis for sulfide in biological materials should be performed as quickly as possible, since the sulfide ion is unstable in such samples.

Qualitative test

Applicable to stomach contents and scene residues.

Reagents

1. Aqueous sulfuric acid (100 ml/l).

2. Lead acetate reagent. Mix 50 ml of lead acetate solution (100 g/l in boiled, purified water) and 5 ml of aqueous acetic acid (2 mol/l).

Method

1. Soak a strip of filter-paper in lead acetate reagent and allow to dry.

2. Add 3 ml of dilute sulfuric acid to 1 ml of sample, suspend the lead acetate-impregnated paper in the neck of the tube and place in a boiling water-bath in a fume cupboard.

Results

Sulfides give rise to hydrogen sulfide gas which blackens lead acetate paper.

Sensitivity

Sulfide, 50 mg/l.

There is no simple confirmatory test for sulfides; microdiffusion methods are unreliable.

Clinical interpretation

Exposure to hydrogen sulfide can give rise to headache, dizziness, drowsiness, nausea, sore throat, coma, convulsions, cardiac arrhythmias, respiratory depression and pulmonary oedema. Treatment may include the administration of 100% oxygen and nitrites.

6.102 Sulfites

Sulfites such as sodium sulfite (Na2SO3), sodium bisulfite (NaHSO3), and sodium metabisulfite (Na2S2O3) are used in the paper, water treatment, photographic and textile industries and as preservatives in beverages, foods and medications. Sulfur dioxide gas (SO2) may be liberated on contact with acid. The estimated fatal dose of sodium sulfite in an adult is 10 g.

Quantitative assay

Applicable to urine.

Reagents

1. Magenta reagent. Add 0.02 g of basic magenta (fuchsine, CI 42510) to 100 ml of aqueous hydrochloric acid (1 mol/l) and store in the dark.

2. Formaldehyde solution. Dilute 1 ml of methanol-free aqueous formaldehyde solution (340-380 g/kg) to 1 litre with purified water.

Standards

Anhydrous sodium sulfite (1.575 g) in 1 litre of purified water (to give a sulfite ion concentration of 1 g/l), diluted with purified water to give standards containing sulfite ion at concentrations of 0.5, 1.5, 3.0, 6.0 and 10.0 mg/l.

Method

1. Add 1 ml of magenta reagent and 3 ml of formaldehyde solution to 50 µl of sample.

2. Add 1 ml of magenta reagent and 3 ml of purified water to a second 50-µl portion of the sample.

3. Vortex-mix for 5 seconds and allow to stand for 5 minutes.

4. Measure the absorbance of the test solution from step 1 at 570 nm using the sample blank from step 2 as reference (see section 4.5.2).

Results

Construct a calibration graph following analysis of the standard sulfite solutions and calculate the sulfite concentration in the sample.

Sensitivity

Sulfite, 0.5 mg/l.

Clinical interpretation

Acute sulfite poisoning can cause generalized flush, faintness, syncope, wheezing, shortness of breath, cyanosis and cold skin. Urticaria and angioedema may be seen within minutes of exposure, and may be followed by acute bronchospasm and respiratory arrest in certain people. Treatment is symptomatic and supportive. The normal urinary concentration of sulfite ion is less than 6 mg/l.

6.103 Tetrachloroethylene

Perchlorethylene; tetrachloroethene; CCl2:CCl2; relative molecular mass, 166

Tetrachloroethylene is used as an anthelminthic and as a solvent in dry-cleaning and vapour degreasing. Acute poisoning with this compound is normally from massive accidental exposure or deliberate inhalation (solvent abuse). Only about 0.5% of an absorbed dose of tetrachloroethylene is metabolized to trichloroacetic acid, but this can be detected in urine using the Fujiwara test.

Qualitative test

Applicable to urine. Fujiwara test - see carbon tetrachloride monograph (section 6.23).

Results

An intense red/purple colour in the upper, pyridine layer indicates the presence of trichloro compounds. The blank analysis excludes contamination with chloroform from the laboratory atmosphere.

This test will detect ingestion or exposure to low doses of compounds that are extensively metabolized to trichloroacetic acid, such as chloral hydrate, dichloralphenazone and trichloroethylene, 12- 24 hours later. With tetrachloroethylene, the test is correspondingly less sensitive, since such a small proportion of a dose is metabolized.

Sensitivity

Trichloroacetate, 1 mg/l.

Clinical interpretation

Signs of poisoning with tetrachloroethylene include ataxia, nausea, vomiting, coma, respiratory depression and cardiac arrhythmias. Hepatorenal damage is very uncommon. Treatment is symptomatic and supportive.

6.104 Thallium

Thallium (Tl) salts are employed in the manufacture of semiconductors, pigments and lenses, and are used as rodenticides in many countries. The lethal dose of thallium in an adult is 0.2-1 g.

The test given below can be used to give an approximate measure of urinary thallium concentration if poisoning with this element is suspected.

Quantitative assay

Applicable to urine.

Reagents

1. Cyanide reagent. Dissolve 1.6 g of sodium hydroxide, 1.2 g of potassium sodium tartrate and 1.36 g of potassium cyanide in 10 ml of water. Take care when using concentrated cyanide solutions.

2. Dithizone solution (250 mg/l) in chloroform (freshly prepared).

Standards

Blank urine to which has been added a solution of thallium acetate in purified water (1.0-g/l) to give thallium ion concentrations of 0.1, 1.0, 5.0 and 10.0 mg/l.

Method

1. Add 1 ml of cyanide reagent to 5 ml of sample or standard in a 10-ml glass-stoppered test-tube and vortex-mix for 10 seconds.

2. Add 2 ml of dithizone solution, vortex-mix for 1 minute, and centrifuge for 5 minutes.

3. Discard the upper, aqueous layer and filter the chloroform extract through phase-separating filter-paper into a clean tube.

4. Measure the absorbance of the extract at 480 nm against a blank urine extract (see section 4.5.2).

Results

A pink/red colour in the lower chloroform layer indicates the presence of thallium at concentrations of 1 mg/l or more. Construct a calibration graph of absorbance against thallium concentration in the standards and measure the thallium concentration in the sample. A number of metal ions may interfere in this assay. Atomic absorption spectrophotometry is needed in order to measure thallium definitively.

Sensitivity

Thallium, 0.1 mg/l.

Clinical interpretation

Acute poisoning with thallium salts may lead to gastrointestinal stasis, while intermediate and late effects may include disturbances of the peripheral and central nervous systems, the cardiorespiratory system, eyes and skin. Scalp and facial hair loss is a typical sign of thallium poisoning. Patients with urinary thallium concentrations exceeding 0.5 mg/l should be treated with potassium ferrohexacyanoferrate (Prussian blue; see Table 6) until urinary thallium excretion is below 0.5 mg/day.

6.105 Theophylline

1,3-Dimethylxanthine; C7H8N4O2; relative molecular mass, 180 Theophylline is a bronchodilator widely used in the treatment of asthma, often as a mixture with ethylenediamine (aminophylline). Theophylline is metabolized to 3-methylxanthine, 1,3-dimethyluric acid, and 1-methuric acid; caffeine is a metabolite in neonates.

There is no simple test for theophylline applicable to biological fluids. Ethylenediamine gives a green colour in the o-cresol/ammonia urine test used to detect paracetamol, but in this case only indicates prior ingestion of aminophylline (see section 6.83).

Quantitative assay

Applicable to plasma or serum.

Reagents

1. Tris buffer (0.2 mol/l, pH 7.0). Mix 200 ml of aqueous hydrochloric acid (1 mol/l) and 214 ml of aqueous tris(hydroxymethyl)aminomethane free base (121 g/l).

2. Sodium carbonate buffer (0.1 mol/l, pH 9.0). Mix 10 ml of aqueous sodium carbonate (10.6 g/l) and 890 ml of aqueous sodium bicarbonate solution (8.4 g/l).

Standards

Solutions containing theophylline concentrations of 5, 10, 20 and 50 mg/l in blank plasma.

Method

1. Add 0.5 ml of tris buffer to 2.0 ml of sample or standard, and add 10 ml of chloroform.

2. Vortex-mix for 2 minutes, and centrifuge for 5 minutes.

3. Remove the upper, aqueous layer and filter 8 ml of the chloroform extract through phase-separating filter-paper into a clean tube.

4. Add 2.5 ml of sodium carbonate buffer to the chloroform extract, vortex-mix for 2 minutes and centrifuge for 5 minutes.

5. Transfer 2.0 ml of the aqueous extract (upper layer) to a quartz spectrophotometer cell and measure the absorbance at 280 nm against a plasma blank (see section 4.5.2).

Results

Construct a calibration graph following analysis of the standard theophylline solutions and calculate the theophylline concentration in the sample. Specimens containing a theophylline concentration of more than 50 mg/l should be diluted with blank plasma and re-analysed.

Use of the pH 9.0 extraction and measurement at 280 nm minimizes interference from barbiturates, but caffeine, theophylline metabolites and some other drugs may interfere in this assay.

Sensitivity

Theophylline, 5 mg/l.

Clinical interpretation

Acute overdosage with theophylline and other xanthines may cause palpitations, hypotension, diuresis, central nervous system stimulation, nausea, vomiting, marked hypokalaemia, metabolic acidosis and convulsions. Treatment is normally symptomatic and supportive, with particular emphasis on correcting the hypokalaemia. Repeat-dose oral activated charcoal can be used to enhance theophylline clearance (see section 2.2.3).

Plasma theophylline concentrations attained during therapy are normally less than 20 mg/l. Toxic effects are more frequent at concentrations above 30 mg/l, while plasma concentrations of 50 mg/l or more may be encountered in fatal cases.

6.106 Thiocyanates

Potassium thiocyanate (KSCN) and sodium thiocyanate (NaSCN) were previously used in the treatment of hypertension, but nowadays these compounds are used principally as synthetic intermediates, and in the printing, dye and photographic industries. Thiocyanate is a metabolite of cyanide and thiocyanate toxicity is most commonly encountered as a result of chronic sodium nitroprusside administration. Thiocyanate is also found in the blood of cigarette smokers from metabolism of cyanide. Thiocyanate is excreted in urine; the plasma half-life is about 3 days if renal function is normal.

Qualitative test

Applicable to urine, stomach contents and scene residues.

Reagent

Aqueous ferric chloride solution (50 g/l).

Method

Add 0.1 ml of ferric chloride solution to 0.1 ml of sample and mix.

Results

A deep red colour indicates the presence of thiocyanate.

Sensitivity

Thiocyanate, 50 mg/l.

Quantitative assay

Applicable to plasma or serum.

Reagents

1. Aqueous trichloroacetic acid solution (50 g/l).

2. Ferric nitrate reagent. Dissolve 80 g of ferric nitrate nona- hydrate in 250 ml of aqueous nitric acid (2 mol/l), dilute to 500 ml with purified water and filter.

Standards

Prepare aqueous solutions containing thiocyanate ion concentrations of 5, 10, 20, 50 and 100 mg/l by dilution from an aqueous solution of potassium thiocyanate (1.67 g/l, equivalent to a thiocyanate ion concentration of 1.00 g/l).

Method

1. Add 4.5 ml of trichloroacetic acid solution to 0.5 ml of sample or standard, vortex-mix for 30 seconds and centrifuge for 5 minutes.

2. In a darkened room, add 2 ml of the supernatant to 4 ml of ferric nitrate reagent, vortex-mix for 5 seconds, and measure the absorbance at 460 nm against a reagent blank (see section 4.5.2).

Results

Construct a calibration graph following analysis of the standard thiocyanate solutions and calculate the thiocyanate concentration in the sample.

Sensitivity

Thiocyanate, 2 mg/l.

Clinical interpretation

Acute ingestion of thiocyanate salts may cause disorientation, weakness, hypotension, confusion, psychotic behaviour, muscular spasm and convulsions. Treatment is normally symptomatic and supportive.

In nonsmokers, plasma thiocyanate concentrations range from 0.1 to 0.4 mg/l, while in heavy smokers concentrations typically range from 5 to 20 mg/l. Plasma thiocyanate concentrations can reach 100 mg/l during sodium nitroprusside therapy, but toxicity often occurs at concentrations above 120 mg/l. Plasma concentrations of the order of 200 mg/l have been reported in fatalities.

6.107 Tin

Metallic tin (Sn) and its inorganic salts are used in metallurgy and in tanning, polishing and metal coating ("tin" cans). Organotin compounds, usually ethyl, butyl or phenyl derivatives, such as tributyl tin, are used as pesticides, in antifouling paints on ships, and as stabilizers in plastics. Inorganic tin compounds are poorly absorbed after ingestion, but organotin derivatives are well absorbed from the gastrointestinal tract and can cause serious systemic toxicity.

There are no simple qualitative tests for either inorganic tin or organotin compounds suitable for use in the diagnosis of acute poisoning.

Clinical interpretation

Ingestion of high doses of inorganic tin compounds may cause nausea, vomiting and diarrhoea. Acute exposure to organotin derivatives may cause headache, vomiting, abdominal pain, tinnitus, deafness, loss of memory, disorientation, coma and respiratory depression. Treatment is symptomatic and supportive.

6.108 Tolbutamide

1-Butyl-3- p-tolylsulfonylurea; C12H18N2O3S; relative molecular mass, 270

Tolbutamide is a hypoglycaemic agent widely used to treat diabetes. About 85% of an oral dose is excreted in urine as the 4-carboxy and 4-hydroxymethyl metabolites; only about 5% is excreted unchanged. The normal dose of this drug is up to 3 g/day; a fatality has followed the ingestion of 50 g of tolbutamide.

There is no simple qualitative test for tolbutamide in biological specimens. However, the colorimetric procedure given below can be used to assess the severity of poisoning if overdosage is suspected. This method can also be used to measure other sulfonylurea hypoglycaemic agents, such as chlorpropamide and acetohexamide, in plasma using the appropriate standards.

Quantitative assay

Applicable to plasma or serum.

Reagents

1. Aqueous hydrochloric acid (0.02 mol/l).

2. Fluorodinitrobenzene reagent. 1-Fluoro-2,4-dinitrobenzene (1 g/l) in iso-amyl acetate, freshly prepared.

Standards

Solutions containing tolbutamide concentrations of 20, 50, 100 and 200 mg/l in blank plasma.

Method

1. Add 2.5 ml of dilute hydrochloric acid to 0.5 ml of sample or standard and add 10 ml of iso-amyl acetate.

2. Vortex-mix for 2 minutes and centrifuge for 5 minutes.

3. Transfer 6 ml of the upper, organic layer to a clean tube, add 1 ml of fluorodinitrobenzene reagent and vortex-mix for 30 seconds.

4. Place a loosely fitting glass cap on the top of the tube and heat on a boiling water-bath for 10 minutes.

5. Cool, allow to stand at room temperature for 30 minutes, and measure the absorbance at 346 nm against a plasma blank (see section 4.5.2).

Results

Construct a calibration graph following analysis of the standard tolbutamide solutions and calculate the tolbutamide concentration in the sample. Samples containing tolbutamide at concentrations above 200 mg/l should be diluted with blank plasma and re-analysed.

The chromogenic reagent used in this test reacts with most primary and secondary amines and some other functional groups. The results must therefore be interpreted with caution if other drugs may be present.

Sensitivity

Tolbutamide, 10 mg/l.

Clinical interpretation

Overdosage with sulfonylurea hypoglycaemics such as tolbutamide may cause nausea, vomiting, abdominal pain, hypotension, drowsiness, prolonged hypoglycaemia, hyperkalaemia, metabolic acidosis, coma, convulsions, pulmonary oedema and circulatory failure. Treatment includes correction of hypoglycaemia by giving glucose.

Plasma tolbutamide concentrations attained during thera py are normally 40-100 mg/l and toxicity may be expected at plasma concentrations above 200 mg/l. Measurement of blood glucose is important in establishing the diagnosis of poisoning with tolbutamide and other hypoglycaemic drugs and in monitoring treatment (see section 3.1.1).

6.109 Toluene

Methylbenzene; C6H5.CH3; relative molecular mass, 92

Toluene is used as a solvent in adhesives, paints and paint- strippers (which often also contain dichloromethane or methanol) and is widely used in industry. Acute toluene poisoning is normally from massive accidental exposure or deliberate inhalation (glue sniffing, solvent abuse). Some 80% of a dose of toluene is metabolized to benzoic acid, which is conjugated with glycine to give hippuric acid. Measurement of urinary hippurate excretion can be used as an index of chronic toluene exposure, but sodium benzoate or benzoic acid used as food preservatives are also metabolized to hippurate and results should therefore be interpreted with caution.

Quantitative assay

Applicable to urine.

Reagents

1. Aqueous hydrochloric acid (0.05 mol/l).

2. Dimethylaminobenzaldehyde reagent, p-Dimethylaminobenzaldehyde (40 g/l) in acetic anhydride containing a few crystals (about 0.5 g) of anhydrous sodium acetate.

3. Sodium chloride (solid).

4. Precipitated silica.

Standards

Blank urine, plus urine to which hippuric acid has been added to give concentrations of 0.2, 0.5, 1.0 and 2.0 g/l. All samples must be prepared from one urine specimen. These solutions are stable for 1 month if stored at 4°C in the dark.

Method

1. Adjust the pH of 1.0 ml of sample or standard to 2 with dilute hydrochloric acid, and add sodium chloride until the solution is saturated.

2. Add 2 ml of diethyl ether:methanol (9:1), vortex-mix for 1 minute and centrifuge for 5 minutes.

3. Aspirate the upper, ether layer into a clean tube and re-extract the aqueous phase with a further 2 ml of diethyl ether:methanol (9:1).

4. Combine the ethereal extracts and add 1 ml to about 0.5 g of precipitated silica in a clean tube.

5. Remove the solvent under a stream of compressed air or nitrogen, add 3 ml of dimethylaminobenzaldehyde reagent, and heat on a heating block at 135°C for 5 minutes.

6. Cool, add 4 ml of methanol, vortex-mix for 1 minute and centrifuge for 5 minutes.

7. Aspirate the methanolic extract into a clean tube and re-extract the silica with a further 4 ml of methanol.

8. Combine the methanolic extracts and measure the absorbance at 460 nm against the blank urine extract (see section 4.5.2).

Results

Prepare a calibration graph following analysis of the standard hippuric acid solutions and calculate the hippuric acid concentration in the sample. It is important to use a portion of the same urine used to prepare the standards as the blank, since hippurate excretion varies with dietary benzoate intake, as indicated above.

Sensitivity

Hippurate, 0.1 g/l.

Clinical interpretation

Features of acute toluene poisoning include ataxia, nausea, vomiting, respiratory depression, coma and cardiac arrhythmia. Hepatorenal damage is uncommon. Treatment is symptomatic and supportive.

Urinary hippuric acid concentrations are normally 0.1-0.2 g/l; concentrations greater than 1 g/l indicate prior exposure to toluene if other possible sources of benzoate can be excluded. In acute poisoning with toluene, death may supervene before hippurate excretion is raised.

6.110 1,1,1-Trichloroethane

Methylchloroform; CCl3.CH3; relative molecular mass, 133

1,1,1-Trichloroethane is widely used as a solvent for dry- cleaning and vapour degreasing, and in typewriter correction fluids. Acute poisoning with 1,1,1-trichloroethane is normally from massive accidental exposure or deliberate inhalation (solvent abuse). Some 2% of an absorbed dose of 1,1,1-trichloroethane is metabolized to 2,2,2-trichloroethanol and then to trichloroacetic acid. This can be detected in urine using the Fujiwara test.

Qualitative test

Applicable to urine. Fujiwara test - see carbon tetrachloride monograph (section 6.23).

Results

An intense red/purple colour in the upper, pyridine layer indicates the presence of trichloro compounds. The blank analysis excludes contamination with chloroform from the laboratory atmosphere.

This test is sensitive and will detect ingestion or exposure to low doses of compounds that are extensively metabolized to trichloroacetic acid, such as chloral hydrate, dichloralphenazone and trichloroethylene, 12-24 hours later. However, with 1,1,1-trichloroethane the test is correspondingly less sensitive, since such a small proportion of a dose is metabolized.

Sensitivity

Trichloroacetate, 1 mg/l.

Clinical interpretation

Signs of poisoning with 1,1,1-trichloroethane include ataxia, nausea, vomiting, coma, respiratory depression and cardiac arrhythmias. Hepatorenal damage is uncommon. Treatment is symptomatic and supportive.

6.111 Trichloroethylene

Trichloroethene; CHCl:CCl2; relative molecular mass, 131

Trichloroethylene is a well known solvent and has also been used as a general anaesthetic. Acute poisoning with trichloroethylene is normally from massive accidental exposure or deliberate inhalation (solvent abuse). As with some hypnotic drugs, including chloral hydrate and dichloralphenazone, trichloroethylene is extensively metabolized (about 80% of an absorbed dose) to trichloroacetic acid. This can be detected in urine using the Fujiwara test.

Qualitative test

Applicable to urine. Fujiwara test - see carbon tetrachloride monograph (section 6.23).

Results

An intense red/purple colour in the upper, pyridine layer indicates the presence of trichloro compounds. The blank analysis excludes contamination with chloroform from the laboratory atmosphere.

This test is very sensitive and will detect exposure to trichloroethylene 12-24 hours later. However, other compounds also give rise to trichloroacetic acid in vivo, including the chlorinated solvents 1,1,1-trichloroethane and tetrachloroethylene, and caution must be exercised in reporting results.

Sensitivity

Trichloroacetate, 1 mg/l.

Clinical interpretation

Clinical features of acute poisoning with trichloroethylene include ataxia, nausea, vomiting, coma, respiratory depression and cardiac arrhythmias. Hepatorenal damage may also occur. Treatment is symptomatic and supportive.

6.112 Verapamil

5-( N-(3,4-Dimethoxyphenethyl)- N-methylamino)-2-(3,4- dimethoxyphenyl)-2-isopropylvaleronitrile; C27H38N2O4 relative molecular mass, 455

Verapamil is used to treat hypertension. Metabolic pathways include N-dealkylation ( N-demethylation gives norverapamil which is pharmacologically active) with O-demethylation and conjugation of the resulting compounds. About 70% of a dose is excreted in urine, 10% as norverapamil, and less than 5% as the parent compound.

There is no simple qualitative test for verapamil, but this compound and its metabolites can be detected and identified by thin- layer chromatography of a basic solvent extract of urine (see section 5.2.3).

Clinical interpretation

Acute ingestion of verapamil may cause bradycardia, hypotension, cardiac arrhythmia, metabolic acidosis, hyperglycaemia, coma and gastrointestinal haemorrhage. Treatment is supportive, and may include the administration of calcium salts and inotropic agents in severe cases.

6.113 Zinc

Zinc (Zn) is used in some alloys (brass), in metal plating (galvanizing) and in many other applications. Finely divided zinc chloride (ZnCl2) is produced by chemical smoke generators and this compound is also used in soldering flux, dry battery cells and dental cement. Zinc oxide (ZnO) is used in making pharmaceuticals (zinc oxide plaster), rubber and white pigments. The acute oral toxicity of compounds like zinc chloride is limited since they are powerful emetics. Fatalities have been reported after the intravenous administration of 7.4 g of zinc and the inhalation of zinc chloride fumes.

There is no simple qualitative or quantitative test for zinc in biological specimens.

Clinical interpretation

Acute poisoning with zinc compounds may cause fever, nausea, vomiting, diarrhoea, lethargy, muscle aches, weakness, cyanosis, pulmonary oedema, acute pancreatitis and acute renal failure. Treatment is symptomatic and supportive.