Forensic Toxicology and Chemical Analysis Questions and Answers

Answer: A

Screening tests are performed for tentative identification, option A. A screening test, such as a colour test or a thin layer chromatogram, is quick and simple and shows that a substance may be present, but it is not specific, so a confirmatory test is needed. Definite identification (B) requires a specific method such as mass spectrometry, and quantitative (C) and semiquantitative (D) analyses measure the amount of the substance, which a screening test does not do. Examples of screening tests in a toxicology laboratory include the colour tests, thin layer chromatography and immunoassay kits, which are followed by gas chromatography with mass spectrometry for confirmation.

Answer: A

The Stas-Otto process is used for the extraction of poisons, option A. It is a method of extracting alkaloids and other organic poisons from viscera by alcohol and acid, then shaking out with ether at different pH values, devised by Stas and modified by Otto. It is not a method of extracting DNA (B), antigens (C) or complement (D). Stas published the method in 1851 for the detection of nicotine in the case of a murder, and it was modified by Otto in 1856.

Answer: A

The active principle of Abrus precatorius, the rosary pea or gunja, is abrin, option A. Abrin is a toxic protein, a phytotoxin, found in the seeds, and it is among the most poisonous plant substances. The other names, adbrin, abrinine and abricodine in options B, C and D, are not the principle responsible for its toxicity. The seeds of Abrus precatorius are small, glossy and red with a black spot, and they are used as jewellers' weights in India, which explains the common name gunja.

Answer: D

In a case of poisoning of a living person, the vomit, the excreta and the stomach wash are preserved for analysis, but unsoiled clothing is not, so the exception is option D. The vomit and stomach wash show what the person has taken, and the faeces and urine show what has been excreted. Clothes are kept only when they are stained with the poison or with body fluids, and clean clothing has no value as evidence.

Answer: A

Blood alcohol concentration is expressed as weight per volume percent, for example 0.08 g of alcohol per 100 mL of blood, which is 0.08 per cent w/v. This is the form used in legal limits.

Volume per volume and weight per weight are other ways of expressing concentration but they are not the standard for BAC, so "all of the above" is wrong. For example, a driving limit of 30 mg per 100 mL is the same as 0.03 per cent weight by volume, and laboratories report results in this form for court use.

Answer: B

Heroin is easily told apart from its cutting agents such as caffeine, paracetamol and sugars by thin layer chromatography, because each substance travels a different distance and gives a different Rf value on the plate.

Colour and spot tests are only presumptive and give the same reaction for many opiates. UV-Vis spectra of mixtures overlap, and IR of a mixture shows the sum of the components, which makes it hard to separate heroin from the diluents.

Answer: C

Both statements are correct. In sulphuric acid poisoning free acid is rarely found in the stomach contents, because the patient vomits much of it and any acid left is neutralised by the alkalies (such as magnesia or soda) given as antidotes, and the stomach tissue itself also reacts with it. The reason therefore explains the assertion.

The options that call either statement incorrect are wrong.

Answer: B

The picric acid test of urine detects creatinine. In alkaline solution creatinine reacts with picric acid to give an orange-red colour (the Jaffe reaction), which is the basis of the test.

Albumin is tested with heat or acid precipitation, uric acid with the phosphotungstic reagent, and chlorides with silver nitrate, so they are not detected by picric acid. The result is read as an orange colour whose depth is proportional to the creatinine present, and the test is routinely used to measure the amount of creatinine excreted in urine.

Answer: C

Nicotine is a volatile alkaloid, so when the biological material is made alkaline it can be separated by distillation (steam distillation) and collected in the distillate. Dry ashing and wet digestion destroy organic matter and are used for metallic poisons, and sublimation is used for compounds that pass from solid to vapour directly. Distillation is the method suited to nicotine from an alkaline solution.

Answer: B

The delta-9 THC content rises in the order bhang, ganja, charas and charas oil, which is (ii), (iii), (i), (iv). Bhang is made of leaves and has the least, ganja is made from the flowering tops, charas is the resin, and charas oil (hashish oil) is a concentrated extract with the most. The options that begin with charas oil or that place charas below ganja reverse the order.