Forensic Toxicology and Chemical Analysis Questions and Answers

Answer: C

Wet digestion with acid breaks down the organic matter of viscera and leaves the metal ions in solution, so it is used for extracting toxic heavy metals such as arsenic, lead and mercury. Alkaloids, pesticides and barbiturates are organic compounds that would be destroyed by this treatment, and they are extracted by solvents instead, as in the Stas-Otto method.

Answer: A

Heroin (diacetylmorphine) is prepared from morphine by acetylation, and acetic anhydride is the usual acetylating reagent. Sodium hydroxide, ammonium hydroxide and calcium hydroxide are bases used in extracting or precipitating morphine (for example from opium), not for adding acetyl groups. So acetic anhydride is the correct choice.

Answer: A

Ethanol is absorbed into the blood mainly from the stomach (about a fifth) and the small intestine (the rest), the small intestine being the faster site because of its large surface. The liver is where it is metabolised, and the large intestine and kidney are not significant sites of absorption. So stomach and small intestine is the correct pair.

Answer: D

Pyrethrins come from chrysanthemum flowers, rotenone from the roots of derris and lonchocarpus, and nicotine from tobacco, so all three are insecticides of vegetable origin. Chlordane is a synthetic organochlorine insecticide made in the laboratory, so it is the one that is not of vegetable origin. It is therefore the answer.

Answer: D

The correct matching is a-iii, b-iv, c-i, d-ii. Mandelin's reagent (ammonium vanadate in sulphuric acid) is used for strychnine from Nux vomica. Marquis's reagent (formaldehyde in sulphuric acid) gives a purple colour with opium alkaloids such as morphine. The Vitali test is the test for the tropane alkaloids of Datura. The gold chloride test is used for aconite. Option A gives Marquis to Nux vomica and option B and C each shift at least two pairs wrongly, so option D is the one that matches all four.

Answer: A

Wet digestion is used to extract arsenic from viscera. Metallic poisons such as arsenic, mercury and lead are bound in the organic tissue, so the viscera are destroyed with acids (for example nitric acid and sulphuric acid) to free the metal in solution. Alkaloids and pesticides are extracted by organic solvents (Stas-Otto and similar methods), and ethanol is volatile and is recovered by distillation. Option A is correct.

Answer: B

Vitali's test is not a test for morphine. It is a test for tropane alkaloids such as atropine and hyoscyamine from Datura: nitric acid and then alcoholic potash give a violet colour. The other three are standard tests for morphine: Marquis's reagent gives purple, Frohde's reagent (sodium molybdate in sulphuric acid) gives violet turning green, and Husemann's reagent (sulphuric acid with a trace of nitric acid or formalin) gives a colour reaction. Option B is correct.

Answer: D

The poisons recovered from the alcoholic extract of the viscera are croton and curare, so (a) and (d) are true. Croton oil and curare are vegetable poisons soluble in alcohol, which is why alcohol extraction is used for them. Oxalate and copper are inorganic: oxalate is recovered from an aqueous acid extract and copper by acid digestion of the tissue, not from the alcoholic extract. Hence (b) and (c) are wrong, and option D is the answer.

Answer: D

The spinal cord is preserved in cases of strychnine poisoning. Strychnine acts on the spinal cord, causing convulsions, so the cord is the organ in which the poison's action is looked for, and it is preserved for analysis together with the usual viscera. For alcohol, arsenic and oleander the viscera such as the stomach, liver, kidney and blood are the samples of choice, and the cord is not needed. Option D is correct.

Answer: C

The time that a drug takes for its concentration in the body to fall to half is the half life period, option (C), the time constant of elimination used to say how long a drug stays in the body and how often it should be given. Full life, sleep life and quarter life are not terms of pharmacokinetics, so (A), (B) and (D) are wrong. After each half life the drug falls by half again, so after about five half lives most of it has been cleared from the body.