Forensic Toxicology and Chemical Analysis Questions and Answers

Answer: D

Sodium and potassium hydroxide are strongly corrosive for all three reasons given. They dissolve proteins of the tissue, they turn fats into soap by saponification, and they draw water out of tissues. Together these produce deep, soft, slippery burns.

Since each single statement is true, the first three options are each only part of the cause, and the right answer is 'All of above'.

Answer: D

For carbon monoxide poisoning blood is kept with no preservative, according to the key. The sample is collected in a container filled to the top and tightly stoppered, so that the carboxyhaemoglobin is not changed.

Sodium fluoride is the usual preservative for blood alcohol and many other poisons, and it is therefore the tempting alternative. Sodium chloride and sodium carbonate are not used as blood preservatives for toxicology, so they are rejected.

Answer: D

Free sulphuric acid is rarely found in the stomach contents in acid poisoning because every cause listed can remove it. The acid may be vomited out, may be neutralised by alkalis given as antidotes, and may combine chemically with the tissue it touches, which is a corrosive action.

The three reasons are each true. Therefore the answer is 'All the above', and an option naming just one of them is incomplete.

Answer: D

LSD is derived from Claviceps purpurea, the ergot fungus which grows on rye and other grain. Lysergic acid from the ergot is converted into lysergic acid diethylamide.

Cannabis gives hashish and marijuana, Papaver somniferum gives opium and its alkaloids, and Erythroxylum gives cocaine. None of the three is a source of LSD. The drug is made semi-synthetically, not extracted from the fungus in finished form, and this explains why forensic chemists link it to the ergot alkaloids and to lysergic acid as the starting material.

Answer: A

Poison acts most rapidly when inhaled in the gaseous state. The lungs have a very large surface and rich blood supply, and the gas passes into the blood directly and reaches the brain without going through the liver. Injection into a muscle (B) and under the skin (C) acts more slowly, because the poison has to be absorbed from the tissue, and absorption through the skin (D) is the slowest of the routes. So A is correct.

Answer: B

Aconitine is a cardiac poison (a-iii), cannabinoid is a deliriant (b-iv), brucine acts on the spinal cord and is a spinal poison, printed spiral (c-i), and calotropin is an irritant (d-ii). That gives a-iii, b-iv, c-i, d-ii, option B. Option A puts calotropin with cardiac poisons and brucine with irritants. Options C and D also pair at least two classes with the wrong poison, for example the irritant class with aconitine.

Answer: A

The active component of the marking nut (Semecarpus anacardium) is semecarpol, a phenolic oil found in the pericarp of the nut which causes blisters on the skin and is used in marking cloth. Semicarpine, semicarbine and semicarmine are not the names of its active principle. So A is correct. The nut is the fruit of a tree found in India and is also called bhilawa. Its juice is black and has been used for marking linen by washermen, which is how it gets the name. Because the juice blisters the skin, it is a plant irritant poison of forensic interest, and poisoning by it can occur by contact with the skin or after swallowing the nut.

Answer: A

The confirmatory test for phenol among the options is Ware's nitrite test. The Cobalt thiocyanate test is the Scott test for cocaine, Vitali's test is used for atropine and the other tropane alkaloids, and the Marquis test is the colour test for opiates and amphetamines. Since the other three are tests for other drugs, the answer is A. The Marquis reagent is formaldehyde in sulphuric acid and gives colours with opiates and amphetamines, and Vitali's test is a reaction of the tropane alkaloids with fuming nitric acid and alcoholic potash. Because each of the other three has a different target substance, the nitrite test is the one that goes with phenol.

Answer: D

The key gives D, all of the above. Rectified spirit, which is ethyl alcohol of about 95 per cent, cannot be used as a preservative when the poison is alcohol itself because the poison would be added to the specimen and cannot then be told from the preservative, and the key also takes phosphorus and acetic acid as poisons for which it is unsuitable. The question therefore treats all three as cases in which rectified spirit is contra-indicated, and the answer is D.

Answer: A

The official key gives ethyl alcohol as the substance estimated by the Kozelka and Hine method. I could not confirm the history of the method from a source, so the key is followed.

The other options are drugs that are estimated by other methods: opium by morphine assays, cocaine by chromatography or titration, and cannabis by chromatographic estimation of cannabinoids. The key takes none of them for this method.