Forensic Toxicology and Chemical Analysis Questions and Answers

Answer: B

A speedball is cocaine combined with DAM, diacetylmorphine, that is, heroin.

Users inject or snort the two together so that the stimulant effect of cocaine and the depressant, opioid effect of heroin are felt at once. The combination is notorious for fatal overdoses, because the cocaine masks the respiratory depression of the heroin until it wears off.

6-MAM (6-monoacetylmorphine) is the metabolite of heroin used to prove heroin use in toxicology, not the drug that is mixed. Δ⁹-THC is the active principle of cannabis, and LSD is a hallucinogen; neither forms a speedball.

Answer: D

The drug is Ketamine.

Ketamine is a dissociative anaesthetic used in human and veterinary medicine. At sub-anaesthetic doses it produces dream-like, out-of-body and hallucinatory experiences (the 'K-hole'), which made it a popular club drug, alongside MDMA and GHB, in the dance and rave scene. Its anaesthetic and amnesic effects have also led to its misuse in drug-facilitated sexual assault.

Heroin is an opioid sedative, cocaine a stimulant, and diazepam a benzodiazepine tranquilliser. All are abused, but none is valued for a psychedelic effect, which is what the question asks about.

Answer: B

The reagent is Marquis reagent.

Marquis reagent is formaldehyde in concentrated sulfuric acid. It is a colour test for drugs: opiates such as morphine and heroin give a purple to violet colour, and amphetamines an orange-brown, which makes it one of the standard screening tests.

Mandelin's reagent is ammonium vanadate in sulfuric acid. Duquenois reagent is vanillin and acetaldehyde in ethanol, used for cannabis. Zwikker's reagent is cobalt nitrate with pyridine (or a similar base), used for barbiturates. None of them is made from formaldehyde and sulfuric acid.

Answer: A

Δ⁹-THC gives a violet colour with Duquenois reagent.

In the Duquenois-Levine test, the suspected cannabis is treated with Duquenois reagent (vanillin and acetaldehyde in ethanol) and then concentrated hydrochloric acid. Cannabinoids develop a blue-violet to purple colour. Chloroform is then added; if the violet colour moves into the chloroform layer, the result is taken as positive for cannabis.

Red, pink and orange are not the cannabinoid response. Other plant materials may give coloured products, but they do not pass the violet colour into the chloroform layer, which is the point of the Levine step.

Answer: B

Cherry red blood is seen in cyanide poisoning.

Cyanide blocks cytochrome oxidase, so tissues cannot use the oxygen delivered to them. Venous blood stays rich in oxyhaemoglobin and looks bright red, giving the cherry red colour of blood and post-mortem staining. (Carbon monoxide poisoning gives a similar cherry pink colour through carboxyhaemoglobin, but it is not among the options.)

Nitrate and nitrite poisoning produce methaemoglobin, which turns blood chocolate brown. Lead poisoning causes anaemia and a blue gum line, not red blood, and sulphite does not cause a cherry red colour.

Answer: B

The key's answer is that alcohol is highly lipid soluble.

Ethanol is a small, uncharged molecule that mixes with water and also dissolves well enough in lipids to pass straight through cell membranes by passive diffusion. It therefore needs no digestion or carrier and is absorbed rapidly, about a fifth from the stomach and most of the rest from the duodenum and small intestine, reaching peak blood levels within about 30-90 minutes.

Volatility and flammability are physical properties that have nothing to do with absorption, and addictiveness is an effect on the brain, not the reason it is absorbed quickly.

Answer: D

The base is scopine.

Hyoscine (scopolamine), an alkaloid of Datura and Hyoscyamus, is the ester of tropic acid with scopine, an epoxide derivative of tropine. Atropine (racemic hyoscyamine) is the ester of tropic acid with tropine, so the two alkaloids differ only in their base.

Atropine is itself an ester, not the base. Tropine is the base of atropine, not of hyoscine, and an oxime is a class of compounds (used as cholinesterase reactivators such as pralidoxime), not this base.

Answer: A

The reaction gives an orange colour, as the key has it.

Cyanogen bromide is the reagent of the Konig reaction. It opens the pyridine ring of nicotine, and the product couples with an aromatic amine such as aniline to give a yellow to orange colour; the intensity of the yellow colour is used to measure nicotine in tobacco. Orange is the keyed shade and is the closest of the four options to that yellow-orange product. The exact shade named in a standard forensic text could not be confirmed, so the explanation rests on the reaction and on the key.

Blue, green and black are not colours that the Konig reaction of nicotine is known for.

Answer: B

The key gives a half-life of about 24 hrs.

Chlorpyrifos is an organophosphate insecticide. After absorption it is metabolised in the liver to its active oxon and to 3,5,6-trichloro-2-pyridinol (TCP), which is excreted in urine. Studies of human volunteers have found an elimination half-life of roughly a day (about 27 hours), which is the value the key takes.

12 hours is too short, and 48 and 72 hours are too long for this elimination from the body. Much longer half-lives quoted for chlorpyrifos, weeks to months, refer to its persistence in soil, not in the body.

Answer: A

Blood doping falls under enhancement of oxygen transfer.

The WADA Prohibited List places the use of autologous, homologous or heterologous blood or red blood cell products in its first prohibited method, M1, which earlier editions titled 'Enhancement of Oxygen Transfer' and later editions 'Manipulation of Blood and Blood Components'. Raising the red cell mass increases the blood's oxygen-carrying capacity, which is the aim of blood doping.

Chemical and physical manipulation (M2) covers tampering with samples and improper intravenous infusions, gene doping (M3) the misuse of genes and cells, and anabolic agents are a class of prohibited substances (S1), not a method.