Drugs of Abuse, Analysis of
Authors: Dasgupta Amitava 
Published: September 2006

Alcohol is the most widely abused legal drug in the USA. Other widely abused illegal drugs are amphetamines, cocaine, cannabinoids, opiates, barbiturates, benzodiazepines, methadone, methoqualone and phencyclidine (PCP). Lysergic acid diethylamide (LSD), a popular drug in 1960, is coming back to the illegal market. Drug testing in the USA is either mandatory or nonmandatory. In the first group, an employer is required by federal regulation to test. Urine is the preferred specimen, although blood and gastric content are useful in detecting drugs in the case of an acute recent overdose. Screening of abused drugs by immunoassay has certain limitations. For example, several legal drugs used in over‐the‐counter cold medications contain phenylpropanolamine, ephedrine or pseudoephedrine. These drugs can cause positive results in amphetamine immunoassays because of their structural similarity to methamphetamine. Moreover, in the gas chromatography/mass spectrometry (GC/MS) confirmation of amphetamine and methamphetamine, if the temperature of the injector port is over 185°C, ephedrine and pseudoephedrine can be dehydrated to methamphetamine, resulting in a false positive result. Alcohol levels in blood can be measured by either immunoassay or gas chromatography (GC). Many clinical toxicology laboratories use immunoassay for measuring blood alcohol because it is automated, speedy and a simple technique. False positive alcohol concentration may result from high concentrations of lactate dehydrogenase (LDH) (lactic acidosis) and lactate in a specimen.

However, this interference can be eliminated by measuring alcohol concentration in the protein‐free ultrafiltrate. Alcohol is not bound to serum protein and appears in the ultrafiltrate. On the other hand, LDH has a molecular weight of 180 000 and is absent in the ultrafiltrate. GC is the method of choice for measuring legal blood alcohol.

Immunoassay screening tests provide only preliminary results. Moreover, a negative immunoassay result does not mean that no drug was present. It may indicate that the concentration of drug was below the cutoff limit. Guidelines have been developed by the Department of Health and Human Services (DHHS) for drug testing.

People try to beat drug testing by adding a variety of compounds such as salt, lemon juice, household bleach and Visine eye drops to their urine. Therefore it is important to check sample integrity (temperature, pH, specific gravity). True positive results from ingestion of poppy seed cake (contains opiates), health inca tea (contains cocaine) or hemp seed oil (contains tetrahydrocannabinol (THC)) in drug testing have been reported. Confirmation of the abused drug is essential to follow up screening tests and should be done using a different analytical technique. GC/MS is considered the gold standard for the confirmation of abused drugs in biological fluids and tissue specimens. The pre‐analytical steps include extraction of the drug from urine or serum matrix using an organic solvent followed by derivatization. The common derivatizing agents are trifluoroacetic anhydride, pentafluoropropionic anhydride, heptafluorobutyric anhydride, methanolic sulfuric acid, N‐O‐bis(trimethylsilyl) trifluoroacetamide (BSTFA) etc. New derivatization techniques have appeared in the literature for GC/MS confirmation of abused drugs. The perfluorooctanoyl and 4‐carbethoxyhexafluorobutyryl derivatives of amphetamines are less volatile than traditional fluoro derivatives, have higher molecular weights and are more useful for unambiguous identification. Propyl chloroformate and very recently 2,2,2‐trichloroethyl chloroformate have been introduced as new derivatization reagents for amphetamines.

Another challenge in testing drugs of abuse is the identification of designer drugs, which are usually derivatives of known drugs. Usually, screening test results using immunoassays are negative if designer drugs are present. For example, phenmetrazine at concentrations up to 6000 ng mL−1in urine would be tested negative by the EMIT (Enzyme Multiplied Immunoassay Technique, Behring Diagnostics, San Jose, CA). Recently γ‐hydroxybutyric acid (GABA) has been reported as a date rape drug. This drug can be identified in blood and urine using high‐performance liquid chromatography/mass spectrometry (HPLC/MS).

Hair analysis is becoming popular owing to the long‐term deposition of many abused drugs in hair. However, the analytical challenges are greater as the concentrations are low. This is especially true for Δ9‐THC and LSD where the sensitivity of a bench model GC/MS is not sufficient for analysis.