What steps should be employed by a toxicologist in an analytical scheme to look for barbituates in a urine sample? What chemicals or instrumentation should be used at each step?

Question

What will be an ideal response?

Answer 1

Answer should include points such as the following:
When establishing an analytical scheme to detect and identify drugs, the first task of a forensic toxicologist is to remove and isolate drugs and other toxic agents from the biological materials submitted as evidence. Screening and confirmation tests are then used to identify the isolated drug or drugs:
• First by controlling the acidity or basicity of a water solution into which the urine is dissolved, the toxicologist can control the type of drug that will be recovered. Barbituates are acidic drugs. Acid drugs are easily extracted from an acidified water solution with an organic solvent such as chloroform.
• Second, a screening test gives quick insight into the likelihood that a specimen contains a drug substance. It allows a toxicologist to examine a large number of specimens within a short period of time for a wide range of drugs. The three most widely used screening tests are thin-layer chromatography (TLC), gas chromatography (GC), and immunoassay.
• Third, a confirmation test identifies a specific drug or drugs. Gas chromatography/mass spectrometry is generally accepted as the confirmation test of choice.