Can gas chromatography be used in determining various opiates injested?

Answer 1

Yes, but only after the sample has been purified and concentrated.

Sample Preparation Process And Other Related Information:

Identification of a specific opiates is not as simple of just injecting a sample of stomach contents, blood, or urine into a GC (gas chromatography). Blood, stomach contents, and even urine samples would need to be "worked up" first by being filtered and/or centrifuged. The filtrate would then be added to a sepratory funnel along with ether, methylene chloride, or another appropriate organic solvent, and the pH of the aqueous fraction would be adjusted to approximately 10 to 11 in order to ensure that the drug is in its free base form rather than as a salt or bound to a protein. At that point, the drug would be tens, but usually hundreds if not thousands of times more soluble in the organic solvent and when shaken, the vast majority of the drug dissolves in the water-insoluble organic solvent. Any water is removed from the solvent, then most of the solvent is evaporated off to concentrate any analyte present before the solution is injected into a GC, although a GC coupled with a mass spectrometer (MS) is almost always used. Some opiates or opiate agonists may first need to be derivitized to an ether or ester in order to significantly reduce the melting point of the derivitized drug before it is introduced into the GC. The GC would have a heated injection port for such relatively large molecules, and it's important that the analyte is not pyrolyzed or oxidized upon being injected into the instrument.

Many closely related opiates such as codeine, morphine, and diacetylmorphine (heroin) yield a common metabolite when they are metabolized by the liver. That means that once any of those drugs has been in someone's system for longer than a certain amount of time, depending on the drug, the dosage, and the individual, it is no longer possible to tell which drug was taken initially. However, if an opiate or a combination of opiates is recovered from a person's stomach, or if a blood sample is taken before an opiate or mixture of opiates has had time to be completely or nearly completely metabolized, then it is possible to identify the individual drug or drugs taken. I have observed a drug-testing laboratory at a nuclear power plant where workers' urine was analyzed by GC/MS to identify "opiates" as well as amphetamines, cocaine, PCP, THC, and barbituates. Most companies also test for benzodiazepines like Valium® or Ativan®.

Drug-testing laboratories employed to screen employees, parolees, criminal suspects, or other subjects are not research facilities, meaning that very specific procedures are used to identify whether a drug and/or one or more of its metabolites are present in a urine [usually] or blood sample above a prescribed level. Such laboratories report a sample as "positive" or "negative" for a given drug or class of drugs; the specific drug a subject used (except for marijuana and PCP) is not identified.

Other opiates and opiate agonists (drugs that aren't technically opiates, but that bind to the same receptor sites as true opiates) have unique metabolites such that the parent molecule can be identified. Such identifications are much more likely to be performed in a forensic laboratory. A typical, drug-testing laboratory identifies a sample as "positive" or "negative" for a drug or class of drugs. The specific opiate, barbituate, benzodiazepine, or amphetamine taken is usually not identified.