Samples submitted to the laboratory are tested for the presence of drugs in all driving cases where drug use is suspected. Currently the toxicology section analyzes approximately 5,000 cases annually in Sacramento County.
The confirmation of each drug in toxicological samples is performed using a two step process. First, the sample is screened using a method called enzyme linked immunoassay (ELISA) in order to narrow down the potential classes of drugs present in the sample. ELISA is a presumptive test, meaning it is not an identification of specific drugs. When a sample has a positive screen result for any of the major drug classes, additional testing is performed to confirm the presence of any drugs causing the positive test. This technique will be replaced in 2020 by time of flight mass spectrometry, which specifically identifies drugs in each sample using high resolution mass detection.
Prior to confirmation, a sample will undergo an extraction process that is specific to the drug class(es) present in the drug screen results. This isolates the compounds of interest from the biological matrix and prepares the sample for the next instrumentation method.
The instrumental methods utilized by the laboratory to confirm the presence of drugs are called gas chromatography mass spectrometry (GCMS) and liquid chromatography mass spectrometry (LCMS). The extracted sample is injected onto a column, which is a very long, thin coiled tube. The sample is pushed through the column by a mobile phase (either liquid or gas) and the components of interest will separate from one another as they travel the length of the column. This separation occurs based on how the different compounds interact with both the mobile phase, and the interior of the column. The time it takes each compound to travel the length of column and exit is known as the retention time. After the compounds are separated, they are identified and quantified using mass spectrometry. A mass spectrometer ionizes the compounds and causes them to fragment in a manner that is specific to each individual compound. The resulting ion spectrum is essentially a chemical fingerprint, which may be compared to a reference spectrum that has been previously analyzed and catalogued. Combining this data with the retention time of a compound allows for identification.
Laboratory toxicologists routinely perform these types of analyses and testify to their findings in court. Toxicologists may also testify to the effects of these different drugs on the human body.