Toxicological analysis

DEFINITION: Methodologies used to identify and quantify the presence of drugs (including alcohol) and toxins in samples and to interpret the significance of the results.

SIGNIFICANCE: In forensic science, toxicological analysis encompasses aspects of sample preparation, chemical analysis, and interpretation of results. Toxicology plays a vital role in a wide range of different case types encountered in forensic work, including death investigations (criminal or otherwise), impaired driving, sexual assault, and drug use in sports or in other matters involving questions about human performance.

Toxicology departments are among the busiest in most forensic laboratories, owing to the pervasiveness of drug and alcohol use and the potential for the involvement of these substances in a wide range of case types. Toxicological analysis may be performed on a variety of sample types, including materials of biological and nonbiological origin. Typical biological samples include blood, urine, visceral tissues (such as tissues from the liver), stomach contents, hair, and saliva. Nonbiological samples may include portions of food and/or beverages, syringes, and other items. The analysis may be qualitative (for example, simple identification of the presence of a substance within a sample) or quantitative, where the amount or concentration of a toxin contained within the sample is important for toxicological interpretation.

Procedures

After properly collected, handled, and documented samples are obtained and submitted to the laboratory, toxicological analysis often occurs in four distinct phases. The first stage involves consideration of the circumstances of the case and any requests for particular analyses from the submitting agencies (coroner or medical examiner, agencies). In this step, details about particular symptomatology or events that occurred in the case provide some guidance for the toxicologist in deciding which drugs or toxins to analyze for, which sample types are suitable (pending availability) for analysis, and which methods to use.

Next, samples generally undergo some form of preparation to remove residual impurities prior to chemical analysis, given the chemical complexity of samples typically encountered in forensic work (such as decomposed tissues). This sample preparation process typically involves some combination of homogenization, dilution, and selective extraction of the compounds of interest from the background material into a pure solvent. Extraction generally involves manipulation of the chemical conditions (such as pH, solvent, or temperature) to favor diffusion of drugs or toxins from the sample matrix into another phase. For example, acidic drugs may be ionized as a result of proton loss at elevated pH values.

Extraction may then first require a reduction of pH in a blood sample, ensuring that the acidic drug remains uncharged and therefore more soluble in an organic solvent that is immiscible (incapable of mixing) with the blood. Adding such a solvent to a blood sample creates two phases: an aqueous blood phase and an organic phase. Shaking this mixture results in diffusion of the drug into the organic phase, leaving many of the blood constituents in the aqueous phase. Similar approaches may be used to isolate basic compounds or neutral (that is, neither acidic nor basic) compounds.

Multiple extraction cycles may be performed on the same sample, or multiple, different extraction steps may be performed in series in an effort to create the “cleanest” extract possible. In many cases, extracts are then concentrated through evaporation of the extraction solvent to improve the sensitivity of detection in the subsequent analysis step.

Analysis of prepared samples then generally occurs by instrumental methods, including spectrophotometry, gas chromatography, liquid and mass spectrometry. It should be noted that, despite even the best sample preparation efforts, prepared extracts still usually contain multiple chemical compounds. Consequently, most instrumental analyses used in toxicological analysis include some sort of separation of the constituents of the extract mixture (for example, through gas or liquid chromatography). Forensic scientists may use these methodologies qualitatively, quantitatively, or in combination to provide as much information about the chemical makeup of extracts as possible.

In 2024, Dr. Diane Moore used funding from the National Institute of Justice to develop a new method of postmortem toxicological analysis. This method utilized liquid chromatography tandem mass spectrometry in addition to the traditionally-utilized gas chromatography-mass spectrometry. This new procedure allows for faster, large-scale blood sample screening methods, potentially allowing toxicology labs to process samples in a faster and more efficient manner.

Interpretation of Results

After all the analyses of a given extract have been conducted and have been thoroughly reviewed for scientific completeness, the analytical results are collected and interpreted collectively for their toxicological significance. Here, important considerations include drug concentrations, the sample type in which they were measured (that is, a given drug concentration in a blood sample may have toxicological implications that are different from the implications for the same concentration in a urine sample), any potential drug interactions (such as the combination of alcohol and other depressant drugs), and the circumstances of the case, including any special considerations (such as the stability of a given drug under a particular set of storage conditions). Generally, the toxicologist must conduct a thorough review of the scientific literature to assess the effects of different drugs at different concentrations and under different circumstances.

After the four phases of analysis are complete, the toxicologist prepares a report detailing which samples were analyzed, the analytical findings, and the methods by which the results were obtained. This report also contains the toxicologist’s conclusions and statements regarding sample handling, continuity of evidence, and chain of custody. The scientist may then be called upon to provide as an and further questioned about the contents of the report.

Bibliography

Baselt, Randall C. Disposition of Drugs and Chemicals in Man. 7th ed. Foster City, Calif.: Biomedical Publications, 2004.

‗‗‗‗‗‗‗. Drug Effects on Psychomotor Performance. Foster City, Calif.: Biomedical Publications, 2001.

Brunton, Laurence L., John S. Lazo, and Keith L. Parker, eds. Goodman and Gilman’s the Pharmacological Basis of Therapeutics. 11th ed. New York: McGraw-Hill, 2006.

Karch, Steven B., ed. Drug Abuse Handbook. 2d ed. Boca Raton, Fla.: CRC Press, 2007.

Levine, Barry, ed. Principles of Forensic Toxicology. 2d ed., rev. Washington, D.C.: American Association for Clinical Chemistry, 2006.

"New Screening Method to Detect Drugs and Poisons Postmortem." National Institute of Justice, 11 June 2024, nij.ojp.gov/topics/articles/new-screening-method-detect-drugs-and-poisons-postmortem. Accessed 18 Aug. 2024.

Rygaard, Karen, et al. "Overview of Systematic Toxicological Analysis Strategies and Their Coverage of Substances in Forensic Toxicology." Analytical Science Advances, 15 Apr. 2023, doi.org/10.1002/ansa.202200062. Accessed 18 Aug. 2024.