Fast gradient elution reversed-phase liquid chromatography with diode-array detection as a high-throughput screening method for drugs of abuse. II. Data analysis

Requirements for bioanalytical procedures in postmortem toxicology

The application of analytical techniques in postmortem toxicology is often more difficult than in other forms of forensic toxicology owing to the variable and often degraded nature of the specimens and the diverse range of specimens available for analysis. Consequently, analysts must ensure that all methods are fully validated for the particular postmortem specimen(s) used. Collection of specimens must be standardized to minimize site-to-site variability and should if available include a peripheral blood sample and at least one other specimen. Urine and vitreous humor are good specimens to complement blood. In some circumstances solid tissues such as liver are recommended as well as gastric contents. Substance-screening techniques are the most important element since they will determine the range of substances that were targeted in the investigation and provide initial indication of the possible role of substances in the death. While immunoassay techniques are still commonly used for the most common drugs-of-abuse, chromatographic screening methods are required for general unknown testing. These are still predominately gas chromatography (GC) based using nitrogen/phosphorous detection and/or mass spectrometry (MS) detection, although some laboratories are now using time-of-flight MS or liquid chromatography (LC)-MS(MS) to cover a sometimes more limited range of substances. It is recommended that laboratories include a second chromatographic method to provide coverage of acidic and other substances not readily covered by a GC-based screen when extracts do not include all physiochemical types. This may include a gradient high-performance liquid chromatography (HPLC) photodiode array method, or better LC-MS(MS). Substance-specific techniques (e.g., benzodiazepines, opiates) providing a second form of identification (confirmation) are now divided between GC-MS(MS) and LC-MS(MS) procedures. LC-MS(MS) has taken over from many methods for the more polar compounds previously used in HPLC or in GC methods requiring derivatization. Analysts using LC-MS will need to obtain clean extracts to avoid poor and variable sensitivity caused by background suppression of the signal. Isolation techniques in postmortem toxicology tend to favor liquid extraction; however solid-phase extraction and solid-phase microextraction methods are available for many analytes.

Fast gradient elution reversed-phase high-performance liquid chromatography with diode-array detection as a high-throughput screening method for drugs of abuse. I. Chromatographic conditions

A new approach for the high-throughput screening of biological samples to detect the presence of regulated intoxicants has been developed by modifying a conventional gradient elution high-performance liquid chromatograph (HPLC). The goal of this work was to improve the speed of gradient elution screening methods over current approaches by optimizing the operational parameters of both the column and the instrument without compromising the reproducibility of the retention times, which is the basis for the identification of intoxicant compounds. Most importantly, the novel instrument configuration substantially reduces the time needed to re-equilibrate the column between consecutive gradient runs, thereby reducing the total time for each analysis. The total analysis time for each gradient elution run is only 2.80 min, including 0.30 min for column re-equilibration between analyses. Retention times of standard calibration solutes are reproducible to better than 0.002 min in consecutive runs. A corrected retention index was adopted to account for day-to-day and column-to-column variations in retention time. For a set of forty-seven target compounds, the discriminating power and mean list length were found to be 0.95 and 3.26, respectively. In comparison to previous work with similar numbers of target compounds, the current approach provides an order of magnitude improvement in analysis time, and a four-fold decrease in mean list length.