Method validation of drugs of abuse using microchip capillary electrophoresis-mass spectrometry
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Drugs of Abuse (DOAs) are among the single largest contributor to crime in the United States and present a high cost to society in terms of financial costs and physical/mental well-being of individuals. The forensic community requires a variety of validated methods to detect and analyze DOAs in a variety of different sample types, and most developed methods utilize a liquid or gas chromatography (GC or LC) separation system paired to a mass spectrometer (MS) detection detector. Capillary Electrophoresis (CE) based separation techniques have also been experimented with due to this technique’s high efficiency and speed, high resolving power, low sample consumption, and potentially lower cost when compared to GC or LC based techniques, even though the sensitivity of these systems is perceived to be weaker. The goal of this research to develop a CE-MS/MS method utilizing the ZipChipTM to demonstrate it can accurately and reliably detect and quantify DOAs. The DOAs analyzed for this method were opioids and benzodiazepines, and these were 6-monacetylmorphine, 7-aminoclonazepam, codeine, diazepam, dihydrocodeine, 2-Ethylidene-1,5-dimethyl-3,3-diphenylpyrrolidine fentanyl, heroin, hydrocodone, hydromorphone, meperidine, methadone, morphine, norfentanyl, oxycodone, and oxymorphone. Standard Practices for Method Validation in Forensic Toxicology guidelines from the Academy Standards Board (ASB) of Toxicology were used as the template for this validation; samples were prepared and analyzed as neat standards in diluent, blood and urine were assessed for interferences, ionization suppression/enhancement, and extraction recovery. The total runtime for the method was 3.5 minutes, with the retention time range being 1.4 to 2.9 minutes. All samples were prepared using compound standards diluted in metabolite diluent, which consisted of methanol, ammonium acetate, and water prior to injection. The calibration curves consisted of eight calibrator samples that ranged from 0.5 ng/ml to 200 ng/ml for all analytes, and a linear model was used for each compound. The minimum acceptable 𝑅2 value was set to >0.98, and each curve had a weighing factor of 1𝑥2. Each curve for most of the compounds achieved the minimum requirement apart from two Codeine curves (0.9781 and 0.9785) and 7-aminoclonazepam (0.9791). Bias and precision were assessed at three concentrations- 5, 100, and 150 ng/ml. The minimum requirement for bias and precision for a compound was if the percent bias or coefficient of variation was within +/- 20%. Most compounds in this method exhibit acceptable levels of bias (except for Dihydrocodeine which had a bias of 24.58% at 100 ng/ml), and the only compounds to meet the minimum requirement for precision were 6-MAM, 7-aminoclonazepam, diazepam, fentanyl, methadone, and morphine. The limit of detection and limit of quantitation were both set at the lowest calibrator level of 0.5 ng/ml, and no carryover was observed in this method. No interferences occurred due to both deuterated internal standards and from common compounds such as benzylecogine, cocaine, and lidocaine, but blood cause signal interference with fentanyl and urine caused signal interference with methadone and norfentanyl. Ionization suppression and enhancement was observed for a majority of the compounds, and this observation will need to be assessed as to the effect it has on validation parameters in the future. The results collected suggest that accurate, reliable, and sensitive data may be collected if a compound has a specifically paired deuterated internal standard included in the sample. The speed of the suggested method and the minimal sample preparation could be desirable for forensic use. Further testing will need to be conducted to fully validate this method for blood and urine.