Assessment of Δ9-THC and Δ9-THCCOOH bias, precision, and ionization suppression/enhancement between solid tissue...

Liquid chromatography-triple quadrupole mass spectrometry (LC-MS-MS) assays are frequently utilized for screening and confirmatory purposes in the forensic toxicology laboratory. While these techniques are excellent for the targeted identification and quantitation of a wide variety of drug classes, validation and determining fit-for-purpose is a significant requirement for each method. In the USA, the American National Standards Institute and Academy Standards Board first edition of Standard 036 currently serves as a primary resource in forensic toxicology method validation and mandates that laboratories evaluate critical performance characteristics to help ensure the production of forensically defensible results. Due to the variability of specimen quality frequently encountered in the discipline of postmortem toxicology, the State of Maryland Office of the Chief Medical Examiner Forensic Toxicology Laboratory routinely analyzes solid tissue specimens as part of the medicolegal death investigation process and evaluates liver as a representative solid tissue matrix during method validation. Authentic postmortem specimens (e.g. liver, kidney, skeletal muscle, and spleen) were used to investigate the effects of analyzing solid tissue homogenate versus solid tissue supernatant on bias, precision, and ionization suppression/enhancement of Δ9-THC and Δ9-THCCOOH. Bias was <20% for Δ9-THC and Δ9-THCCOOH in liver homogenate and supernatant with a single exception of the low QC concentration for Δ9-THC in liver homogenate (-29%). Within-run and between-run CV was <20% for Δ9-THC and Δ9-THCCOOH in liver homogenate and supernatant. Δ9-THC and Δ9-THC-d3 exhibited significant ion suppression in both liver homogenate and supernatant, while Δ9-THCCOOH and Δ9-THCCOOH-d3 showed both ion suppression and enhancement in these matrices. Noticeable quantitative differences were observed in authentic postmortem solid tissue homogenate and supernatant specimens despite evaluating identical tissue samplings. A brief discussion of the results is presented using a validated LC-MS-MS method for the confirmation and quantitation of Δ9-THC and Δ9-THCCOOH in postmortem casework.