Analyzing the effect of preservatives on the stability of cocaine and its metabolite, benzoylecgonine, in fixed postmortem rat tissues after chronic cocaine administration using LC/MS/MS
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Abstract
The stability of drugs in postmortem tissues and preservative solutions is important information for forensic toxicologists and pathologists to understand when investigating a death. In this study, postmortem tissues (liver, heart, lung, kidney, and muscle) were obtained from rats who chronically self-administered cocaine. They were stored using four preservation techniques: 10% formalin solution, paraformaldehyde perfusion, 2% sodium fluoride solution, and fresh at −20°C. Tissue samples were tested at one week and one month storage durations for each preservation technique, and in parallel, the analytes in the two preservative solutions (10% formalin and 2% sodium fluoride) also were quantified. All tissue samples were homogenized, extracted using the solid-phase extraction method, and analyzed for cocaine and benzoylecgonine concentrations using the QSight® LX-50 UHPLC in tandem with QSight® 220 CR Laminar Flow Triple Quadrupole Mass Spectrometer.
Both cocaine and benzoylecgonine were detected in tissue samples and preservative solutions. Two percent sodium fluoride was an effective preservation technique for tissues stored long-term, however, the −20°C samples consistently had the second highest average concentrations for both analytes, thus making it a more steady preservation technique. Despite duration of storage, muscle specimens resulted in the highest average cocaine concentrations across all preservation techniques, averaging 1.622 ng/mL at one week and 4.319 ng/mL at one month.
Liver specimens were stable for long-term storage with a higher long-term average detection and quantitation of benzoylecgonine in those samples. More leaching of cocaine from tissues occurred in 10% formalin solutions, while more leaching of benzoylecgonine occurred in 2% sodium fluoride solutions. Because toxicology results vary depending on the preservation technique, tissue type, and duration of storage, it is important to consider these variables when evaluating cocaine and benzoylecgonine testing results.