Stability of phencyclidine in stored blood samples

A retrospective study was conducted to determine the stability of phencyclidine (PCP) in whole blood samples stored for 1-3 years at both 4°C and -20°C. The PCP concentrations of these samples were initially determined in 1993, 1994, or 1995, then stored until 1996, when the PCP concentrations were determined again. All quantitations of PCP were by means of gas chromatography-mass spectrometry using the internal standard method. PCP was extracted from the blood by solid-phase extraction followed by liquid-liquid back extraction. The method of quantitation for reanalysis was identical to that used in the initial PCP analyses. The results of this study reveal a tendency for the concentrations of PCP to decrease gradually over a period of 3 years. Samples stored for 1 year did not show a significant change in PCP concentration, whereas samples stored for 2 years showed a 9.6% average decrease, and samples stored for 3 years showed a 17.9% average decrease. Following storage, PCP was present in all samples in which it had been originally detected. The results of this study indicate that PCP, at the concentrations in this study, remains sufficiently stable to be detected within 3 years of storage at 4°C and -20°C.