Authors Christine Moore, Cynthia Coulter, and Katherine Crompton Immunalysis Corporation 829 Towne Center Drive Pomona, CA 91767 USA For contact purposes only: Michael Zumwalt Agilent Technologies, Inc. 9780 S. Meridian Blvd Englewood, CO 80112 USA Abstract An analytical procedure for the determination of phencycli- dine in oral fluid has been developed and validated using liquid chromatography with tandem mass spectral detec- tion, following initial screening with enzyme-linked immunosorbent assay. The oral fluid samples were col- lected using the Quantisal™ device, and any drugs present were quantified using mixed mode solid-phase extraction followed by mass spectrometric detection in positive atmospheric pressure chemical ionization mode. For con- firmation, two transitions were monitored and one ratio determined, which had to be within 20% of that of the known calibration standard. The monitoring of the qualify- ing transition and requirement for its presence within a specific ratio to the primary ion has the potential of limiting the sensitivity of the assay. However, the additional confi- dence in the final result as well as forensic defensibility Detection of Phencyclidine in Human Oral Fluid Using Solid Phase Extraction and Liquid Chromatography with Tandem Mass Spectrometric Detection Application were considered to be of greater importance. The limit of quantitation was 5 ng/mL; the intraday precision of the assay was 3.04% (n = 5); interday precision was 3.35% (n = 5). The percentage recovery of phencyclidine from the oral fluid collection pad was 81.7 % (n = 6). The methods were applied to both proficiency specimens and to sam- ples obtained during research studies in the USA. Introduction Oral fluid is increasing in popularity as an alterna- tive matrix to blood or urine for standard drug testing due to its ease of collection, difficulty of adulteration, and the improving sensitivity of ana- lytical techniques. Phencyclidine (PCP) is included in the proposed United States federal regulations for saliva drug testing in the workplace, and the suggested cut-off concentration is 10 ng/mL of neat oral fluid. Surprisingly, there are no pub- lished procedures for the determination of PCP in oral fluid using liquid chromatography with tandem mass spectrometry (LC/MS/MS). However, there is one method for its analysis in rat plasma [1]. Other methods for the determination of PCP in blood [2], urine [3], hair [4], and meconium [5] have been reported, which incorporate the more standard gas chromatography-mass spectrometry instrumentation. There are publications describing the analysis of various other drugs of abuse in oral fluid using LC/MS/MS in APCI mode, in a similar manner to our approach; however, many of these procedures monitor only one transition in the multiple- reaction monitoring mode (MRM). Recently, Forensics