Phencyclidine has been analyzed in a variety of biological specimens, the most common of which are urine and blood or serum. Air, saliva, sweat, vitreous fluid, solid organ tissues fingernails, and meconium have also proved to be amenable to analysis for PCP. Phencyclidine was analyzed in human hair as early as the mid-1970s, and hair has been shown to be a useful record of long-term PCP exposure. Most routine analysis detects only un-metabolized PCP, although many metabolites are readily detectable and could be included in an analytical scheme if desired).
Phencyclidine exists in human tissues mostly as an unconjugated organic base and can be isolated from aqueous solution by liquid-liquid extraction after alkalination. Solid-phase extraction using cation exchange resins is also routinely used. Because most analytical procedures for PCP are designed to look for the parent compound, and the parent doesn’t form glucuronide or sulfate corrugates, no hydrolysis is required.
Screening analyses for PCP can be roughly divided into 2 groups based on the underlying analytical principle. Most laboratories, which screen large numbers of specimens, use systems based on one of several immunoassay techniques. When high throughput is not required, chromatographic techniques are frequently used.
Immunoassay analytical systems rely on the competitive binding of labeled and unlabeled drug to an antibody to that drug. There are many variations on this basic principle and most manufacturers have a commercially available assay for PCP. Among these are radioimmunoassay (RIA), enzyme-multiplied immunoassay (EMIT) enzyme-linked immunoassay (ELISA), fluorescence polarization immunoassay (FPIA), cloned enzyme donor immunoassay (CEDIA), and kinetic interaction of micro-particles in solution (KlMS). A more recently developed approach called up-converting phosphor technology has also been used to detect phencyclidine.
There are also quite a few assay systems that were designed for use “onsite,” and are based on a color change similar to a home pregnancy test. Immunoassay techniques are inexpensive, quick, sensitive, and easily adapted to automation. One disadvantage is the possibility of cross-reacting substances giving false positive results. For example, dextromethorphan in urine has produced false-positive immunoassay PCP results. The antidepressant agent venlafaxine has been responsible for several false-positives in immunoassay testing systems, as has the synthetic Opoid analgesic tramadol. Ibuprofen and metamizol have been shown to have cross-reactions of 0.00006% and 0.00005%, respectively, with some immunoassay systems. Although these cross-reactions are low, they have been shown to be significant in overdose situations.
All immunoassay results should be confirmed by a specific method, such as GC-MS.
Chromatographic methods used to screen specimens for PCP include thin-layer chromatography ~C}, high-pressure liquid chromatography (HPLC), gas-liquid chromatography (GLC) with flame-ionization detection (FID), GC with nitrogen-phosphorus detection (NPD), and GC-MS. TLC can analyze several samples at a time, but suffers from a lack of sensitivity and is quite labor-intensive. The other chromatographic methods are sensitive and adaptable to automation, but are capable of running only 1 sample at a time, resulting in lower throughput.
A number of newer screening methods are currently under investigation. An immunoassay with capillary electrophoretic separation has been described. Also being evaluated are a GC separation with surface ionization detection, capillary electrophoresis with laser-reduced fluorescence, and a GC separation after headspace-solid phase micro-extraction (HS-SPME).
Almost all confirmation methods for the identification of drugs involve one of the several forms of mass spectrometry. The standard over the years has been TIC coupled to electron impact quadruple mass spectrometry. This technique is the one commonly referred to when the abbreviation GC-MS is used. Mass spectral analysis in both the selected ion monitoring basilar and full-scan modes is used. Ion-trap MS has been used to confirm the presence of many of the common drugs including PCP in urine, as well as PCP in hair. Mass spectrometry has recently been shown to be capable of detecting phencyclidine in nails and umbilical cord tissue. High pressure liquid chromatography (HPLC or LC) coupled to MS detectors, a technique known as LC-MS, has also been used to detect PCP and its metabolites in urine, blood, and meconium. An expansion of this technique, LC-MS-MS, has also been used to detect and quant are PCP and its metabolites in urine and serum. Direct probe analysis, in which the specimen is inserted directly into the MS ion source. Without passing through a chromatographic separation step, has also been reported. Chemical ionization (CI), surface ionization, and tandem MS (MS-MS) procedures have been successfully used to increase the sensitivity of the analyses.
Analytical Considerations and Troubleshooting
In the screening of PCP by immunoassay methods, potential cross reactivity with dextromethorphan, venlafaxine and ibuprofen should be noted.
The most common method of testing for PCP involves a confirmation of the parent drug in the urine. Since 5 to 20% of the drug is excreted in the urine unchanged, this is an adequate approach. The preferred internal standard for the analysis is phencyclidine-d5, a deuterated analog in which the hydrogen atoms on the phenyl ring have been replaced with deuterium atoms. This internal standard is available from a number of suppliers, including Sigma-Aldrich and Cerriliant.
When PCP is analyzed by Go, the Rector temperature should be no higher than 200 °C to prevent the pyrolysis of a portion of the PCP to 1 -phenyl- 1 – cyclohexene .
Neither the CAP Forensic Urine Drug Testing (FUDT) program nor the Society of Hair Testing (SoHT) specifies cutoff values for Phencyclidine at this time. According to the Mandatory Guidelines for Federal Workplace Drug Testing Programs as originally published in 1994 and then updated, the screening and confirmation cutoffs for Phencyclidine in urine are both 25 ng/mL. The suggested cutoffs for hair are 300pg/mg, for oral fluid is 10ng/mL, and for sweat are 20ng/patch. In all cases the screening and confirmation cutoffs for a given specimen are the same.