Gcms Confirmation Procedures

Confirmation of screening results by an acceptable second method is required for SAMHSA-regulated drug testing and is recommended practice for all forensic applications. To date, GC/MS is the most frequently used confirmation procedure for the detection of amphetamine, methamphetamine, and other related compounds. Federally mandated testing currently includes confirmation cutoffs of 500 ng/mL for both amphetamine and methamphetamine, but a proposal by the SAMHSA to lower these levels to 250 ng/mL for confirmation (including MDMA, MDA, and MDEA = 3,4-methylenedioxy-N-ethylamphetamine) is in the final stages of the regulatory process (4). Current regulations also require that in order to report a sample positive for methamphetamine the metabolite amphetamine must be detected at a confirmation cutoff of 200 ng/mL.

Amphetamine and related compounds are volatile and may be lost during the evaporation step of extraction or during analysis if preventative measures are not undertaken. Procedures to reduce/eliminate loss of amphetamines include lowering the temperature for evaporation, performing incomplete evaporation or adding methanolic HCl prior to evaporation in order to produce more stable hydrochloride salts (29,37,38). GC/MS procedures for amphetamines include a derivatization step for many reasons including decreasing volatility, improving chromatography and quantitation, and forming higher molecular weight fragments yielding different mass ions and ion ratios than potentially interfering compounds (1,29,38,39). Derivatives used for amphetamines analysis include heptafluorobutyric anhydride (HFBA), pentafluoropropionic anhydride (PFPA), trifluoroacetic anhydride, 4-carboxyhexafluorobutyryl chloride (4-CB), N-methyl-N-t-butyldimethylsilyl trifluoroacetamide, N-trifluoroacetyl-1-prolyl chloride (TPC), 2,2,2-trichloroethyl chloroformate, and propylchloroformate (38-42). HFBA and PFPA are two of the more commonly used derivatives in forensic drug testing labs (1). Most procedures utilize selected ion monitoring and deuterated internal standards (IS) that have similar fragmentation patterns and almost identical chromato-graphic properties to the non-deuterated compounds. Ideally the IS concentration is the cutoff concentration, but higher concentrations may be used to extend the linearity of the assay. If higher concentrations of IS are used, the analyst should be aware of the potential impact of small amounts of non-deuterated compound present in the IS preparation (43). Monitoring the relative IS abundance of every sample and establishing acceptable limits (such as a requirement to be >50% and <200% of the calibrator IS area) is a recommended quality assurance measure (43).

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