Direct Automated EMIT® d.a.u. Analysis of N,N-Dimethylformamide-Modified Serum, Plasma, and Postmortem Blood for Benzodiazepines, Benzoylecgonine, Cannabinoids, and Opiates*

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Abstract
Serum, plasma, and postmortem blood treated with two volumes of N,N-dimethylformamide (DMF) and centrifuged, were directly analyzable by means of the EMIT d.a.u. reagents on the Syva Autocarousel in the same manner as urine. Cutoff values in milligrams (immunochemically cross-reactive analyte equivalents)/L are 0.05 for morphine (MOR), 0.15 for benzoylecgonine (BZE), 0.20 for oxazepam (OX), and 0.02 for 11-nor-Δ9-tetrahydrocannabinol carboxylic acid (THCC). The relationship of concentrations (µg/mL serum) to absorbance changes (ΔA) were S-shaped up to > 3.0 for MOR, 4.0 for BZE, > 5.0 for OX, and 0.2 for THCC. Beyond these maximal concentrations, ΔA values declined. Thus, negatives should be repeated on substantially diluted aliquots to avoid missing extraordinarily high positives. “False” quantitative negative/positive noncongruence between total EMIT cross-reactives and free-drug analyses by gas chromatography/mass spectrometry (GC/MS) were 0/17 (N = 75) for opiates, 8/0 (N = 119) for cocaine products, and 19/5 (N = 103) for cannabinoids. For benzodiazepines (N = 58) the “false” negative/“false” positive ratio of EMIT (total)/high performance liquid chromatography (HPLC) (free) was 4/4. Within-day precision as coefficient of variation (CV) of quantitative estimates was 8–18%. For between-day precision, quantitative estimates varied by 8% for MOR, 15% for BZE, 18% for OX, and 34% for THCC.