Quantitative screening for benzodiazepines in blood by dual-column gas chromatography and comparison of the results with urine immunoassay.

A dual-column retention index method is described for quantitative gas chromatographic (GC) screening of 26 benzodiazepine drugs and metabolites in the blood using DB-5 and DB-17 capillary columns and electron capture detection. The method involves a one-step, small-scale liquid-liquid extraction with ethyl acetate and derivatization with N-methyl-N-(tert-butyldimethylsilyl)trifluoroacetamide with 1% tert-butyldimethylsilyl chloride. The results from the GC screening of 514 postmortem blood samples were compared to those obtained from urine immunoassay (Syva ETSplus with a 200-ng/mL cutoff). Both methods gave a negative result in 284 cases and a positive result in 149 cases. In 48 cases, urine was negative by immunoassay but blood was positive by GC. The opposite situation (blood negative, urine positive) was detected only in four cases. In 29 cases, an invalid result was obtained by urine by immunoassay: 26 blood samples of those cases were negative and three samples positive by GC. In postmortem forensic toxicology, the present GC method seems to be a good alternative to the common combination of urinary immunoassay followed by quantitative analysis of blood by chromatography.