Direct and LC analysis of five benzodiazepines in human urine plasma usingan ADS restricted access extraction column

An alkyl-diol-silica (ADS) precolumn was used for the direct and on-line ex traction of several benzodiazepines from serum and urine. The protein compo nent of the biological sample was flushed through the ADS column, while sim ultaneously extracting the benzodiazepine compounds in the pores of the ADS stationary phase, The role of hydrophobic interactions in the extraction m echanism was confirmed. Column switching was employed to elute the extracte d analytes from the ADS column into a high-performance liquid chromatograph y reverse-phase C18 column for the isocratic separation and UV detection of the benzodiazepines. Sample preconcentration via large volume injections w as possible, improving the limits of detection. The calculated clonazepam, oxazepam, temazepam, nordazepam and diazepam detection limits were 38.8, 24 .2, 31.7, 31.3, 45.0 ng/ml in serum, respectively, and 48.4, 24.5, 31.7, 33 .1, 52.9 ng/ml for urine, respectively. The method was linear over the rang e of 50-10000 ng/ml in both matrices with an average linear coefficient (R- 2) value of 0.9918. The injection repeatability and intra-assay precision o f the method were evaluated over ten injections, resulting in a percent rel ative standard deviation < 5%. The ADS extraction column was robust, provid ing many direct injections of biological fluids for the extraction and subs equent determination of benzodiazepines. (C) 2001 Elsevier Science B.V. All rights reserved.