A rapid and sensitive method for simultaneous screening, quantification and confirmation of 17 barbiturates in horse plasma using liquid chromatography-tandem mass spectrometry is described. Analytes were recovered from plasma by liquid-liquid extraction using methyl tert-butyl ether, separated on a C18 column, and analyzed in negative electrospray ionization mode. Multiple-reaction monitoring was employed for screening and quantification. Confirmation for the presence of the analytes was achieved by comparing ion intensity ratio. The ranges for limits of detection, quantification and confirmation were 0.003-1 ng/mL (S/N ≥ 3), 0.01-2.5 ng/mL and 0.02-5 ng/mL, respectively. The linear dynamic range of the method was 0.1-100 ng/mL. The precision and accuracy at 0.5, 5 and 50 ng/mL of all 17 barbiturates during intra-day assay were 1.6-8.6% and 96-106%, respectively. For inter-day assay, precision and accuracy at the same three concentrations were 2.6-8.9% and 96-106%, respectively. Analysis of all 17 analytes was completed within 7 min. Thus, the present method is fast, simple, sensitive and reproducibly reliable.
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