Assay of omeprazole and omeprazole sulfone by semi-microcolumn liquid chromatography with mixed-function precolumn

A column-switching system based on semi-microcolumns was used for direct an alysis of omeprazole and omeprazole sulfone in human plasma samples. Plasma samples were injected into a mixed-function (MF Ph-1) column (35 mmx4.6 mm I.D.) to remove proteins and other non-specific peak producing substances from the analyte-containing time zone. The analyte-containing fraction was thereafter transferred to a C-18 semi-microcolumn (250 mmx1.5 mm I.D.) afte r concentration at the C-18 intermediate column. The absorbance at 302 nm i n a ultraviolet (UV) detector was recorded to measure the concentration. Th e detection limit for omeprazole and omeprazole sulfone in the present meth od was 10 ng/ml. Interbatch variation (coefficient of variation) of the QC samples spanned less than 10% and intra-batch variation less than 2%. The r ecovery ratios of omeprazole and omeprazole sulfone were over 98%. The curr ent method can be used as a simpler procedure with similar sensitivity and reproducibility as previously reported methods. (C) 2001 Elsevier Science B .V. All rights reserved.