Development and validation of an LC method for the quantitation of carbenicillin in human serum

An LC method for the quantitation of carbenicillin in human serum has been developed and validated. After protein precipitation with acetonitrile and evaporation, the residue was taken up by citric acid at pH 1.9. Carbenicillin and the internal standard (I.S.), piperacillin, were extracted with ethyl acetate, evaporated to dryness and reconstituted with a buffer solution. The separation of carbenicillin,, the I.S., and matrix peaks was achieved on a Microsorb C18, 3 microns column with a mobile phase of acetonitrile-tetrabutylammonium-phosphate buffer (pH* 6.6). The detection was by UV at 208 nm. The run time was 8 min. The established linearity range was 0.25-20 microgram ml-1 (r2 > 0.99) with a limit of quantitation of 0.25 microgram ml-1. Interday precision (RSD) and bias over the entire range were 1.1-6.9% and -1.83 to +2.80%, respectively. The interday precision (RSD) and bias for the QC samples at 0.75, 3.0 and 12 micrograms ml-1 were 5.9-7.9% and -2.80 to +2.30%, respectively. Stabilities of on-system, bench top, freeze-thaw cycles and sample storage were established.