Direct injection HPLC analysis of some non-steroidal anti-inflammatory drugs on restricted access media columns

Direct serum injection methods are described for the HPLC determination of selected non-steroidal anti-inflammatory drugs (NSAIDS) on restricted access media (RAM) columns, using either a Pinkerton (ISRP) or semi-permeable surface (SPS) column. Twenty microlitres of a filtered serum sample was injected directly onto each column. Calibration curves were prepared for ketoprofen (1-20 micrograms/mL), fenbufen (0.8-20 micrograms/mL), sulindac (0.8-20 micrograms/mL) and probenecid (1.5-40 micrograms/mL) on the SPS column, and nabumetone (1.5-40 micrograms/mL) and indomethacin (1.5-40 micrograms/mL) on the Pinkerton column. The percentage error and imprecision of the methods were found to be less than 10%. The inter- and intra-day variability for analytes were in the range of 0.15-10%. The limits of quantitation and detection were in the range of 800-1500 and 300-800 ng/mL, respectively, for the analytes studied. A hydrophobic shielded phase (Hisep) column was also investigated and was found to be generally too retentive (> 29 min) for assay of these analytes.