The use of reversed phase cartridges (C18) in processing plasma for analysis of indomethacin by high performance...

The purpose of these studies was to develop a high performance liquid chromatographic (HPLC) assay for plasma levels of indomethacin. A reversed phase (C18 Sep-Pak) cartridge was used to process plasma for absorption of indomethacin, the internal standard, and impurities. The recovery of plasma indomethacin and the added internal standard was quantitative from 0.5 ml of plasma. The assay was linear from 50 micrograms/l to 10 mg/l without concentration of the effluent from the Sep-Pak cartridge. The intra-assay coefficients of variation, for ten injections each to calibrate points at 0.15, 0.30, 0.50 and 1.00 mg/l, were 8.15%, 6.29%, 5.47% and 5.39%, respectively and for duplicates of duplicate calibration points were 7.51%, 6.32%, 4.41%, and 2.05%, respectively. The inter-assay coefficients of variation were 8.49%, 6.48%, 5.10%, and 2.22%, respectively. The sensitivity of the assay can be increased by a 3-5 fold concentration of the effluent from the Sep-Pak and preliminary experiments have indicated that as little as 100 microliter of starting plasma can be utilized in the assay. The assay can be used to determine the concentration of indomethacin in small volumes of plasma. Since C18 Sep-Pak cartridges were employed to remove contaminating substances, sensitivity and reproducibility were both high while column longevity and efficiency were excellent.