Study of the solid-phase extraction of diclofenac sodium, indomethacin and phenylbutazone for their analysis in human urine by liquid chromatography.

A selective semi-automated solid-phase extraction (SPE) of the non-steroidal anti-inflammatory drugs diclofenac sodium, indomethacin and phenylbutazone from urine prior to high-performance liquid chromatography was investigated. The drugs were recovered from urine buffered at pH 5.0 using C18 Bond-Elut cartridges as solid sorbent material and mixtures of methanol-aqueous buffer or acetonitrile-aqueous buffer as washing and elution solvents. The extracts were chromatographed on a reversed-phase ODS column using 10 mM acetate buffer (pH 4.0)-acetonitrile (58:42, v/v) as the mobile phase, and the effluent from the column was monitored at 210 nm with ultraviolet detection. Absolute recoveries of the anti-inflammatory drugs within the range 0.02-1.0 microg/ml were about 85% for diclofenac and indomethacin, and 50% for phenylbutazone without any interference from endogenous compounds of the urine. The within-day and between-day repeatabilities were in all cases less than 5% and 10%, respectively. Limits of detection were 0.007 microg/ml for diclofenac sodium and indomethacin and 0.035 microg/ml for phenylbutazone, whereas limits of quantitation were 0.02 microg/ml for diclofenac and indomethacin and 0.1 microg/ml for phenylbutazone.