A supercritical fluid chromatographic method using packed columns for phenylbutazone and oxyphenbutazone in serum, and for phenylbutazone in a dosage form.

The separation of phenylbutazone (PB) and its major metabolite oxyphenbutazone (OPB) using supercritical fluid chromatography (SFC) has been investigated. The separations were studied on octadecylsilane, silica and cyano packed columns with 5% methanol in carbon dioxide as mobile phase and detection at 240 nm. The octadecylsilane column showed the most favourable chromatographic parameters for the analysis of the analytes. Recoveries of PB and OPB from spiked human serum were in the 82-83% range using solid phase extraction on an ODS cartridge. Limits of detection of the SFC assay were 0.1 microgram ml-1 for PB and 1.0 microgram ml-1 for OPB. Accuracy and precision of the method were in the 0.24-4.94% range for PB and OPB. The SFC method was directly comparable to an HPLC assay of the same analytes. The SFC method was also applied to a commercial 100 mg dosage form of PB with good recovery of PB.