DETERMINATION OF 6,7-DIFLUORO-1-(2,4-DIFLUOROPHENYL)-1,4-DIHYDRO-4-OXO-3-QUINILINECARBOXYLIC ACID AND RELATED-COMPOUNDS BY HIGH-PERFORMANCE LIQUID-CHROMATOGRAPHY

6,7-Difluoro- 1-(2,4-difluorophenyl)- 1,4-dihydro-4-oxo-3-quinilinecarboxylic acid (Abbott-72931) and related compounds are determined by high performance liquid chromatography (HPLC). A two-pan assay procedure quantitates both the drug substance and the related compounds. The chromatography used is based on a Bakerbond(R) C-4 column with a 0.04 M citrate buffer (pH 4.4) eluent modified with THF. Detection is at 254 nm. Quantitation of Abbott-72931 is achieved using an external standard method and an Abbott-72931 reference standard. An isocratic HPLC system is used with a 75% buffer/25% THF eluent. Assay precision (RSD values) for two lots of Abbott-72931 ranged from +/- 0.66% to +/- 0.97%. Quantitation of related compounds in Abbott-72931 is achieved by an external standard method using the same chromatography, with gradient elution to remove the more strongly retained impurities from the column. Unhydrolyzed Abbott-72931 ethyl ester is quantitated using an Abbott-72931 ethyl ester reference standard. Other compounds are quantitated versus the Abbott-72931 reference standard. Assay precision of related compounds determined in two lots of Abbott-72931 at levels of 0.04% to 1.0% ranged from +/- 58% to +/- 6.8%. Detector response for Abbott-72931 and Abbott-72931 ethyl ester is linear to at least 25.4 and 9.9-mu-m-g/mL, respectively (correlation coefficients > 0.999, essentially intersecting the origin). Recovery of known related compounds of Abbott-72931 ranged from 94.4 to 107.5% when added to the drug substance at levels of 0.2% to 2.0%.