Validation of a Column-Switching High-Performance Liquid Chromatographic (HPLC) Method for Determination of ML-1035 and Its Five Metabolites in Plasma

A fully automated column-switching HPLC procedure has been developed and validated for quantitation of ML-1035 and its five metabolites in plasma employing direct injection. Plasma samples were injected onto a CN extraction column (4 × 4.6 mm, 5 µm) for micellar cleanup with 0.5% sodium dodecyl sulfate (SDS) in 50 mM phosphate. The proteinaceous components were solubilized and flushed out. The extracted compounds were then eluted by forward flush onto a C8 analytical column (150 × 4.6 mm, 5 µm) for further analysis using fluorescence detection (excitation, 308 nM; emission, 350 nm). After the subsequent washing and reequilibration with a sequence of three solvent mixtures, the extraction column was ready for the next injection. The limit of quantitation for all compounds of interest was about 10 to 15 ng/ml using 100 µl of plasma. Excellent precision, accuracy, and linearity were obtained for all compounds over a range of 10 to 1500 ng/ml. The practicality of the HPLC method was also validated with plasma samples from dogs receiving ML-1035. Longevity for both extraction and analytical columns is excellent. Micellar cleanup coupled with the column-switching technique is a promising HPLC procedure when using direct injection of biological fluids.