Rapid microbore liquid chromatographic analysis of biphenyldimethyl dicarboxylate in human plasma with on-line column switching

A fully automated method including microbore liquid chromatography and column switching was developed for the analysis of biphenyldimethyl dicarboxylate (DDB) from human plasma samples. After direct injection of plasma samples (100 μl) into the system, deproteinization and analyte fractionation occurred on a Capcell Pak MF Ph-1 column (20x4 mm I.D.) and the DDB fraction was transferred from the MF Ph-1 column to an intermediate column (35x2 mm I.D.) using 15% acetonitrile in phosphate buffer (50 mM, pH 7.0). The main separation was performed on a microbore C₁₈ column (150x1.5 mm I.D.) using 45% acetonitrile in water. The method showed excellent sensitivity (detection limit of 5 ng/ml) and good precision (C.V.≤3.0%), and shortened total analysis time (20 min). In the concentration range of 5-200 ng/ml, the mean recovery was 90.7±1.8% and the response was linear (r²≥0.999).