Hydrophobic chromatography and bioanalysis of some polar pyridine derivatives used as antilipolytic agents

The antilipolytic compound 5-fluoro-3-pyridinecarboxylic acid and 5-fluoro-3-hydroxymethylpyridine have been determined quantitatively in plasma (Srel = 5-7% in the concentration range 1-20 microgram/ml) by liquid chromatography on LiChrosorb RP-8 (5 micrometer) with phosphate buffer pH 3-4 as mobile phase, after precipitation of proteins and direct injection of the supernatant. Detection limits were 0.1-0.2 microgram/ml. The chromatographic retention is explained by adsorption of the uncharged compounds on to the support complemented by ion-pair adsorption with buffer components at extreme pH values.