AN IMPROVED METHOD FOR THE DETERMINATION OF NICOTINIC-ACID IN HUMAN PLASMA BY HIGH-PERFORMANCE LIQUID-CHROMATOGRAPHY

A simple, specific, and sensitive HPLC method was developed for the de termination of nicotinic acid in human plasma. Plasma is deproteinized with acetonitrile and centrifuged. The supernatant solution is evapor ated and reconstituted in mobile phase. Separation is achieved using a n IB-SIL CN column with a mobile phase composed of acetonitrile:methan ol:water:acetic acid (700:150:150:1, v/v/v/v). Detection is by ultravi olet absorbance at 263 nm. The retention times of nicotinic acid and 6 -methyl nicotinic acid (internal standard) are approximately 3.8 and 8 .8 minutes, respectively. The assay is linear in concentration ranges of 100 to 10,000 ng/mL (original method) and 20 to 2,000 ng/mL (high-s ensitivity method). The analysis of pooled quality controls (150, 1,25 0, and 7,530 ng/mL) demonstrates excellent precision with relative sta ndard deviations (RSD) (n= 18) of 3.4%, 2.7%, and 2.8%, respectively. For the high sensitivity method, quality control pools prepared at 60, 150, and 1,250 ng/mL had RSDs (n=18) of 5.8%, 2.9%, and 2.8%, respect ively. The method is accurate with all intraday (n=6) and overall (n=1 8) mean values being less than 9% from theoretical at all control conc entrations.