Determination of folic acid by ion-pair RP-HPLC in vitamin-fortified fruit juices after solid-phase extraction

A sensitive and reliable method was developed for the determination of folic acid (FA) in vitamin-fortified fruit juices and fruit drinks. After solid-phase extraction clean-up with strong-anion-exchange material, FA was determined by ion-pair reversed phase high-performance liquid chromatography (RP-HPLC). Limits of detection (LOD) and quantitation (LOQ) were 0.04 and 0.06 mg/l, respectively. Average recoveries at two fortified levels (0.5 and 1.0 mg/l) were 97% in 0.1 M acetate buffer (pH 4.9) and ranged from 78 to 93% in spiked blackcurrant nectar, apple juice, and cherry nectar, with standard deviations less than 2.3%. The method was used to analyze nine commercial fruit juices and fruit drinks containing FA in the range of 0.30–1.40 mg/l. In two samples significantly less FA was found than specified.