HPLC/UV determination of organic acids in fruit juices and nectars

A reversed phase HPLC method for separation and determination of organic acids in fruit juices and nectars is presented. The method is based on the reaction of free organic acids with O-(4 nitrobenzyl)-N,N'-diisopropylisourea (PNBDI) in presence of dioxane. Excess of reagent was removed with a strong cation-exchange resin. The p-nitrobenzyl esters were separated on a C₁₈ reversed phase column using gradient elution with water and acetonitrile and UV detection at 265 nm. Benzylmalonic acid was used as internal standard. The determinations were performed in the linear range of 0.05-2 g/l for lactic, acetic and succinic acids, 0.1-12 g/l for tartaric, malic and citric acids. The detection limits were 0.025 g/l, 0.017 g/l, 0.050 g/l, 0.039 g/l, 0.025 g/l and 0.060 g/l, respectively for lactic, acetic, tartaric, malic, succinic and citric acids. Validation of the method was carried out by the standard additions method, the recoveries ranged from 91.4 to 103.0%. The precision of the method was also evaluated and reported a CV% as less than 3.1%. Organic acid profiles of citrus fruit, pineapple and apple natural juices (home-made), commercial juices and nectars were established.