Determination of Isocitric Acid in Citrus Juice—A Comparison of HPLC, Enzyme Set and Capillary Isotachophoresis Methods

Three different analytical procedures for the determination of dl -isocitric acid content in citrus fruit juices were compared. The dl -isocitric acid is an important marker in multicomponent procedures for the evaluation of authenticity and quality of fruit products. The compared procedures were the new proposed capillary isotachophoresis (CITP) procedure using coupled two capillaries, reverse-phase high-pressure liquid chromatography (HPLC) method and enzymic procedure (Boehringer Mannheim). The optimized CITP electrolyte system was: 6m m HCl+3.8m m BisTrisPropan+2m m CaCl2+0.05% hydroxypropylmethyl cellulose (leading electrolyte) and 5mm morpholinethanesulphonic acid+1sssssm m BisTrisPropan (terminating electrolyte). The best correlation was found between the CITP and enzymic procedure (r=0.956, n=6), the other cross-correlation coefficients were 0.850 and 0.748 for HPLC–enzymic and HPLC–CITP, respectively.