Development of a quantitative method for the analysis of total L-ascorbic acid in foods by high-performance liquid chromatography.
A new method has been developed for the determination of total vitamin C in foods. The method requires less time than the traditional methodologies and uses a radical oxidation of L-ascorbic acid (AA) to obtain dehydro-L-ascorbic acid (DHAA) by means of a peroxyl radical generated in situ by thermal decomposition of an azo-compound, 2,2'-azobis(2-amidinopropane) dihydrochloride (AAPH). The dehydro-L-ascorbic acid is condensed with benzene-1,2-diamine (o-phenylenediamine, OPDA) to form its highly fluorescent quinoxaline derivative, 3-(1,2-dihydroxyethyl)furo[3,4-b]quinoxaline-1-one (DFQ), which is then separated on a C(18) column eluted with a mobile phase of 80 mM phosphate buffer and methanol at pH=7.8 and detected fluorometrically at lambda(ex)=355 nm and lambda(em)=425 nm. The reaction conditions for the complete conversion of AA to DFQ were 56 degrees C, 36 min and a mumol AAPH/AA ratio of 60. The sample, extracted with an aqueous metaphosphoric acid solution, was analyzed after being filtered through a 0.45 microm membrane. The method has shown good repeatability, sensitivity and accuracy compared to the results obtained with the reference method. The response of the detection system was linear within a range of 0.5-8.0 microg/mL with a correlation coefficient of 0.9997. The limit of detection was 0.27 microg/mL and the limit of quantification was 0.83 microg/mL. The AA contents of some selected foods were analyzed.
Burini
Giovanni
G
Department of Internal Medicine, Section of Applied Biochemistry and Nutritional Sciences, University of Perugia, Via San Costanzo, 06126 - Perugia, Italy. gburini@unipg.it
D000578:Amidines / Q000737:chemistry; D001205:Ascorbic Acid / Q000032:analysis*; D002851:Chromatography, High Pressure Liquid / Q000379:methods*; D003683:Dehydroascorbic Acid / Q000032:analysis / Q000138:chemical synthesis; D005470:Fluorometry; D005504:Food Analysis / Q000379:methods*; D010084:Oxidation-Reduction
D000578:Amidines; C046728:2,2'-azobis(2-amidinopropane); D001205:Ascorbic Acid; D003683:Dehydroascorbic Acid