Published:Journal of Chromatographic Science,
ISSN 0021-9665Volume
38, Number 4, April 2000, pp. 162–168
Simple
In-Line Postcolumn Oxidation and Derivatization for the Simultaneous Analysis
of Ascorbic and Dehydroascorbic Acids in FoodsA.
Bognár Federal Research Center for Nutrition—Institute of Chemistry
and Biology, Garbenstr. 13, Stuttgart 70599, Germany H.G. Daood Central Food Research Institute, Herman Ottó u. 15,
Budapest 1022, Hungary
A new analytical
procedure for the simultaneous determination of L-ascorbic acid (AA), isoascorbic
acid (IAA), L-dehydroascorbic acid (DHAA), and isodehydroascorbic acid (IDHAA)
in food by high-performance liquid chromatography (HPLC) is developed. After
separation on an HPLC column, an in-line oxidation of AA and IAA to DHAA and
IDHAA, respectively, is performed on a short column of activated charcoal. The
dehydroascorbic acids are derivatized with a 1,2-phenylenediamine solution in
a heated capillary Tefzel reactor into fluorescent quinoxaline compounds and
monitored fluorometrically. The chromatographic method provides good separation
of LAA, LDHAA, and their diastereoisomers in a relatively short time (~10 min).
After optimization of postcolumn derivatization conditions, calibration runs
and recovery tests are performed. The fluorescent response in terms of peak
area is highly proportional to the concentration of all derivatives examined
over a range of 0.1 to 100 µg/mL solution for LAA, LDHAA, IAA, and IDHAA.
Recoveries were in the range of 97 to 103%. The detection limit is 0.1 mg of
each ascorbic acid derivative per 100 g food. A wide variety of foods (fruits,
fruit juices, vegetables, vegetable products, milk, liver, and sausage) are
analyzed by the developed procedure. The Vitamin C (LAA and LDHA) contents determined
according to the present analytical method are in the same order of magnitude
as the result of precolumn derivatization and the fluorometric methods. The
described method is a highly specific procedure for determining Vitamin C in
food. It is simple to handle, only slightly susceptible to disturbance, perfectly
suitable for serial determinations, and yields reproducible results.
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