Sorption-photometric determination of ascorbic acid using molybdosilicic heteropolyacid and polyurethane foam after microwave irradiation

An analytical procedure for the determination of ascorbic acid based on the reduction of molybdosilicic heteropolyacid immobilized on polyurethane foam by ascorbic acid in a microwave oven is developed. A blue-colored product of reduction of molybdosilicic heteropolyacid was determined immediately in the polyurethane foam using diffuse reflectance spectroscopy. The method was used to determine ascorbic acid in the range 0.6-40 mg/ml in the final measured solution. The application of microwave irradiation allows to shorten the analysis time from 20 h to 6.5 min. The substances, which usually accompany ascorbic acid, are tolerable. The proposed method can be applied for the determination of ascorbic acid in fruit juices and pharmaceutical preparations with satisfactory results. The reliability of the method was established by replicate determinations against the official Russian pharmacopoeial method. (C) 1998 Elsevier Science B.V. All rights reserved.