Determinação fotométrica do ácido ascórbico

Leme Junior, Jorge; Malavolta, E.

doi:10.1590/S0071-12761950000100016

Resumo

The photometric determination of ascorbic acid with the "E. E. L. portable colorimeter" can be carried" out rapid and conveniently using either 3% HPO3 or 0,4% (COOH) 2 as protective agent. The standards would contain from 2 to 20 micrograms of ascorbic acid per ml of metaphosphoric or oxalic acid solutions. We mix 10 ml of these solutions with 3 ml of the adequate citrate buffer solutions, and we pipet 5 ml of the resulting mixture to a matched test tube containing 5 ml of sodium - 2,6 - dichlorobenzenoneindophenol (80 mg per liter); then we shake well and after 15 seconds the extintion is read using green filter. The readings are subtracted from the blank one. Designating the differences by x and the concentrations of ascorbic acid/ml in the standards by y, we get, with the acid of the method of least squares, the following regression equations: for the metaphosphoric acid Y = 0,543x + 0,629 for the oxalic acid Y = 0,516x + 0,422, which permit, by interpolating, the determination of the ascorbic acid content in plant materials.

^IDocente Livre e Assistente de Tecnologia Agrícola. Escola Superior de Agricultura "Luiz de Queiroz"

^IIAssistente de Química Agrícola. Escola Superior de Agricultura "Luiz de Queiroz"

SUMMARY

The photometric determination of ascorbic acid with the "E. E. L. portable colorimeter" can be carried" out rapid and conveniently using either 3% HPO3 or 0,4% (COOH) 2 as protective agent. The standards would contain from 2 to 20 micrograms of ascorbic acid per ml of metaphosphoric or oxalic acid solutions. We mix 10 ml of these solutions with 3 ml of the adequate citrate buffer solutions, and we pipet 5 ml of the resulting mixture to a matched test tube containing 5 ml of sodium - 2,6 - dichlorobenzenoneindophenol (80 mg per liter); then we shake well and after 15 seconds the extintion is read using green filter. The readings are subtracted from the blank one. Designating the differences by x and the concentrations of ascorbic acid/ml in the standards by y, we get, with the acid of the method of least squares, the following regression equations:

for the metaphosphoric acid Y = 0,543x + 0,629

for the oxalic acid Y = 0,516x + 0,422,

which permit, by interpolating, the determination of the ascorbic acid content in plant materials.

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LITERATURA CITADA

FISHER, RONALD A. and FRANK YATES 1943 Statistical tables for biological, agricultural and medical research, Second Edition, Oliver and Boyd Ltd., London - Edinburgh.
GOMES FREDERICO PIMENTEL e EURIPEDES MALAVOLTA. 1949 Considerações matemáticas sobre a lei de Mitscherlich. Boletim n.o 3 da Esc. Sup. Agr. "Luiz de Queiroz", Piracicaba.
ORSINI, DEMOSTENES e OTÁVIO DE PAULA SANTOS. 1943 Determinação da vitamina C em alguns frutos brasileiros pelo colorimetro fotoelétrico. Separata da Resenha Clinico-Científica, Ano XII - Dezembro de 1943 - N.o 12.
PONTING, J. D. 1943 Extraction of ascorbic acid from plant materials. Indus. and Engin. Chem., Anal. Edit. 15:381-391.