Abstract
A new simple and reliable spectrophotometric method is described to determine glyoxylic acid in its synthesis reaction mixture containing oxalic acid, glycolic acid, acetic acid, glyoxal, and ethylene glycol by means of a modified Hopkins–Cole reaction between glyoxylic acid and tryptophan in presence of ferric chloride and concentrated sulphuric acid. The linear range of glyoxylic acid concentration is 0–0.028 M. The limits of detection (LOD) and quantitation (LOQ) are 0.0019 M and 0.00577 M, respectively. The LOD, LOQ, standard deviation, relative standard deviation, and recovery ratio of the proposed method are comparable with a selected HPLC reference method. Both methods displayed same precision and credibility. Reaction stoichiometry between tryptophan and glyoxylic acid is assumed to be 2 : 3. Reaction mechanism has been postulated based on identified molar ratios of reactants. Glyoxal gave a negative test with tryptophan although it is a dialdehyde.
Highlights
Glyoxylic acid (GA) is an important organic acid in the chemical, cosmetic, pharmaceutical, and food industries
Is paper provides a simple, reliable, and inexpensive spectrophotometric method for determination of glyoxylic acid in such reaction mixtures directly without the need of separation. e method depends on a colored chromogen product formation between glyoxylic acid and tryptophan when they react according to a reaction discovered in 1901 by Hopkins and Cole [4] (see equation (1)). ey suggested that one molecule of glyoxylic acid can react with two molecules of tryptophan to give a crimson-violet color that absorbs at 540–545 nm. is reaction ideally occurs in an anhydrous medium pledged by concentrated sulphuric acid [5,6,7,8]: International Journal of Analytical Chemistry
The Hopkins–Cole reaction test by means of the proposed method is selective only to glyoxylic acid without any interference of other compounds of the studied mixture including the glyoxal containing aldehyde group. e baseline, has to be zero set using the blank sample in order to compensate the minor effect of ferric chloride interaction with tryptophan
Summary
Glyoxylic acid (GA) is an important organic acid in the chemical, cosmetic, pharmaceutical, and food industries. It is found in plants and involved in the metabolic cycle of animals. E determination of glyoxylic acid in its electrochemical synthesis reaction mixture is a difficult process because this mixture contains carboxylic acids with convergent acidic dissociation constants and other compounds carrying organic groups that can undergo oxidation or reduction such as ethylene glycol, glyoxal, and glycolic acid. Us, it is expected that glyoxylic acid will be very difficult to determine quantitatively using traditional analytical methods such as acid-base or redox titrations, separation, or precipitation [2, 3].
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