Fast, affordable and eco-friendly enzyme kinetic method for the assay of α-ketoglutaric acid in medical product and sports supplements.

A novel kinetic method was developed for the quantitation of α-ketoglutaric acid (AKG) in cardioplegic solution and athletic supplements. The assay relied on an enzymatic transamination of AKG and d-4-hydroxyphenylglycine to form 4-hydroxybenzoylformic acid and l-glutamic acid using d-phenylglycine aminotransferase. Since 4-hydroxybenzoylformic acid absorbed UV strongly at 334 nm, the initial rate of the reaction was determined by the increasing absorbance at this wavelength without the need for colorimetric probes or coupling reactions, and this information was used for the construction of a standard curve against AKG concentration. The method showed good linearity (r2 = 0.9994) over an AKG concentration range of 20-160 µM. The limits of detection and quantitation were 4.09 and 13.62 µM respectively. It was simple, inexpensive, accurate and precise, as well as repeatable, and was not interfered with by excipients in the samples. Regarding the environmental friendliness, the method was free from the use of organic solvents or hazardous reagents and required no chemical pre-treatment of samples. The proposed method gave assay results tested in real samples in agreement with the HPLC method and commercial assay kits, therefore being suitable for routine analysis of AKG in quality control laboratories.