A comparison of two methods for quantifying D-glucaric acid

The relative usefulness of two spectrophotometric methods for quantifying urinary D-glucaric acid was evaluated. The enzyme inhibition method measures the inhibition of beta-D-glucuronidase by the 1,4-glucarolactone produced from D-glucaric acid in urine by boiling at acidic pH. The glyoxylic acid method measures glyoxylic acid produced from the oxidation of D-glucaric acid which has first been separated from other urinary compounds by ion exchange chromatography. For a group of 61 healthy adults, the enzyme inhibition method gave a range similar to that of previously reported values: 0 to 6.44 mmol D-glucaric acid/mol creatinine (99% confidence limits). Similar values were obtained from standard solutions by the two methods. Recovery was approximately 105% by both methods. Urinary concentrations, however, were often from 3 to 10 times higher by the glyoxylic acid method. The higher values were probably due to interference from ascorbic acid and other glyoxylic acid-producing compounds, because the reduction of interfering compounds with sodium borohydride before chromatography resulted in concentrations of less than half of those originally observed. It is concluded that the modification of the enzyme inhibition method is preferable because it is less subject to interference and less labor intensive than the glyoxylic acid method.