Urinary organic acids: isolation and quantification for routine metabolic screening.

A method for isolating organic acids from acidified urine on an equivolume mixture of Porapak Q and Porapak T is described, and results are compared with extraction with ethyl acetate and ion exchange on DEAE-Sephadex. Average recoveries of 14C-labeled oxalic acid, lactic acid, succinic acid, alpha-ketoglutaric acid, citric acid, and cinnamic acid were equal to or better than those obtained with the solvent-extraction method. The ion-exchange method gave higher recoveries for oxalic acid, lactic acid, and citric acid. The quantification of separated acids from reconstructed mass spectrometric ion traces is compared with quantification from the simultaneously recorded flame ionization detector response signals. A good correlation was obtained. With the present routine metabolic screening method we have detected several patients with inborn errors of metabolism.