A gas-chromatographic method for urinary organic acid analysis is described, designed to be used routinely for the diagnosis of organic aciduria. It involves extraction of urine with ethyl acetate, dehydration of extract residues, and trimethylsilylation. Organic acids are identified by using an extensive list of retention indices published in the accompanying paper (this issue). Quantitative values are given for organic acids in urines from 50 ostensibly normal subjects. Typical chromatograms of urinary organic acids from patients with eight well-established organic acidurias are also shown.

Gas-chromatographic retention indices are given, in terms of methylene units, for 155 metabolically important compounds (mostly organic acids) as trimethylsilyl derivatives on 10% OV-1 and 10% OV-17 columns. Comprehensive references on metabolic diseases that can be diagnosed by detection of these metabolites are cross-indexed to facilitate the use of the methylene-unit list. With the data presented here, it is now possible to diagnose more than 25 well-defined organic acidurias by use of gas chromatography alone.