Gas chromatography of urinary aromatic acids

Abstract

A method is described for the separation and identification of 29 aromatic acids by gas chromatography. Aromatic acids without phenolic groups are converted to their methyl esters by reaction with ethereal diazomethane and chromatographed on an 8% ethylene glycol adipate column at 170°C. Phenolic acids are converted to their methyl ester derivatives by ethereal diazomethane and chromatographed on a 3% neopentyl glycol adipate column at 187°C. When other compounds in the urinary extracts overlap with these peaks, a second derivative, the methyl esterified O-methyl ether is prepared by reaction with diazomethane and methanol overnight, and chromatographed on the same column. Indolic acids are converted to their methyl esters with diazomethane and chromatographed on a 2% silicone (SE-30) column at 180°C. When the indolic hydroxyl groups are present, as in 5-hydroxyindoleacetic acid, the methyl esterified O-methyl ether derivative may be prepared if necessary and chromatographed at the same temperature. In certain cases such as vanilmandelic acid, the preferred derivative has an inconveniently long retention time at 187°C on the polar column and an inconveniently short retention time at 180°C on the nonpolar column. This derivative may best be determined at a higher temperature (210–225°) on the polar column.