Simultaneous gas chromatographic determination of urinary mandelic and phenylglyoxylic acids using diazomethane derivatization

Summary A new gas chromatographic method is proposed for the simultaneous determination of mandelic and phenylglyoxylic acids in human urine. The two acids are extracted into ethyl acetate from acidified and ammonium sulphate-saturated urine, converted into methyl esters with diazomethane and chromatographed in this form.Gaseous diazomethane is generated in a simple apparatus and introduced by a mild nitrogen flow into the extract of the investigated urine. Completion of esterification is indicated by an external indicator (chloroform solution of iodine). When the pink colouring of the indicator disappears, further supply of diazomethane is stopped. Since only the exact amount of diazomethane needed enters the reaction, any adverse effects of its excess cannot assert themselves. Phenylglyoxylic acid is transformed quantitatively into the corresponding methyl ester without formation of any secondary products. The method permits simple, rapid and reliable determination of the two above named acids in human urine. It is used with success in biological monitoring of industrial styrene exposure.