Colorimetric method for determination of urinary methylmalonic acid.

The colorimetric method for the determination of methylmalonic acid by coupling with diazotised p-nitroaniline has been re-examined. Extraction of the diazotised product into amyl alcohol and tetra-methyl ammonium hydroxide considerably increases its stability and sensitivity and reduces background absorbance. Preliminary solvent extraction and ion-exchange chromatography are desirable but can be accomplished simply and quickly using very small quantities of urine. In this form, the method is very reliable and gives recoveries of about 95% and a coefficient of variation of about 7%.