EFFECT OF WATER-CONTENT ON SENSITIVITY AND STABILITY OF THE M-PHENYLPHENOL URONIC-ACID ASSAY

The influence of climate and hence analytical environment on the uroni c acid assay of Blumenkrantz and Asboe-Hansen (Anal. Biochem., 54 (197 3) 484-9) is described. Instability of diagnostic chromophore is attri buted to variations in the water content of the sulfuric acid-tetrabor ate reagent used. Water, when added to the sulfuric acid-tetraborate r eagent to a final concentration of 1-10% (v/v), caused a significant r eduction in color intensity developed by the m-phenylphenol reagent. T he acid-tetraborate reagent absorbed water from the atmosphere under h igh relative humidity (RH), owing to its high (85% v/v) sulfuric acid contents. Absorption of water by the reagent increased as RH and tempe rature increased, and color intensity correspondingly decreased. Expos ure of the acid-tetraborate reagent to 25 degrees C and 99% RH for 24 h caused a 30% decrease in chromophore intensity. This phenomenon was prevented by decreasing the aqueous sample size in the assay from 200 to 100 mu l. To maximize stability of the reaction, the reagent should be stored under N-2 in a tightly sealed bottle. Also, in particularly hot and humid geographic locations, the aqueous sample size should be reduced by one-half.