Abstract
A new accurate direct colorimetric method by p-dimethyl-aminobenzaldehyde (DAB) for determining the concentration of urinary hippuric acid and methylhipp-uric acids as indices of toluene or xylenes exposure was devised by us.
To 0.02 ml of urine containing hippuric acid, 2.0 ml of 0.4% DAB solution in pyridine and 1.0 ml of acetic anhydride were added, and the solution was kept at 30°C for 1 hr. after thoroughly mixing. Then, the absorbance was determined at 460 nm. against a blank solution containing acetic anhydride, DAB and pyridine and water instead of urine.
This direct and sensitive colorimetric method for the determination of hippuric acid in urine is applicable to the concentrations under at least 2.0 mg/ml of water or urine according to Beer-Lowbert law.
The variation coefficient in the determination of hippuric acid by this method was small ranging from 1.3 to 2.7%, and the recovery was between 100.5 and 104.8% when a urine sample contained about 1.0-2.0 mg hippuric acid per ml of the urine. In the present paper, moreover, normal value of urinary hippuric acid determined by this method is described.
As on application of this new method, urinary hippuric acid and methylhippuric acids in the urine of six workers in shipbuilding yard, who used paint thinner containing both toluene and m-xylene, were determined.
