Storage of urine samples and correction for metabolite concentration in urine for biological monitoring of organic solvents

An attempt was made to establish a method for the direct determination of urinary concentration of creatinine, hippuric acid (HA), methylhippuric acids (MHA) and mandelic acid (MA) by high performance liquid chromatography (HPLC). For assays of stored urine samples, urine was spotted on filter paper or filter paper was dipped in urine. The filter paper was dried and kept several weeks, and then MA, HA, o-MHA, (m+P)-MHA and creatinine in the filter paper were eluted with 50 vol% methanol, and their concentration were determined by the HPLC method. The correlation coefficient found between the concentration of organic solvents (toluene and xylene) in the air and of the metabolites (HA and MHA) in worker's urine, corrected for creatinine and /or specific gravity, was higher than that between the organic solvent concentrations and the uncorrected metabolite concentrations. The ratio of HA concentration to creatinine concentration in the urine of students unexposed to toluene after physical exercise was similar to that before exercise. Individual spot samples of urine of unexposed subjects were measured for HA over 24-hours at appropriate intervals. When HA in these specimens was calculated with correction for creatinine and/or specific gravity, the variation coefficient was reduced. In cases of spot samples of workers' urine, correction for creatinine and/or specific gravity is practically useful in both individual and group urine analysis. Especially in over concen-trated urine samples, satisfactory results can be obtained by correcting fer creatinine rather than correcting for specific gravity.