Comparative evaluation of colorimetry, GLC and HPLC for the determination of urinary hippuric acid.

Abstract

Human urine samples, 81 from the non-exposed, 36 from those with intensive exposures to tolueue, and 23 from the less intensively exposed, were analyzed for hippuric acid by colorimetry, gas liquid chromatography (GLC), and high perform-ance liquid chromatography (HPLC). The colorimetric method always gave higher values than the GLC method. In the case of the non-exposed, the value by the former method was more than double the value by the latter. When the colori-metric values were plotted on the abscissa against the GLC values on the ordinate, the slope of the calculated regression line was 0.444 for the non-exposed while it was 0.882 for the exposed. The value was higher as the exposure was more intensive.A conversion formula between colorimetric and GLC values was calculated from the values observed and it was y=x(1-1.78e-0.43x)+0.50 where x and y are the colorimetric and GLC values (mg/ml), respectively, with a correlation coefficient of 0.82. The equation is however not applicable when x is smaller than 0.6. The HPLC values essentially agreed with the GLC values, the regression line being y=0.993z+ 0.009 where y and z are the GLC and HPLC values (mg/ml), respectively. The correla-tion coefficient, r, was 0.994.