Preliminary study on near-infrared spectroscopic measurement of urine hippuric acid for the screening of biological exposure index

摘要

Biological Exposure Indices (BEIs) are reference for a chemical or its metabolite in the biological specimen. BEIs give guidelines for the evaluation of potential health hazards or for diagnosis of occupational illnesses. Among them, urine hippuric acid (HA) that is a metabolites of toluene is considered as the BEIs of toluene exposure for human and measured from workers using toluene. In this study, we attempted to develop a brief measurement of urine HA by using near-infrared spectroscopy. As the first step, water solutions of hippuric acid of several concentrations (0-250mg/dl) are measured. Afterward, artificial urines conditioned by adding glucose and urine to HA solutions were measured and analyzed. The solvents are optically measured within near infrared region (750-2500nm) obtaining optical absorption. Then, differential absorbance were calculated by subtraction of analyte absorbance from ion-exchange water absorbance and analyzed. As a result, for HA solutions, a calibration equation from absorbance in two wavelengths can be obtained by using multiple regression (R2=0.935). However, this calibration cannot provide a good estimation for artificial urines. Secondary, another calibration from three wavelengths was obtained and providing a good regression (R2=0.934). This result suggests that a brief urine constituents measurement using near-infrared spectroscopy can be developed.