Estimation of micro-extraction process hippuric acid for toluene exposure monitoring in urine samples

This study employed a quick, efficient, sensitive, and easy-to-use micro-extraction process to monitor biomarker hippuric acid (BIHA) in urine samples as a bioindicator of exposure to toluene with an HPLC-DAD instrument. The independent variables for the micro-extraction process of hippuric acid were examined, while the response from the HA monitoring acted as the dependent variable. Initial screening and parameter optimization were performed using the multivariate models. The desirability function aimed to maximize the extraction recovery of hippuric acid while minimizing solvent volume and extraction time. The best conditions identified were: 152 µL of extractant solvent, extraction time 253 s (4.2 min), a salt amount of 3.9%W/V, and pH = 2.7 with Desirability = 1. Achieving Desirability = 1 reflects a perfect compromise of all goals. The suggested model showed strong validation, evidenced by adjusted R² = 0.9888, high recovery rates, low error in confirmation runs (1.37-2.09%), and consistent predicted values. The model demonstrated satisfactory recovery rates, emphasizing its potential for analyzing urine samples as an indicator of toluene exposure. The detection limit was established at 0.15 ng mL^-1 for hippuric acid, with a calibration curve linear of 1 to 900 ng mL^-1. Assessments of samples conducted with this model established its validity and resulted in adequate efficiency. The precision assessment of the technique (as %RSD) was found to be in the range of 2.11-4.25%.