Simple and sensitive GC/MS-method for the quantification of urinary phenol, o- and m-cresol and ethylphenols as biomarkers of exposure to industrial solvents

•A method for simultaneous quantification of urinary phenol and 4 biomarkers of exposure to solvents was established and validated.•High sensitivity (LOD 10 and 20 μg/L for cresol and ethylphenol) and excellent precision and accuracy for the analytes even at low levels.•The method was successfully applied in proficiency testings.•We quantified background levels of o-, m-cresol and 4-ethylphenol in urine of the general population.•The excretion of urinary 4-ethylphenol is highly correlated to smoking habits.

We have developed and validated a simple and sensitive method for the determination of urinary phenol as well as the urinary metabolites of toluene and ethylbenzene in one analytical run. After enzymatic hydrolysis for the cleavage of conjugates overnight, the analytes are extracted from the matrix with a liquid–liquid extraction procedure using toluene as solvent under acidic conditions. The analytes are then derivatised to volatile ethers using N,O-bis(trimethylsilyl) trifluoroacetamid (BSTFA) for cresols and ethylphenols as well as N-tert-butyldimethylsilyl-N-methyltrifluoroacetamid (MTBSTFA) for the determination of phenol. Separation and detection was carried out using capillary gas chromatography with mass-selective detection (GC–MS). Deuterium-labeled o-cresol served as internal standard for the quantification of all metabolites and guaranteed good accuracy of the results. No matrix effects were observed in the quantification of the analytes. The limit of detection for o- and m-cresol and 2- and 4-ethylphenol was 10 and 20 μg/l urine and linearity ranged up to 3 and 12 mg/L urine, respectively. The limit of detection for urinary phenol was 0.5 mg/L with a linear range up to 200 mg/L. The relative standard deviation of the within-series imprecision ranged between 3.0 and 7.2% at two spiked concentrations of 60 and 400 μg/l and the relative recovery was between 84 and 104%, depending on the analyte. The method was successfully applied in proficiency testing for urinary o-cresol and phenol.This method was used for the analysis of urine samples of 17 non-smoking and 13 smoking persons from the general population without known exposure to solvents. Smokers showed a significantly higher excretion of o-cresol (median: 23 vs. 33 μg/l), m-cresol (median: 43 vs. 129 μg/l) as well as 4-ethylphenol (median: 25 vs. 124 μg/l). Especially excretion of 4-ethylphenol was significantly correlated to smoking habits. The method seems to be suitable for biological monitoring of low-level solvent exposures and allows determination of background values in the general population.