Quantitative determination of urinary metabolites of geraniol by ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS)

Abstract

Geraniol is a fragrance which occurs in natural terpene oil or is chemically synthesized on a large scale. It is used in a wide variety of consumer products such as perfumes, deodorants, household products and cosmetics. Hence, not only industry workers in the production of geraniol, but also consumers can come into contact with the substance. Human biomonitoring (HBM), i.e. the analytical determination of substances and their metabolites in human biological material, is a key element in the analysis and assessment of the distribution and intensity of occupational and environmental exposure of humans. Therefore, a procedure for the quantitative determination of the urinary metabolites Hildebrandt acid, geranic acid, 3-hydroxycitronellic acid and 8-carboxygeraniol as potential biomarkers of geraniol exposure was developed and validated. The method is based on ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) after enzymatic hydrolysis and liquid–liquid extraction (LLE) of the target analytes. The limit of quantification (LOQ) is 1.5 μg L⁻¹ for 8-carboxygeraniol, 2.7 μg L⁻¹ each for Hildebrandt acid and geranic acid, and 1.8 μg L⁻¹ for 3-hydroxycitronellic acid. The method was applied to urine samples of 41 persons without occupational exposure to geraniol. Hildebrandt acid and geranic acid were detected in all samples, 8-carboxygeraniol in 83% and 3-hydroxycitronellic acid in 81% of the samples. Hildebrandt acid (median: 313 μg L⁻¹, range: 37–1966 μg L⁻¹) was the most abundant metabolite, followed by geranic acid (93 μg L⁻¹; 9–477 μg L⁻¹), 3-hydroxycitronellic acid (18 μg L⁻¹; <LOQ to 70 μg L⁻¹) and 8-carboxygeraniol (9 μg L⁻¹; <LOQ to 46 μg L⁻¹). Hildebrandt acid, geranic acid and 3-hydroxycitronellic acid apparently represent larger relative fractions of the eliminated metabolites, but they are not strictly specific for geraniol since they are metabolites of other terpenes as well, such as citral. In contrast, geraniol seems to be the only parent compound for 8-carboxygeraniol, which makes this metabolite a promising candidate for specific human biomonitoring and risk assessment.