Analysis of chlormequat in human urine as a biomarker of exposure using liquid chromatography triple quadrupole mass spectrometry

Abstract

In this study, a method using liquid chromatography triple quadrupole mass spectrometry (LC/MS/MS) is described for the analysis of the plant growth regulator chlormequat (CCC) in human urine. Analysis was carried out using selected reaction monitoring (SRM) in the positive ion mode. [(2)H(4)] labeled CCC as internal standard (IS) was used for quantification of CCC. The limit of detection (LOD) was determined to 0.1 ng/mL. The method was linear in the range 0.3-800 ng/mL urine and had a within-run precision of 4-9%. The between-run precision was determined at urine levels of 7.0 and 31 ng/mL and found to be 5 and 6% respectively. The reproducibility was 3-6%. To validate CCC as a biomarker of exposure, the method was applied in a human experimental oral exposure to CCC. Two healthy volunteers received 25 μg/kg b.w. CCC in a single oral dose followed by urine sampling for 46 h post-exposure. The CCC was estimated to follow a first order kinetic and a two compartment model with an elimination half-life of 2-3h and 10-14 h respectively. One hundred 24h urine samples were collected from non-occupationally exposed individuals in the general population in southern Sweden. All samples had detectable levels above the LOD 0.1 ng/mL urine. The median levels were 4 ng/mL of CCC in unadjusted urine. The levels found in the population samples are several magnitudes lower than those found in the experimental exposure, which corresponds to an oral exposure of 50% of the ADI for CCC.