Ultra-high-performance liquid chromatography–tandem mass spectrometry measurement of climbazole deposition from hair care products onto artificial skin and human scalp

A validated LC-MS/MS method for the quantification of climbazole metabolites in human urine

Climbazole is a preservative and an anti-dandruff ingredient with applications in various cosmetic products. The general population is therefore exposed to this chemical, and exposure monitoring is desirable. We have postulated a pathway for the human metabolism of climbazole, leading to two specific metabolites which can be excreted via urine. An analytical method for the determination of these metabolites in human urine was developed and validated. The sample preparation includes an enzymatic hydrolysis protocol. The measurement as such is based on online solid phase extraction (SPE), coupled to ultra-high-performance liquid chromatography-tandem mass spectrometry (UHPLC-MS/MS). Intra- and inter-series coefficients of variation (CV) were determined in the concentration range from 1 µg/l to 100 µg/l with spiked pooled urine samples, and they were consistently below 15%, mostly below 10%. The corresponding accuracies (mean relative recovery rates) in spiked pooled urine varied from 97% to 103%. The robustness of the method was estimated by spiking individual urine samples. At 1 µg/l, the robustness was rather limited due to interfering matrix peaks in several samples, but excellent results were obtained at 10 µg/l and 100 µg/l, with CVs between 7% and 14% and accuracies from 101% to 110%. Matrix interferences often seemed to be associated with higher creatinine contents (≥2.0 g/l) of the samples. We subsequently applied the method to urine specimens from a human metabolism study involving documented climbazole exposures. We were able to identify and quantify the postulated metabolites in those real samples, thus validating our metabolism hypothesis. We also investigated the precision and accuracy of the enzymatic deconjugation with the real samples. The deconjugation step was found to be highly repeatable and largely quantitative. Both metabolites formed glucuronides, though varying fractions were also excreted in unconjugated (free) forms. Phase II conjugates other than glucuronides did not seem to be produced in significant amounts. With our method, both climbazole metabolites can be reliably quantified in the range between about 1.5 µg/l (depending on matrix interferences in individual samples) and at least 500 µg/l.

Dummy molecularly imprinted solid phase extraction of climbazole from environmental water samples

Dummy molecularly imprinted polymer (DMIP) for climbazole (CBZ) was synthesized for the first time employing miconazole (MNZ) as the dummy template together with methacrylic acid (MAA) monomer, ethylene glycol dimethacrylate (EGDMA) cross-linker and acetonitrile (ACN) porogen. The selectivity and capacity of the prepared MNZ-DMIP was estimated for CBZ by high-performance liquid chromatography (HPLC) and equilibrium binding experiments. Imprinting factor (IF) with a value of 7.0 was achieved, much higher than the CBZ templated MIP (IF = 3.5). Heterogeneous binding sites were found in the MNZ-DMIP, the corresponding saturation capacity and dissociation constant for the high and low affinity binding sites were 6.761 μmol g^-1 and 0.3027 mmol L^-1, 43.60 μmol g^-1 and 4.055 mmol L^-1, respectively. High efficient method based on dummy molecularly imprinted solid phase extraction (DMISPE) coupled with HPLC was established for the selective enrichment of CBZ in river and tap water using MNZ-DMIP as sorbent. DMISPE conditions including sample loading pH/volume, selective washing and elution solvents were carefully optimized. The developed method showed good recoveries (82.3-96.2%) and repeatability (RSDs 0.6-4.9%, n = 5) for samples spiked at three different concentration levels (0.2, 1.0 and 5.0 μg L^-1). The detection limit was determined as 0.012 μg L^-1. The results demonstrated good potential of this method for sample pretreatment of CBZ in environmental water samples.