New fully automated gas chromatographic analysis of urinary S‐phenylmercapturic acid in isotopic dilution using negative chemical ionization with isobutane as reagent gas

• Published in: Journal of mass spectrometry. 2020-07, Vol.55 (7), p.n/a
• Main Authors: Dugheri, Stefano, Mucci, Nicola, Cappelli, Giovanni, Bonari, Alessandro, Campagna, Marcello, Arcangeli, Giulio, Bartolucci, Gianluca
• Format: Article
• Language: English
• Subjects: Analysis; Argon; Automation; Benzene; Biomarkers; Biomonitoring; Chromatography; Creatinine; Design of experiments; Dilution; Environmental monitoring; Experimental design; Exposure limits; Gas chromatography; Gas mixtures; Gases; Hydrocarbons; Ion sources; Ionization; Ions; isotopic dilution; Mass spectrometry; Mass spectroscopy; Methane; negative chemical ionization; Occupational exposure; Occupational health; Optimization; Phenylmercapturic acid; Reagents; Scientific imaging; Spectroscopy; SPME; S‐phenylmercapturic acid
• ISSN: 1076-5174; 1096-9888
• DOI: 10.1002/jms.4481

The determination of urinary S‐phenylmercapturic acid (S‐PMA) represents the most reliable biomarker to monitor the intake risk of airborne benzene. Recently, the European Chemical Agency deliberated new occupational exposure limits for benzene and recommended an S‐PMA biological limit value of 2‐μg/g creatinine. This limit is an order of magnitude lower than the previous one, and its determination constitutes a challenge in the analytical field. We developed and validated a method that allows the fully automated and sensitive determination of S‐PMA by the use of gas‐chromatography negative chemical ionization tandem mass spectrometry in isotopic dilution. For negative chemical ionization, we selected a mixture of 1% isobutane in argon as reactive gas, by studying its chemical ionization mechanism and optimal parameters compared with pure isobutane or pure methane. This gas mixture produces a more abundant signal of the target analyte than isobutane or methane, and it extended the operative lifetime of the ion source, enabling us to start a high‐throughput approach of the S‐PMA analysis. Moreover, energy‐resolved mass spectrometry experiments were carried out to refine the MS/MS analysis conditions, testing nitrogen and argon as collision gases. The method optimization was pursued by a chemometric model by using the experimental design. The quantification limit for S‐PMA was 0.10 μg/L. Accuracy (between 98.3% and 99.6%) and precision (ranging from 1.6% to 6.4%) were also evaluated. In conclusion, the newly developed assay represents a powerful tool for the robust, reliable, and sensitive quantification of urinary S‐PMA, and because of its automation, it is well suited for application in large environmental and biological monitoring.