Use of ¹⁹F-nuclear magnetic resonance and gas chromatography-electron capture detection in the quantitative analysis of fluorine-containing metabolites in urine of sevoflurane-anaesthetized patients

Abstract

1. The use of fluorine-19 nuclear magnetic resonance (¹⁹F-NMR) and gas chromatography-electron capture detection (GC-ECD) in the analysis of fluorine-containing products in the urine of sevoflurane-exposed patients was explored.

2. Ten patients were anaesthetized by sevoflurane for 135–660 min at a flow rate of 6 l min⁻¹. Urine samples were collected before, directly after and 24 h after discontinuation of anaesthesia.

3. ¹⁹F-NMR analysis of the urines showed the presence of several fluorine-containing metabolites. The main oxidative metabolite, hexafluoroisopropanol (HFIP)-glucuronide, showed two strong quartet signals in the ¹⁹F-NMR spectrum. HFIP concentrations after β-glucuronidase treatment were quantified by ¹⁹F-nuclear magnetic resonance. Concentrations directly after and 24 h after discontinuation of anaesthesia were 131 ± 41 (mean ± SEM) and 61 ± 19 mol mg⁻¹ creatinine, respectively. Urinary HFIP excretions correlated with sevoflurane exposure.

4. Longer scanning times enabled the measurement of signals from two compound A-derived metabolites, i.e. compound A mercapturic acid I (CAMA-I) and compound A mercapturic acid II (CAMA-II), as well as products from β-lyase activation of the respective cysteine conjugates of compound A. The signals of the mercapturic acids, 3,3,3-trifluoro-2-(fluoromethoxy)-propanoic acid and 3,3,3-trifluorolactic acid were visible after combining and concentrating the patient urines. CAMA-I and -II excretions in patients were completed after 24 h.

5. Since ¹⁹F-nuclear magnetic resonance is not sensitive enough, urinary mercapturic acids concentrations were quantified by gas chromatography-electron capture detection. CAMA-I and -II urinary concentrations were 2.3 ± 0.7 and 1.4 ± 0.4 mol mg⁻¹ creatinine, respectively. Urinary excretion of CAMA-I showed a correlation with sevoflurane exposure, whereas CAMA-II did not.

6. The results show that ¹⁹F-nuclear magnetic resonance is a very selective and convenient technique to detect and quantify HFIP in non-concentrated human urine. ¹⁹F-nuclear magnetic resonance can also be used to monitor the oxidative biotransformation of sevoflurane in anaesthetized patients. Compound A-derived mercapturic acids and 3,3,3-trifluoro-2-(fluoromethoxy)-propanoic acid and 3,3,3-trifluorolactic acid, however, require more sensitive techniques such as gas chromatography-electron capture detection and/or gas chromatography-mass spectrometry for quantification.