Electrochemically assisted Fenton reaction: reaction of hydroxyl radicals with xenobiotics followed by on-line analysis with high-performance liquid chromatography/tandem mass spectrometry.
Oxygen radicals are generated in vivo by various processes, often as toxic intermediates in different metabolic transformations, and have been shown to play an important role for a large number of diseases. In this article we introduce an electrochemical flow-through system that allows generation of hydroxyl radicals for reaction with xenobiotics and subsequent detection of the oxidation products on-line with high-performance liquid chromatography/tandem mass spectrometry (HPLC/MS/MS). The system is based on the Fenton reaction and is predominantly aimed at the generation of hydroxyl radicals; however, by minor variations to the system, a broad range of other radicals can be produced. Optimization of the system was performed with the radical scavenger 5,5-dimethyl-1-pyrroline-N-oxide (DMPO). Under the same physical conditions, one injection through the electrochemical cell gave a higher yield of the oxidation product N-hydroxy-5,5-dimethylpyrrolidin-2-one than what was attained after 60 min with a chemical Fenton system catalyzed by ascorbic acid. Since the iron is added as Fe(3+), the initial mixture is 'inactive' until it reaches the electrochemical cell. This makes it very suitable for on-line analysis of the generated compounds, since the whole reaction mixture, including substrate, can be kept in a vial in an autosampler. The system described provides a useful tool for investigation of new radical scavengers and antioxidants. Since the hydroxyl radical adds readily to unsaturated pi-systems, the technique is also suitable for on-line generation and characterization of potential drug metabolites resulting from hydroxylation of double bonds and aromatic systems.
D002851:Chromatography, High Pressure Liquid; D004492:Edetic Acid / Q000737:chemistry; D004563:Electrochemistry; D004578:Electron Spin Resonance Spectroscopy; D005609:Free Radicals / Q000737:chemistry; D017665:Hydroxyl Radical / Q000737:chemistry*; D007202:Indicators and Reagents; D007501:Iron / Q000737:chemistry; D013058:Mass Spectrometry; D009862:Online Systems; D013056:Spectrophotometry, Ultraviolet; D015262:Xenobiotics / Q000737:chemistry*
D005609:Free Radicals; D007202:Indicators and Reagents; D015262:Xenobiotics; D017665:Hydroxyl Radical; D004492:Edetic Acid; D007501:Iron