Analysis of Phenothiazine and Its Derivatives Using LC/Electrochemistry/MS and LC/Electrochemistry/Fluorescence

The on-line electrochemical conversion of phenothiazine and its derivatives after liquid chromatographic separation has been studied by mass spectrometry and fluorescence spectroscopy. In an electrochemical cell consisting of porous glassy carbon, the phenothiazines are readily converted to oxidized products, which can be detected by on-line fluorescence spectroscopy and mass spectrometry. The method allows rapid investigations on the electrochemical oxidation pathways, as demonstrated for phenothiazine itself. The phenothiazine derivatives are transferred into their strongly fluorescent sulfoxides. Based on this reaction, an LC/electrochemistry/fluorescence method was developed that allows for limits of detection between 5 × 10^-9 and 4 × 10^-8 mol/L and limits of quantification between 2 × 10^-8 and 1 × 10^-7 mol/L for the individual phenothiazines. The linear ranges comprised three decades starting at the limit of quantification.