Miniaturized TOC analyzer using dielectric barrier discharge for catalytic oxidation vapor generation and point discharge optical emission spectrometry

Highlights: • A DBD-COVG reactor was constructed to convert organic compounds into CO₂ for TOC analysis. • High oxidation efficiency and sensitivity were obtained when coupled with PD-OES for carbon quantification. • The mechanism of the oxidation vapor generation was proposed with electron paramagnetic resonance characterization. • The accuracy was validated by successfully analyzing TOC in real water samples from oil fields. Total organic carbon (TOC) is an important parameter describing organic pollution degree of waters. Due to the increasing need of field analysis and drawbacks of conventional TOC analytical instruments, miniaturized TOC analyzers are still demanding. In this work, a dielectric barrier discharge (DBD) microplasma was utilized for catalytic oxidation vapor generation (COVG) of organic compounds into CO₂, and a point discharge (PD) microplasma was employed to excite the carbon atomic emission spectra for quantification. Sample solution with phosphoric acid and persulfate solution was injected into the DBD-COVG reactor by a syringe to convert organic compounds into CO₂ efficiently and quickly, which was subsequently transported into the point discharge optical emission spectrometer (PD-OES) for detecting carbon at 193.09 nm. Under optimal experimental conditions, high oxidation efficiencies for several organic compounds were achieved, i.e., 96.4%, 95.1% and 94.3% for 50 mg L⁻¹ potassium hydrogen phthalate (KHP), sodium laurylsulfonate and phenol, respectively. A limit of detection (LOD) of 0.02 mg L⁻¹ (as C) was obtained, with a precision of 3.9% (relative standard deviation, RSD) at 15 mg L⁻¹ TOC standard (as C). The possible catalytic oxidation mechanism was proposed with the characteristic results of electron paramagnetic resonance (EPR). Its potential environmental application was demonstrated by successfully analyzing TOC in underground water, surface river water and surface sedimentary water samples from oil fields, with analytical results agreed well with those obtained by the commercial high-temperature combustion coupled nondispersive infrared absorption (HTC-NDIR) technique.