Toc analyzer

The residual concentration of OG and RhB in the reaction system were detected using UV spectrophotometer, at detection wavelengths 475 nm and 554 nm, respectively. The residual concentrations of ACT, STZ and BPA were determined form high performance liquid chromatography (LC-20A, Shimadzu, Japan) with a photodiode array detector (SPDM20A). A Zorbax SB-C18 column (4.6 × 250 mm, 5 μm) (Agilent, USA) was used at a column temperature of 30 °C. A mixture of methanol (A)/0.3% formic acid solution (B) (30 : 70, v/v, for ACT and STZ; 70 : 30, v/v, for BPA) was used as the mobile phase at a flow rate of 1.0 mL min⁻¹. Total organic carbon (TOC) was determined using a TOC analyzer (Elementar, Germany). The degradation products were detected using a 7890B/5977C GC-MS (Agilent, USA). The reactive oxide species (ROS) generated form the system was detected using an EPR spectrometer (Bruker A320, USA).

The concentration of DCF was determined by a high-performance liquid chromatograph (HPLC, Waters 2695) equipped with a C18 column (4.6 × 150 mm, 5 μm). The column temperature was 30 °C with the injection volume of 20 μL. The mobile phase consisted of 0.1% acetic acid aqueous solution and methanol (25 : 75, v/v) at a flow rate of 1 mL min⁻¹ and the detection wavelength was set at 276 nm. DCF degradation products were detected by an ultra-high performance liquid chromatograph-quadrupole time-of-flight tandem mass spectrometer (UPLC-QTOF/MS). The C18 column (2.1 × 100 mm, 1.7 μm) was used as a stationary phase with the column temperature of 30 °C. The mobile phase was a mixture of 0.1% formic acid water solution (A) and acetonitrile (B) at a flow rate of 0.3 mL min⁻¹. The gradient elution procedure was 90% A for 1 min constantly, linearly decreasing to 0% A (100% B) for 12 min, keeping for 3 min and slowly increasing to 90% A for 18 min. The injection volume was 10 μL. The electrospray ionization (ESI) was used in the mass spectrometer to scan in the positive ion mode, and the scan range was m/z 50–500. All the mass spectrum data were analyzed by Masslynx 4.1 software. The mineralization of DCF was assessed through measuring the total organic carbon (TOC) of the reaction solution using a TOC analyzer (Elementar). The solution pH was monitored by a pH meter (PHS-3C, Leici).