Ics i000

The specific conditions of TCE analysis can be found in our previous research [23 (link)]. The recovery of TCE was in the range of 87–95%. Chloride anion was analyzed by ion chromatography (Dionex ICS-I000, Sunnyvale, CA), and the measured Cl⁻ concentration before SPC addition in HA-Fe(II)-EDDS-catalyzed SPC system served as a background level. Total soluble iron including total free iron (Fe²⁺ and Fe³⁺) and EDDS chelated iron (Fe(II)-EDDS and Fe(III)-EDDS) in Fe(II)-EDDS-catalyzed SPC and HA-Fe(II)-EDDS-catalyzed SPC systems was determined with inductively coupled plasma-optical emission spectrometery (ICP-OES, Agilent 725ES, Santa Clara, USA). Free ferrous ions (Fe²⁺) as well as total free iron (Fe²⁺ and Fe³⁺) were measured with the 1,10-phenanthroline method [24 (link)]. The solution pH was recorded by a pH meter (Mettler-Toledo DELTA 320).

One microliter (1-μL) extracted TCE or CT samples were analyzed immediately by a gas chromatograph (Agilent 7890A, Palo Alto, CA) equipped with an electron capture detector (ECD), an autosampler (Agilent 7693), and a DB-VRX column (60 m length, 250 μm i.d., and 1.4 μm thickness). The split ratio was 20:1. The injector and detector temperatures were 240 and 260°C, respectively, and the temperature of oven was held at 75°C constantly. TCE recovery was in the range of 87-95%. Analysis procedure of extracted CT samples is in accordance with TCE analysis procedure except the constant oven temperature of 100°C. Extracted NB samples were analyzed using flame ionization detector (FID) equipped with a HP-5 column (30 m length, 250 μm i.d., and 0.25 μm thickness), keeping temperatures of injector, detector and oven at 250°C, 300°C, and 175°C, respectively. 1-μL extracted NB samples were injected into GC at a split ratio of 5:1. Ion chromatography (Dionex ICS-I000, Sunnyvale, CA) was applied to detect the concentration of chloride anion (Cl^-) and formic acid (HCOOH). The measured concentration of chloride anion with HAH addition before adding SPC in HAH/CA/Fe(II)/SPC system was acted as a background level. Fe(II) and total soluble iron were determined with 1,10-phenanthroline method [28 (link)]. pH values were measured by a pH meter (Mettler-Toledo DELTA 320, Greifensee, Switzerland).

Aqueous samples (1.0 mL) containing TCE, CT, or NB were extracted with n-hexane (1.0 mL) for gas chromatograph (GC) analysis. The average extraction recovery rates of TCE, CT, and NB are 89.7%, 87.5%, and 93.1%, and the relative standard deviations are 3.1%, 1.9% and 1.2%, respectively. The organic phase was injected to a gas chromatograph for quantification (Agilent 7890A, Palo Alto, CA, USA). DB-VRX column (60 m length, 250 μm i.d., and 1.4 μm thickness) and electron capture detector (ECD) was used for detection of TCE and CT while the temperatures of the injector, detector and oven were set at 240, 260 and 75°C respectively. HP-5 column (30 m length, 250 μm i.d., and 0.25 μm thickness) and flame ionization detector (FID) were used to quantify NB while the injector, detector and oven temperatures were 250, 300 and 175°C, respectively. The detection limit of the above method for TCE is 1 μg·L⁻¹, and the linear range is 0.1–25 mg·L⁻¹, with a correlation coefficient (R²) of 0.9992. Chloride anions released from TCE were analyzed by ion chromatography (Dionex ICS-I000, Sunnyvale, CA, USA). Soluble ferric ion (Fe(III)) in aqueous solution was reduced to ferrous ion (Fe(II)) by hydroxylamine chloride and then determined with the 1,10-phenanthroline method [21 (link)]. H₂O₂ concentration in aqueous solution was quantified spectrophotometrically with the titanium sulfate method [22 ].