Green detection of trace cyanuric acid and free chlorine together via ion chromatography.

Chlorinated cyanurates (CCAs) are a type of disinfectants currently used worldwide for fight of Coronavirus. However, CCAs upon dosed into water can release not only free chlorine (FC), a strong disinfectant, but also cyanurate (CYA), a persistent compound potentially harmful to human and environment. Therefore, detecting CYA and FC in water are very important not only for ensuring sufficient disinfection but also for monitoring the impacts of FC and CYA on receiving watershed. However, conventional analytical methods for them are mostly based on colorimetric methods, which have high method detection limits (MDLs) and rely on chemical reactions that are likely sensitive to coexisting chemicals. To overcome these issues, we herein proposed a facile and reaction-free method to detect CYA and FC together in just one run by ion chromatography (IC) equipped with both conductivity and ultraviolet absorbance detectors. The method features obvious advantages over colorimetric methods in being lower MDLs (3.6 µg/L for CYA and 9.0 µg/L for FC), environmental-friendly (i.e., no organic solvent involved), and more resistant to alkaline solution. With this method, trace levels of CYA (i.e., 34-44 µg/L), which were nondetectable by conventional method, were found in two river water samples, implying that the local environment was already polluted by CCAs during the pandemic period. Overall, this study demonstrates a robust tool that may assist better understanding and monitoring the fate and transport of trace CCA derivatives in water.

Replacing liquid chromatography with tailored ion chromatography: A green method for detecting furfuryl alcohol and understanding its properties.

Furfuryl alcohol (FFA) is a furan derivative potentially hazardous to human health, and it is now ubiquitously found in foods and used for identifying singlet oxygen (1O2) in environmental studies. However, current analytical methods for FFA in water are mostly based on gas chromatography and liquid chromatography (LC), which inevitably employ organic solvents as extractants or eluents that can result in harmful wastes production and extra treatment costs. To solve this issue, we herein developed a green analytical method to measure FFA without using organic solvents by a tailored ion chromatography (IC) equipped with ultraviolet (UV) detector. The method demonstrated a calibration curve fitting well (R2 > 0.99) for a wide FFA concentration range (i.e., 0.1 ∼ 10.0 mg/L) and a method detection limit (0.031 mg/L) comparable to LC method. The recoveries of FFA dosed into real samples exceeded 86.4% with the relative standard deviations below 2.5%. Next, we examined the property and reactivity of FFA through the method. It was found that FFA's acid-dissociation coefficient (i.e., pKa) was not 9.55, which disagrees with an earlier report. FFA was resistant to 254 nm UV or hydrogen peroxide (H2O2) but vulnerable to H2O2-assisted 254 nm UV or 185 nm vacuum UV, confirming that FFA was sensitive to hydroxyl radicals. Interestingly, FFA was degraded to less extent in water dosed with both sodium hypochlorite (NaOCl) and H2O2 than that dosed with NaOCl only, suggesting that the reaction between NaOCl and H2O2 does not produce 1O2. Given that this IC method can analyze FFA, NaOCl, and H2O2 simultaneously in one run, the evidences presented here may have helped clear a controversy about the 1O2 formation possibility by NaOCl and H2O2.

Total organic fluorine (TOF) analysis by completely converting TOF into fluoride with vacuum ultraviolet.

Quantifying total organic fluorine (TOF) in water is vital in monitoring the occurrence and persistence of all fluorine-containing organic compounds in the environment, while currently most studies focus on analyzing individual fluorine-containing organic compounds. To fill the technology gap, we herein proposed to convert TOF completely into fluoride with vacuum ultraviolet (VUV) photolysis, followed by analysis of fluoride with ion chromatography. Results showed that the tailored VUV photoreactor achieved satisfying recoveries of fluorine from ten model TOF compounds not only in ultrapure water (83.9 ± 2.0% to 109.4 ± 0.8%) but also in real water samples (92.1 ± 1.0%-106.2 ± 15.7%). Unlike other ultraviolet-based processes that favor alkaline conditions, this VUV process preferred either neutral or acidic conditions to defluorinate selected compounds. While the mechanisms remain to be explored in the future, it has been evidenced that the photo-degradation and photo-defluorination rates of these TOF compounds varied significantly among compounds and operation conditions. The method obtained a method detection limit (MDL) of 0.15 µg-F/L, which is lower than the MDLs of many other TOF analytical methods, along with excellent calibration curves for concentrations ranging from 0.01 to 10.0 mg-F/L. Notably, minimizing fluoride in sample prior to photoconversion was necessary to avoid subtraction-induced errors for TOF measurement, especially when the fluoride/TOF ratio was high. The robust VUV is also green for sample pretreatment due to its unreliance of chemicals or additives.