Determination of Volatile Disinfection Byproducts in Water by Gas Chromatography–Triple Quadrupole Mass Spectrometry

Trihalomethanes in water samples: Recent update on pretreatment and detection methods

Trihalomethanes (THMs) are classified as volatile organic compounds, considered to be a disinfection by-product during water disinfection process. THMs have been shown to be cytotoxic, genotoxic and mutagenic, with a risk of cancer when they contact with people directly. To protect public health and monitor water quality, it is important to monitor and measure THMs in drinking water. Therefore, it is crucial to develop fast, accurate, highly sensitivity and green analysis methods of THMs in various complicated matrices. Here, this review presents an overall summary of the current state of the pretreatment and detection methods for THMs in various sample matrices since 2005. In addition to the traditionally used pretreatment methods for THMs (such as headspace extraction, microwave-assisted extraction, liquid-liquid extraction), the new-developed methods, including solid-phase extraction, QuEChERS and different microextraction methods, have been summarized. The detection methods include gas chromatography-based methods, sensors and several other approaches. Additionally, benefits and limitations of different techniques were also discussed and compared. This study is anticipated to offer fruitful insights into the further advancement and widespread applications of pretreatment and detection technologies for THMs as well as for related substances.

The impact of inorganic ions on the solar photolysis of chlorinated dissolved organic matter from different sources: Spectral characteristics, disinfection byproducts, and biotoxicities

Dissolved organic matter (DOM) from wastewater treatment plant (WWTP) effluent is chlorinated and then discharged into natural waters, where it is subject to solar irradiation. However, the impacts of inorganic ions in natural waters on the photochemical transformations of the chlorinated DOM (DOM-Cl) have not been studied comprehensively. In this study, variations in the spectral characteristics, disinfection byproducts (DBPs), and biotoxicities of DOM-Cl under solar irradiation at different pH values and in the presence of NO3- and HCO3- were revealed. Three sources of DOM, including DOM from a WWTP effluent, natural organic matter from the Suwannee River, and DOM from plant leaf leachate, were investigated. Solar irradiation resulted in the oxidation of the highly reactive aromatic structures and then reduced the amounts of chromophoric and fluorescent DOM, especially under alkaline conditions. Moreover, alkaline conditions significantly promoted the detected DBPs degradation and the biotoxicities attenuation, while NO3- and HCO3- generally impeded them (or did not work). Dehalogenation of the unknown halogenated DBPs and photolysis of the nonhalogenated organics were the main mechanisms for the DOM-Cl biotoxicity reductions. Hence, improving the ecological safety of WWTP effluents could be achieved through solar irradiation by removing the DBPs formed.

Performance of microbubble ozonation on treated tropical peat water: Effects on THM4 and HAA5 precursor formation based on DOM hydrophobicity fractions

The hydrophobicity properties of dissolved organic matter (DOM) found in tropical peat water has an impact on the formation of carcinogenic DBPs such as trihalomethanes-4 (THM4) and haloacetic acids-5 (HAA5). This study was conducted to determine the effect of microbubble ozonation on changes in DOM fraction and its effect on the formation of THM4 and HAA5. Alum coagulation and activated carbon adsorption were carried out to reduce the DOM concentration before microbubble ozonation. Microbubble ozonation was carried out at acidic (pH 5.5), neutral (pH 7) and alkaline (pH 8.5) conditions to determine the effect of pH. Coagulation and adsorption of activated carbon were successful in reducing the presence of the hydrophobic acid fraction (HPOA) in peat water completely, but the transphilic (TPH), charged hydrophilic (HPIC) and neutral hydrophilic (HPIN) fractions remained in the water. Microbubble ozonation succeeded in decreasing the presence of TPH fraction but increased the formation of HPIC and HPIN. The degradation of the TPH fraction resulted in reduced formation of chlorinated THM4 and HAA5 (C-THM4 and C-HAA5). On the other hand, the formation of HPIC and HPIN fractions increased the formation of brominated THM4 and HAA5 (B-THM4 and B-HAA5) after the final chlorination process.

[Simultaneous determination of six haloacetonitriles in finished water for drinking by purge and trap-gas chromatography-triple quadrupole mass spectrometry]

Haloacetonitriles (HANs) are widely used in finished water as unregulated disinfection by-products. HANs may pose much threat to human health, and there is no relevant standard examination method for these compounds. A method was established for the simultaneous determination of six HANs (chloroacetonitrile (CAN), dichloroacetonitrile (DCAN), trichloroacetonitrile (TCAN), bromoacetonitrile (BAN), bromochloroacetonitrile (BCAN), and dibromoacetonitrile (DBAN)) in finished water by using purge and trap-gas chromatography-triple quadrupole mass spectrometry (GC-MS/MS). The purge and trap technology helps realize automatic determination of samples after collection, without using any harmful reagent. The cost and analytical efficiency of this method were superior to those of solid phase microextraction (SPME). Considering the instability of HANs, the analysis must be carried out as soon as possible after sampling, in order to avoid significant changes in their concentration during storage. In particular, the use of an appropriate quenching agent was critical to sample collection. In this study, ascorbic acid was chosen as the quenching agent. The stabilities of the spiked samples at the levels of 0.1 (TCAN), 0.2 (CAN), 1.0 (DCAN), 1.0 (BAN), 1.0 (BCAN), 4.0 (DBAN) μg/L were tested. The effect of sample storage time (0, 0.5, 1, 2, 3, 4, and 6 h) on the responses of the target component was evaluated. The stability results showed that within 6 h, the relative standard deviations of the responses for the six HANs ranged from 2.32% to 6.98%. To validate the method, first, different traps, viz. 7# (Tenax), 10# (Teanx/silica gel/cms), 11# (VOCARB), and 12# (BTEXTRAP) were optimized. Second, various chromatographic columns (VF-5, Rxi-624, DB-VRX, and HP-INNOWAX) were compared to investigate their influence on the peak shape. Under the optimal detection conditions, the six HANs in finished water were extracted with the 10# trap. The volume of the water sample was used 25 mL, with purging at 35 ℃ for 11 min, and desorbed at 190 ℃ for 1 min. Chromatographic separation was performed on a Rxi-624Sil MS chromatographic column (60 m×0.25 mm×1.40 μm). Gas chromatographic conditions were obtained under the following conditions: split ratio, 1∶10; linear velocity, 30 cm/s. The triple quadrupole mass spectrometer was operated in the electron impact (EI) mode. The target compounds were detected in the multiple reaction monitoring (MRM) mode. Quantitation was carried out using the external standard method. The results showed that the matrix effects of the six HANs ranged from 0.85 to 1.09. Good linearities were obtained in the range of the standard curves. The correlation coefficients (r) were greater than 0.9991. The limits of detection (LODs, S/N=3) were 0.8-120.0 ng/L. The limits of quantification (LOQs, S/N=10) were 1.5-300.0 ng/L. The average recoveries of the six HANs ranged from 84.2% to 106%, and the RSDs were in the range of 1.81%-10.7%. In August 2020, 38 samples of finished water were tested. All of the six HANs were found in the finished water. The concentrations of the HANs were in the range of 0.0101-1.28 μg/L, and the total detection rate was 92.1%. The detection rates of the individual components followed the order DCAN>BCAN>CAN>TCAN>BAN>DBAN. The developed method is efficient, sensitive, and environmentally friendly. It provides a high-quality technical choice for monitoring and health risk assessment of the emerging disinfection by-products of HANs.

Photooxidation of atrazine and its influence on disinfection byproducts formation during post-chlorination: effect of solution pH and mechanism

Partial photooxidation of micropollutants may lead to various degradation intermediates, obviously affecting disinfection byproducts (DBPs) formation during the post-chlorination process. The photooxidation of atrazine (ATZ) in aqueous solutions with low-pressure mercury UV lamps in UV, UV/H2O2 and UV/TiO2 treatment system and the formation of chlorinated disinfection byproducts (DBPs) during subsequent chlorination processes including dichloroacetic acid (DCAA), trichloroacetic acid (TCAA), 1,1,1-trichloro-2-propanone (TCP), trichloromethane (TCM) and chloropicrin (CHP) were investigated in this study. The effect of solution pH on the oxidation pathway of ATZ in three UV photooxidation treatment process and the impact of photooxidation on the DBPs formations were assessed. Based on UPLC-ESI-MS/MS analyses, identification of main oxidation intermediates was performed and the plausible degradation pathways of ATZ in photooxidation system were proposed, indicating that photooxidation of ATZ in UV/H2O2 and UV/TiO2 process system was significantly pH-dependent processes. Dichloroacetic acid (DCAA), trichloroacetic acid (TCAA), 1,1,1-trichloro-2-propanone (TCP), trichloromethane (TCM) and chloropicrin (CHP) were detected in photooxidized ATZ solutions. Compared to the other three DBPs, TCM and TCP were the main DBPs formed. The DBPs formations were greatly promoted in oxidized ATZ solutions. Solution pH and UV irradiation time exhibited obvious impact on the DBPs formation on the basis of DBP species. The variation tendency of DBPs observed relates to the combustion of ATZ in photooxidation system and the production oxidation intermediates.

Effervescence-assisted spiral hollow-fibre liquid-phase microextraction of trihalomethanes, halonitromethanes, haloacetonitriles, and haloketones in drinking water

A new analytical method was optimized to determine 18 disinfection by-products (DBPs) in drinking water, including four different chemical groups. For this purpose, spiral-shaped hollow-fibre liquid phase microextraction with 1-octanol as the acceptor solvent assisted by effervescence was applied using a homemade supporting device that was specifically designed for this application. The device was printed in a 3D printer and allows for an increased fibre surface even with a low sample volume, which significantly facilitates the extraction. The samples were analysed by gas chromatography coupled to both an electron capture detector and a mass spectrometer for the quantification and unequivocal identification of the analytes, respectively. Effervescence was generated using citric acid and bicarbonate at a molar ratio 1:2, which significantly improves the extraction efficiency and reduces mechanical operations, since stirring and modifiers are not required. The results showed enrichment factors ranging from 13.1 to 140.1. Satisfactory recoveries (80-113 %) were obtained, with relative standard deviations from 3 to 15 % and good linearity. The detection limits (ng L^-1) ranged from 10 to 35 (trihalomethanes), 12 to 220 (halonitromethanes), 17 to 79 (haloacetonitriles) and 10 to 16 (haloketones). The applicability of the method was assessed in 6 local water distribution systems.