A method for determining haloacetic acid disinfection by-products in drinking water

Abstract

The application discloses a method for determining haloacetic acid disinfection by-products in drinking water, and steps of the method comprise: acidifying a water sample to be measured to strong acidity; adding a sulfate salt into the acidified water sample to be measured, and then adding an extractant to perform extraction, and collecting an organic phase; performing mixing reaction of the organic phase and alcohol to esterify HAAs in the water sample to be measured; after the esterification reaction is completed, adding an aqueous sulfate salt solution, collecting the organic phase by layering, and performing detection by using GC-ECD. In the method, IAA can obtain identifiable chromatographic peaks and good quantitative response, the detection limit of the method is 0.02 mu g / L; at 1 mu g / L and 10 mu g / L of the adding standard level, the recovery rates are 96.9% and 92.3% respectively, and the relative standard deviations are 6.4% and 2.3% respectively; IAA and TCAA can obtain good separation, and meanwhile, other HAAs still maintain good peak out and separation effect, so that the synchronous quantitative determination of IAA and other nine kinds of HAAs can be realized on the GC-ECD platform.

Description

Technical Field

[0001] This invention relates to the field of water quality monitoring and analysis and detection of disinfection byproducts in drinking water, specifically to a gas chromatography method for the detection of multiple haloacetic acid disinfection byproducts in drinking water samples. Background Technology

[0002] During the disinfection of drinking water, natural organic matter, halides and disinfectants react to produce a variety of disinfection byproducts (DBPs), such as trihalomethanes (THMs), haloacetic acids (HAAs), and haloacetonitriles (HANs).

[0003] Currently, domestic and international drinking water standards primarily control halogenated byproducts (DBPs) by focusing on thallium methyl groups (THMs) and halogenated hydroxyl groups (HAAs). Among these, conventional chlorinated byproducts such as chloroform, dichloroacetic acid, and trichloroacetic acid already have relatively mature limit requirements. In recent years, with the intrusion of saltwater, increased bromide / iodide ion concentrations, and the increasing complexity of source water quality, the potential risks of brominated and iodinated DBPs have gradually attracted attention. my country's national standards and some local standards have included novel or unconventional halogenated DBPs such as iodoacetic acid and dichloroiodomethane in appendices or reference indicators, indicating that the identification and determination of low-concentration, highly toxic halogenated byproducts in drinking water is becoming an important direction for water quality monitoring.

[0004] From a detection technology perspective, halogenated DBPs in drinking water are typically at concentrations of μg / L or ng / L, making direct injection insufficient for instrumental detection. Enrichment and pretreatment using methods such as liquid-liquid extraction, solid-phase extraction, solid-phase microextraction, headspace extraction, or purge-and-trap are usually required. Liquid-liquid extraction (LLE) is the most widely used pretreatment method for DBP detection in drinking water due to its ease of operation, low equipment requirements, and relatively low cost. For HAAs, due to their high polarity and low volatility, extraction with organic solvents under acidic conditions and conversion to corresponding ester derivatives via derivatization reagents are usually necessary before analysis. Existing standard detection methods for HAAs mainly include gas chromatography (GC) and liquid chromatography-mass spectrometry (LC-MS). Gas chromatography is typically used in conjunction with an electron capture detector (ECD) or mass spectrometry (MS).

[0005] LC-MS can be used to determine some HAAs and has a certain structural recognition capability. For example, the paper "Comparison of HPLC-MS-MS and GC methods for the determination of nine haloacetic acids in drinking water" by Feng Guixue et al. (China Water & Wastewater, Vol. 39, No. 22, 2023, pp. 144-149) uses HPLC-MS-MS to determine HAA9 in drinking water. However, LC-MS methods usually have problems such as high instrument cost, high maintenance requirements, or limited enrichment capacity.

[0006] GC-ECD exhibits high sensitivity to compounds containing strongly electronegative elements such as chlorine, bromine, and iodine, and its equipment cost is relatively low, making it widely used in routine water quality monitoring laboratories. The US EPA 552.3 method, employing liquid-liquid microextraction, acidification-methanol derivatization, and GC-ECD, is one of the internationally recognized and mature methods for detecting HAAs in drinking water. my country's GB / T 5750.10-2023 also specifies methods for detecting some HAAs in drinking water, with basic principles similar to the EPA 552.3 method, primarily using acidification, salting-out extraction, esterification derivatization, and chromatographic detection as the main technical routes. Existing standard methods mainly focus on HAAs already incorporated into routine monitoring systems. Methods such as EPA 552.3 cover HAA9, and domestic standards such as GB / T 5750.10-2023 also specify methods for determining some HAAs. However, HAA9 does not include iodoacetic acid (IAA), and my country's drinking water standard limits and routine monitoring practices still mainly focus on conventional HAAs such as dichloroacetic acid and trichloroacetic acid.

[0007] Gas chromatography-mass spectrometry (GC-MS) has also been reported in existing technologies. The patent application published by Soochow University, entitled "A Gas Chromatography-Mass Spectrometry Analysis Method for Haloacetic Acids in Drinking Water" (Application No.: 202210857009.9, Publication No.: CN115236229 A), establishes a method for determining various haloacetic acids in drinking water using GC-MS. The target analytes include monochloroacetic acid, dichloroacetic acid, trichloroacetic acid, monobromoacetic acid, dibromoacetic acid, monochlorobromoacetic acid, and monoiodoacetic acid. The main technical route of this method is liquid-liquid extraction, silanization derivatization, and GC-MS selected ion monitoring. The focus is on using mass spectrometry to improve the identification ability of target analytes, making it suitable for haloacetic acid analysis scenarios requiring mass spectrometry confirmation. The patent application published by Shanghai Jiao Tong University, titled "Detection Method of Haloacetic Acids in Drinking Water" (application number 200710046472.0, publication number CN101131381A), uses GC-MS to detect four haloacetic acid standard curves, and the linear fitting coefficients are all greater than 0.999. The patent application published by the Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, titled "A High-Sensitivity Method for Determining the Content of Haloacetic Acid Pollutants" (application number 202410099220.8, publication number CN118067869 A), uses gas chromatography-triple quadrupole mass spectrometry (GC-MS) for detection and analysis, combined with multiple reaction ion scanning (MRI) mode for data acquisition, simultaneously determining nine haloacetic acids in two major categories (chloroalkyl and non-chloroalkyl). While the GC-MS method has strong target identification capabilities, in conventional water quality monitoring scenarios, it requires high standards for instrument configuration, operation and maintenance, and operational standardization, resulting in relatively high costs for widespread application.

[0008] Tongji University's patent application, "A Method for Improving the Accuracy of Haloacetic Acid Gas Chromatography Detection" (Application No.: 202010200905.9, Publication No.: CN 111272927 A), improves the accuracy of haloacetic acid gas chromatography detection by determining the contribution of interfering DBPs to the haloacetic acid detection results during derivatization and correcting the results using a subtraction method. This method does not change the basic workflow of existing haloacetic acid derivatization-gas chromatography detection and mainly belongs to the category of detection result correction methods. Such interference correction methods primarily address the problem of result correction under specific interference conditions. They typically require prior identification of interfering substances and their contribution relationships, and their core lies in back-end concentration correction, rather than overall optimization of the pretreatment and chromatographic separation conditions for the target HAAs.

[0009] With increasing attention being paid to bromine / iodine background water samples and high-risk halogenated byproducts such as iodoacetic acid, it remains necessary to establish GC-ECD determination methods covering chlorinated, brominated, and iodolated HAAs. Furthermore, using the existing HAA9 determination system, the retention times of IAA and trichloroacetic acid (TCAA) are quite similar, making complete separation difficult and thus hindering accurate IAA detection. Therefore, it is still necessary to further improve HAA determination methods based on common GC-ECD platforms to better suit the quantitative analysis of chlorinated, brominated, and iodolated HAAs in actual water treatment processes. Summary of the Invention

[0010] This invention provides a method for determining haloacetic acid disinfection byproducts in drinking water, particularly a method capable of simultaneously detecting HAAs, including IAAs, to address the problems mentioned in the above-mentioned technical background. The HAAs include monochloroacetic acid (MCAA), monobromoacetic acid (MBAA), dichloroacetic acid (DCAA), iodoacetic acid (IAA), trichloroacetic acid (TCAA), bromochloroacetic acid (BCAA), monobromodichloroacetic acid (BDCAA), dibromoacetic acid (DBAA), monochlorodibromoacetic acid (CDBAA), and tribromoacetic acid (TBAA).

[0011] To achieve the above objectives, the method for determining haloacetic acid disinfection byproducts in drinking water according to the present invention includes the following steps: Water sample acidification step: Acidify the water sample to be tested to a strong acidity, for example, pH value ≤ 1, preferably pH value ≤ 0.5; Salting out and extraction steps: Add sulfate to the acidified water sample to be tested, then add the extractant for extraction, and collect the organic phase; Esterification step: The organic phase is mixed with alcohol to react and esterify the HAAs in the water sample to be tested; Secondary salting-out step: After the esterification reaction is completed, add an aqueous sulfate solution and collect the organic phases in layers; GC-ECD Detection Procedure: The organic phase collected in layers is analyzed by GC-ECD. The GC column temperature program is as follows: 30-45℃, hold for 1-5 min; increase the temperature to 50-70℃ at a rate of 2-3℃ / min; then increase the temperature to 100-130℃ at a rate of 7-12℃ / min; then increase the temperature to 170-230℃ at a rate of 15-28℃ / min and hold for 3-8 min; obtain the chromatogram. Quantitative and / or qualitative analysis of HAAs was performed based on the peak area-concentration standard curve, the concentration of the sample to be tested, retention time, and peak area.

[0012] In a preferred embodiment, the acidification of the water sample is preferably carried out using one or more of concentrated sulfuric acid, concentrated hydrochloric acid, and concentrated nitric acid, more preferably using concentrated sulfuric acid.

[0013] In a preferred embodiment, the sulfate used in the salting-out and extraction steps is preferably one or more of sodium sulfate and potassium sulfate, with sodium sulfate being particularly preferred.

[0014] More preferably, for every 30 ml of water sample to be tested, the weight of sulfate used is 3-10 g, preferably 5-8 g, such as 6 g or 7 g.

[0015] In a preferred embodiment, the extractant in the salting-out and extraction steps is preferably methyl tert-butyl ether.

[0016] More preferably, for every 30 ml of water sample to be tested, the volume of the extraction solvent is 1-5 ml, such as 2 ml, 3 ml, or 4 ml.

[0017] In a preferred embodiment, in the salting-out and extraction steps, after the extractant is added, the mixture is shaken or stirred for 1-10 minutes, more preferably 3-8 minutes, and even more preferably 4-6 minutes.

[0018] In a preferred embodiment, the alcohol in the esterification step may be one or more of methanol, ethanol, propanol, and propylene glycol, more preferably methanol.

[0019] In a preferred embodiment, the esterification step is carried out in the presence of an acid, for example, an acidified alcohol esterifies HAAs, wherein the acidified alcohol is acidified with one or more of sulfuric acid, hydrochloric acid, nitric acid, and phosphoric acid, such as sulfuric acid.

[0020] In a preferred embodiment, during the esterification step, each 2 ml of organic phase collected in the salting-out and extraction steps is esterified with 1-5 ml, preferably 2-3 ml, of an acidified alcohol solution with a volume fraction of 5-20%, preferably 10-15%.

[0021] In a preferred embodiment, the esterification step is carried out at 30-60°C, preferably at 45-50°C.

[0022] In a preferred embodiment, the reaction time in the esterification step can be ≥0.5h, more preferably ≥1h, such as 1-5h, and more preferably 2-4h.

[0023] In a preferred embodiment, before secondary salting out, the reaction system after the reaction in the esterification step is completed is cooled to 0-10°C, more preferably 2-8°C, and even more preferably 4-6°C.

[0024] In a preferred embodiment, in the secondary salting-out step, the sulfate may be one or more of sodium sulfate and potassium sulfate, with sodium sulfate being particularly preferred.

[0025] In a preferred embodiment, during the secondary salting-out step, 5-10 ml, preferably 7-8 ml, of a sulfate aqueous solution with a concentration of 100-200 g / L, preferably 150-160 g / L, is added to every 2 ml of organic phase collected from the salting-out and extraction steps.

[0026] In a preferred embodiment, in the secondary salting-out step, after adding the sulfate aqueous solution, the mixture is shaken or stirred for at least 1 minute, preferably 1-5 minutes, and more preferably 2-3 minutes.

[0027] In a preferred embodiment, a residual acid neutralization step is performed after the secondary salting-out step: an alkaline compound is added to the organic phase collected in the secondary salting-out step to neutralize the residual acid.

[0028] More preferably, the alkaline compound may be one or more of hydroxides, oxides, carbonates, and bicarbonates, such as sodium hydroxide, potassium hydroxide, calcium oxide, sodium carbonate, and sodium bicarbonate, more preferably sodium bicarbonate.

[0029] More preferably, the alkaline compound may be added in the form of an aqueous solution, such as a saturated solution. For example, 0.1-5 ml, preferably 1-2 ml, of a saturated solution may be added.

[0030] More preferably, the saturated solution is added in multiple portions (≥2 times), for example, in 2-5 portions, with shaking and / or stirring after each addition.

[0031] After the residual acid neutralization step, the organic phase is collected for GC-ECD detection.

[0032] In a preferred embodiment, the method for constructing the peak area-concentration standard curve includes the following steps: preparing a mixed HAA standard solution of monochloroacetic acid, monobromoacetic acid, dichloroacetic acid, iodoacetic acid, trichloroacetic acid, bromochloroacetic acid, monobromodichloroacetic acid, dibromoacetic acid, monochlorodibromoacetic acid, and tribromoacetic acid, and diluting them to obtain a series of standard solutions with concentrations of 0.1 μg / L, 0.5 μg / L, 1 μg / L, 5 μg / L, 10 μg / L, and 20 μg / L. Each standard solution is subjected to GC-ECD determination using the same method as the water sample to be tested to obtain chromatograms, and a peak area-concentration standard curve is established.

[0033] In a preferred embodiment, in the GC-ECD detection step, the carrier gas is preferably one or more of nitrogen, argon, helium, and neon, with nitrogen being the most preferred.

[0034] In a preferred embodiment, in the GC-ECD detection step, the gas chromatography preferably uses a DB-1701 capillary column (preferably 30.0 m × 0.25 mm × 0.25 μm).

[0035] In a preferred embodiment, during the GC-ECD detection step, the injection port temperature is 200-230℃, preferably 210℃-220℃.

[0036] In a preferred embodiment, the GC-ECD detection step is preferably performed using splitless injection.

[0037] In a preferred embodiment, the injection volume in the GC-ECD detection step is preferably 1 μL.

[0038] In a preferred embodiment, the column flow rate in the GC-ECD detection step is preferably 1.0 mL / min.

[0039] In a preferred embodiment, the detector temperature is preferably 300°C during the GC-ECD detection step.

[0040] In a preferred embodiment, the tail gas flow rate in the GC-ECD detection step is preferably 30 mL / min.

[0041] In a preferred embodiment, the GC column temperature program is as follows: 35-40℃ held for 2-3 min; heated to 60-65℃ at a rate of 2.5℃ / min; then heated to 115-120℃ at a rate of 8-10℃ / min; then heated to 200-210℃ at a rate of 20-25℃ / min and held for 5 min.

[0042] It should be understood that, unless otherwise specified, the sulfates described in this invention are preferably anhydrous sulfates.

[0043] It should be understood that, unless otherwise specified, the HAAs in the present invention and the specific embodiments described herein refer to ten haloacetic acids: monochloroacetic acid, monobromoacetic acid, dichloroacetic acid, iodoacetic acid, trichloroacetic acid, bromochloroacetic acid, monobromodichloroacetic acid, dibromoacetic acid, monochlorodibromoacetic acid, and tribromoacetic acid.

[0044] Compared with the prior art, the technical solution of the present invention has the following beneficial effects: 1) This invention uses 10 HAAs as detection targets, covering monochloroacetic acid, monobromoacetic acid, dichloroacetic acid, iodoacetic acid, trichloroacetic acid, bromochloroacetic acid, monobromodichloroacetic acid, dibromoacetic acid, monochlorodibromoacetic acid, and tribromoacetic acid, taking into account chlorinated, bromo, and mixed chlorobromosubstituted HAAs, and also including iodoacetic acid.

[0045] 2) This invention is based on the GC-ECD platform for detection and does not require GC-MS mass spectrometry confirmation, silanization derivatization, nitrogen blowing concentration or selected ion monitoring as necessary steps. It is applicable to water plant process water quality evaluation and routine water quality monitoring scenarios.

[0046] 3) The present invention preferably defines the conditions for water sample acidification, salting out and liquid-liquid extraction, including the combination of parameters such as the water sample to be tested, acid solution, sulfate and extractant dosage, to promote the transfer of HAAs from the aqueous phase to the organic phase.

[0047] 4) The present invention preferably defines the esterification conditions, that is, the amount and concentration of the alcohol solution, as well as the reaction conditions, are limited according to the volume of the organic phase extract liquid, so that the target HAAs are converted into the corresponding methyl haloacetate.

[0048] 5) This invention employs a two-stage salting-out phase separation, and more preferably, residual acid neutralization treatment. After esterification, sulfate is added for a second-stage salting-out phase separation, and then an alkaline compound is added to the organic phase to neutralize the residual acid solution, thereby reducing the impact of acidified methanol and residual acid on subsequent GC-ECD detection.

[0049] 6) This invention defines GC-ECD conditions applicable to the separation and detection of 10 HAA methyl ester derivatives, including injection port temperature, detector temperature, column flow rate of 1.0 mL / min, and staged temperature program, etc. This invention optimizes the temperature program conditions of the chromatographic column, and IAA and TCAA can be separated well, while other HAAs still maintain good peak elution and separation effect. It can realize the simultaneous quantitative determination of IAA and other 9 HAAs on the GC-ECD platform.

[0050] 7) Using the method of the present invention, IAA can obtain identifiable chromatographic peaks and good quantitative response, with a method detection limit of 0.02 μg / L; at spiked levels of 1 μg / L and 10 μg / L, the recoveries are 96.9% and 92.3%, respectively, and the relative standard deviations are 6.4% and 2.3%, respectively. Attached Figure Description

[0051] Figure 1 This is a chromatogram of a mixed standard of 10 HAAs obtained by the method of this invention. Detailed Implementation

[0052] This invention provides a method for determining haloacetic acid disinfection byproducts in drinking water. To make the objectives, technical solutions, and effects of this invention clearer and more explicit, the invention is further described in detail below with reference to the accompanying drawings and examples. It should be understood that the specific embodiments described herein are only for explaining the invention and are not intended to limit the invention.

[0053] It should be noted that the terms "first," "second," etc., in the specification, claims, and accompanying drawings of this invention are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be used interchangeably where appropriate. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover non-exclusive inclusion. For example, a process, method, system, product, or apparatus that comprises a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to these processes, methods, products, or apparatuses.

[0054] Example 1: In this embodiment, the specific steps are as follows: (1) Acidification of water sample: Add 1.5 mL of concentrated sulfuric acid to 30 mL of water sample to make the water sample under strongly acidic conditions, such as pH value ≤ 0.5. Under this condition, HAAs in the water sample are converted from ionic state to molecular state which is more easily extracted by organic solvents, which is beneficial to subsequent liquid-liquid extraction.

[0055] (2) Salting out and liquid-liquid extraction: Add 6g of anhydrous sodium sulfate to the acidified water sample and shake until fully dissolved to increase the ionic strength of the aqueous phase and promote the transfer of HAAs to the organic phase. Then add 3 mL of methyl tert-butyl ether, shake and extract for 4 min, and obtain the upper organic phase extract after standing and separating the layers.

[0056] (3) Acidified methanol esterification: Take 2 mL of the upper organic phase extract and place it in a derivatization flask. Add 2 mL of 10% (v / v) sulfuric acid-acidified methanol solution, mix well, and react in a 50°C water bath for 2 h to convert monochloroacetic acid, monobromoacetic acid, dichloroacetic acid, iodoacetic acid, trichloroacetic acid, bromochloroacetic acid, monobromodichloroacetic acid, dibromoacetic acid, monochlorodibromoacetic acid, and tribromoacetic acid into the corresponding methyl haloacetic acids. This step is used to improve the volatility and gas chromatography applicability of HAAs, enabling them to be detected by GC-ECD.

[0057] (4) Secondary salting-out phase separation: After the esterification reaction is completed, the sample is cooled at 4°C for 5 min, and then 7 mL of sodium sulfate aqueous solution with a concentration of 150 g / L is added. After shaking for 3 min, the sample is allowed to stand for phase separation. This step is used to promote the separation of the organic phase, acidified methanol phase and aqueous phase, so that the derivatized methyl haloacetate is retained in the organic phase and the influence of acidified methanol and aqueous phase residues on subsequent chromatographic detection is reduced.

[0058] (5) Neutralization of residual acid: After discarding the lower aqueous phase, add a total of 1 mL of saturated sodium bicarbonate solution in four portions to the remaining organic phase to neutralize the residual acid. Shake after each addition of sodium bicarbonate solution to release the carbon dioxide produced in the reaction. After neutralization, allow the phases to separate, and transfer the upper organic phase as the GC-ECD sample.

[0059] (6) GC-ECD separation and detection: A DB-1701 capillary column (30.0 m × 0.25 mm × 0.25 μm) was used, with high-purity nitrogen as the carrier gas. The injection port temperature was 210℃, splitless injection was used, the injection volume was 1 μL, and the column flow rate was 1.0 mL / min. The detector temperature was 300℃, and the tail gas flow rate was 30 mL / min. The column temperature program was as follows: initial temperature 40℃ held for 2 min; temperature increased to 60℃ at 2.5℃ / min; then increased to 115℃ at 10℃ / min; then increased to 200℃ at 20℃ / min and held for 5 min. Under the above chromatographic conditions, methyl ester derivatives of 10 HAAs were separated and detected, and chromatograms were obtained (e.g., chromatograms of HAAs). Figure 1 (As shown).

[0060] (7) Quantitative analysis of standard curve: Prepare a 2 mg / L HAA mixed standard solution and dilute it to obtain a series of standard solutions of 0.1 μg / L, 0.5 μg / L, 1 μg / L, 5 μg / L, 10 μg / L and 20 μg / L. Each standard solution is subjected to GC-ECD determination using the above steps (1)-(6) to establish a peak area-concentration standard curve (refer to Table 1).

[0061] (8) Chromatographic peak identification: such as Figure 1 As shown, after processing with the method of this invention, the 10 HAA mixed standards all produced identifiable chromatographic responses under GC-ECD conditions. The peaks in the figure correspond sequentially to monochloroacetic acid, monobromoacetic acid, dichloroacetic acid, iodoacetic acid, trichloroacetic acid, bromochloroacetic acid, monobromodichloroacetic acid, dibromoacetic acid, monochlorodibromoacetic acid, and tribromoacetic acid, demonstrating the effectiveness of the method of this invention in separating and detecting the 10 HAAs.

[0062] Referring to the peak area-concentration standard curve, the sample to be tested can be qualitatively and / or quantitatively analyzed based on the retention time and peak area.

[0063] To verify the effectiveness of the method of the present invention in the quantitative determination of 10 HAAs in drinking water, the methodology was evaluated from the aspects of standard curve and linear range, method detection limit, precision and accuracy.

[0064] (1) Standard curve and linear range Table 1 Standard Curve and Linear Range As shown in Table 1, the standard curves of the 10 HAAs exhibit good linearity, with correlation coefficients R0. 2 It ranges from 0.9920 to 0.9997.

[0065] (2) Method detection limit, precision and accuracy To evaluate the limit of detection, precision, and accuracy of the method of this invention, method validation was performed using low-concentration spiked samples and spiked recoveries at different concentration levels, with each spike level measured in parallel seven times. The limit of detection (MDL) was calculated based on the standard deviation (SD) of the results from the low-concentration spiked samples, using the formula MDL = 3.14 × SD; precision was expressed as relative standard deviation; and accuracy was expressed as spike recovery. The results are shown in Table 2.

[0066] Table 2. Limit of Detection, Precision, and Spiked Recovery of the Method As shown in Table 2, the method detection limits for the 10 HAAs are 0.01–0.03 μg / L, indicating that the method of the present invention has good detection capability for low concentrations of HAAs in drinking water samples.

[0067] At two spiking levels of 1 μg / L and 10 μg / L, the precision of the 10 HAAs was 0.4%–6.4% and 2.3%–6.9%, respectively, indicating that the method has good repeatability.

[0068] Spiking recovery experiments showed that the recoveries of the 10 HAAs were 88.5%–111.9% at a spike level of 1 μg / L and 86.6%–109.7% at a spike level of 10 μg / L.

[0069] The above results show that the method of the present invention has good accuracy at different concentration levels and can be used for the quantitative determination of 10 HAAs in drinking water raw water, water produced during water treatment and water leaving the treatment plant.

[0070] Example 2: In this embodiment, raw drinking water is used as the sample to be tested, and the specific steps are as follows: (1) Acidification of water sample: Add 1.5 mL of concentrated sulfuric acid to 30 mL of water sample to make the water sample under strong acidic conditions, such as pH value less than 0.5. Under this condition, HAAs in the water sample are converted from ionic state to molecular state which is more easily extracted by organic solvents, which is beneficial to subsequent liquid-liquid extraction.

[0071] (2) Salting out and liquid-liquid extraction: Add 5.5 g of anhydrous sodium sulfate to the acidified water sample and shake until fully dissolved to increase the ionic strength of the aqueous phase and promote the transfer of HAAs to the organic phase. Then add 3 mL of methyl tert-butyl ether, shake and extract for 4 min, and obtain the upper organic phase extract after standing and separating the layers.

[0072] (3) Acidified methanol esterification: Take 2 mL of the upper organic phase extract and place it in a derivatization flask. Add 2 mL of 10% (v / v) sulfuric acid-acidified methanol solution, mix well, and react in a 50°C water bath for 3 h to convert monochloroacetic acid, monobromoacetic acid, dichloroacetic acid, iodoacetic acid, trichloroacetic acid, bromochloroacetic acid, monobromodichloroacetic acid, dibromoacetic acid, monochlorodibromoacetic acid, and tribromoacetic acid into the corresponding methyl haloacetic acids. This step is used to improve the volatility and gas chromatography applicability of HAAs, enabling them to be detected by GC-ECD.

[0073] (4) Secondary salting-out phase separation: After the esterification reaction is completed, the sample is cooled at 4°C for 5 min, and then 7 mL of sodium sulfate aqueous solution with a concentration of 150 g / L is added. After shaking for 3 min, the sample is allowed to stand for phase separation. This step is used to promote the separation of the organic phase, acidified methanol phase and aqueous phase, so that the derivatized methyl haloacetate is retained in the organic phase and the influence of acidified methanol and aqueous phase residues on subsequent chromatographic detection is reduced.

[0074] (5) Neutralization of residual acid: After discarding the lower aqueous phase, add a total of 1 mL of saturated sodium bicarbonate solution in four portions to the remaining organic phase to neutralize the residual acid. Shake after each addition of sodium bicarbonate solution to release the carbon dioxide produced in the reaction. After neutralization, allow the phases to separate, and transfer the upper organic phase as the GC-ECD sample.

[0075] (6) GC-ECD separation and detection: A DB-1701 capillary column (30.0 m × 0.25 mm × 0.25 μm) was used, with high-purity nitrogen as the carrier gas. The injection port temperature was 210℃, splitless injection was used, the injection volume was 1 μL, and the column flow rate was 1.0 mL / min. The detector temperature was 300℃, and the tail gas flow rate was 30 mL / min. The column temperature program was as follows: initial temperature 42℃ held for 2 min; temperature increased to 61℃ at 2.5℃ / min; then increased to 105℃ at 8℃ / min; then increased to 205℃ at 20℃ / min and held for 5 min. Under the above chromatographic conditions, methyl ester derivatives of 10 HAAs were separated and detected, and chromatograms were obtained (e.g., chromatograms of HAAs were obtained). Figure 1 (As shown).

[0076] (7) Quantitative analysis of standard curve: Prepare a 2 mg / L HAA mixed standard solution and dilute it to obtain a series of standard solutions of 0.1 μg / L, 0.5 μg / L, 1 μg / L, 5 μg / L, 10 μg / L and 20 μg / L. Each standard solution is subjected to GC-ECD determination using the above steps (1)-(6) to establish a peak area-concentration standard curve (refer to Table 1).

[0077] (8) Chromatographic peak identification: After being processed by the method of the present invention, the 10 HAA mixed standards all produced identifiable chromatographic responses under GC-ECD conditions.

[0078] Referring to the peak area-concentration standard curve, the sample to be tested can be qualitatively and / or quantitatively analyzed based on the retention time and peak area.

[0079] Example 3: In this embodiment, water from the water production process is used as the sample to be tested. The specific steps are as follows: (1) Acidification of water sample: Add 1.5 mL of concentrated sulfuric acid to 30 mL of water sample to make the water sample under strong acidic conditions, such as pH value less than 0.5. Under this condition, HAAs in the water sample are converted from ionic state to molecular state which is more easily extracted by organic solvents, which is beneficial to subsequent liquid-liquid extraction.

[0080] (2) Salting out and liquid-liquid extraction: Add 6g of anhydrous sodium sulfate to the acidified water sample and shake until fully dissolved to increase the ionic strength of the aqueous phase and promote the transfer of HAAs to the organic phase. Then add 3 mL of methyl tert-butyl ether, shake and extract for 5 min, and obtain the upper organic phase extract after standing and separating the layers.

[0081] (3) Acidified methanol esterification: Take 2 mL of the upper organic phase extract and place it in a derivatization flask. Add 2 mL of 10% (v / v) sulfuric acid-acidified methanol solution, mix well, and react in a 50°C water bath for 2.5 h to convert monochloroacetic acid, monobromoacetic acid, dichloroacetic acid, iodoacetic acid, trichloroacetic acid, bromochloroacetic acid, monobromodichloroacetic acid, dibromoacetic acid, monochlorodibromoacetic acid, and tribromoacetic acid into the corresponding methyl haloacetic acids. This step is used to improve the volatility and gas chromatography applicability of HAAs, enabling them to be detected by GC-ECD.

[0082] (4) Secondary salting-out phase separation: After the esterification reaction is completed, the sample is cooled at 4°C for 5 min, and then 10 mL of sodium sulfate aqueous solution with a concentration of 150 g / L is added. After shaking for 3 min, the mixture is allowed to stand for phase separation. This step is used to promote the separation of the organic phase, the acidified methanol phase and the aqueous phase, so that the derivatized methyl haloacetate is retained in the organic phase and the influence of acidified methanol and aqueous phase residues on subsequent chromatographic detection is reduced.

[0083] (5) Neutralization of residual acid: After discarding the lower aqueous phase, add a total of 1.3 mL of saturated sodium bicarbonate solution in four portions to the remaining organic phase to neutralize the residual acid. Shake the mixture after each addition of sodium bicarbonate solution to release the carbon dioxide produced in the reaction. After neutralization, allow the mixture to stand and separate into layers. Transfer the upper organic phase as the sample to be tested by GC-ECD.

[0084] (6) GC-ECD separation and detection: A DB-1701 capillary column (30.0 m × 0.25 mm × 0.25 μm) was used, with high-purity nitrogen as the carrier gas. The injection port temperature was 210℃, splitless injection was used, the injection volume was 1 μL, and the column flow rate was 1.0 mL / min. The detector temperature was 300℃, and the make-up gas flow rate was 30 mL / min. The column temperature program was as follows: initial temperature 38℃ held for 2 min; temperature increased to 60℃ at 2.5℃ / min; then increased to 110℃ at 10℃ / min; then increased to 200℃ at 20℃ / min and held for 5 min. Under the above chromatographic conditions, methyl ester derivatives of 10 HAAs were separated and detected, and chromatograms were obtained (e.g., chromatograms of HAA derivatives of methyl ester were obtained). Figure 1 (As shown).

[0085] (7) Quantitative analysis of standard curve: Prepare a 2 mg / L HAA mixed standard solution and dilute it to obtain a series of standard solutions of 0.1 μg / L, 0.5 μg / L, 1 μg / L, 5 μg / L, 10 μg / L and 20 μg / L. Each standard solution is subjected to GC-ECD determination using the above steps (1)-(6) to establish a peak area-concentration standard curve (refer to Table 1).

[0086] (8) Chromatographic peak identification: After being processed by the method of the present invention, the 10 HAA mixed standards all produced identifiable chromatographic responses under GC-ECD conditions.

[0087] Referring to the peak area-concentration standard curve, the sample to be tested can be qualitatively and / or quantitatively analyzed based on the retention time and peak area.

[0088] Example 4: In this embodiment, the treated water is used as the sample to be tested, and the specific steps are as follows: (1) Acidification of water sample: Add 1.5 mL of concentrated sulfuric acid to 30 mL of water sample to make the water sample under strong acidic conditions, such as pH value less than 0.5. Under this condition, HAAs in the water sample are converted from ionic state to molecular state which is more easily extracted by organic solvents, which is beneficial to subsequent liquid-liquid extraction.

[0089] (2) Salting out and liquid-liquid extraction: 6 g of anhydrous sodium sulfate was added to the acidified water sample and shaken until fully dissolved to increase the ionic strength of the aqueous phase and promote the transfer of HAAs to the organic phase. Then 3.3 mL of methyl tert-butyl ether was added, and the mixture was shaken and extracted for 5 min. After standing and separating the layers, the upper organic phase extract was obtained.

[0090] (3) Acidified methanol esterification: Take 2 mL of the upper organic phase extract and place it in a derivatization flask. Add 2 mL of 10% (v / v) sulfuric acid-acidified methanol solution, mix well, and react in a 50°C water bath for 2 h to convert monochloroacetic acid, monobromoacetic acid, dichloroacetic acid, iodoacetic acid, trichloroacetic acid, bromochloroacetic acid, monobromodichloroacetic acid, dibromoacetic acid, monochlorodibromoacetic acid, and tribromoacetic acid into the corresponding methyl haloacetic acids. This step is used to improve the volatility and gas chromatography applicability of HAAs, enabling them to be detected by GC-ECD.

[0091] (4) Secondary salting-out phase separation: After the esterification reaction is completed, the sample is cooled at 4°C for 5 min, and then 8 mL of sodium sulfate aqueous solution with a concentration of 150 g / L is added. After shaking for 3 min, the sample is allowed to stand for phase separation. This step is used to promote the separation of the organic phase, acidified methanol phase and aqueous phase, so that the derivatized methyl haloacetate is retained in the organic phase and the influence of acidified methanol and aqueous phase residues on subsequent chromatographic detection is reduced.

[0092] (5) Neutralization of residual acid: After discarding the lower aqueous phase, add a total of 1.1 mL of saturated sodium bicarbonate solution in four portions to the remaining organic phase to neutralize the residual acid. Shake the mixture after each addition of sodium bicarbonate solution to release the carbon dioxide produced in the reaction. After neutralization, allow the mixture to stand and separate into layers. Transfer the upper organic phase as the sample to be tested by GC-ECD.

[0093] (6) GC-ECD separation and detection: A DB-1701 capillary column (30.0 m × 0.25 mm × 0.25 μm) was used, with high-purity nitrogen as the carrier gas. The injection port temperature was 210℃, splitless injection was used, the injection volume was 1 μL, and the column flow rate was 1.0 mL / min. The detector temperature was 300℃, and the make-up gas flow rate was 30 mL / min. The column temperature program was as follows: initial temperature 40℃ held for 2 min; temperature increased to 60℃ at 2.5℃ / min; then increased to 115℃ at 8℃ / min; then increased to 200℃ at 20℃ / min and held for 5 min. Under the above chromatographic conditions, methyl ester derivatives of 10 HAAs were separated and detected, and chromatograms were obtained (e.g., chromatograms of HAA derivatives of methyl ester were obtained). Figure 1 (As shown).

[0094] (7) Quantitative analysis of standard curve: Prepare a 2 mg / L HAA mixed standard solution and dilute it to obtain a series of standard solutions of 0.1 μg / L, 0.5 μg / L, 1 μg / L, 5 μg / L, 10 μg / L and 20 μg / L. Each standard solution is subjected to GC-ECD determination using the above steps (1)-(6) to establish a peak area-concentration standard curve (refer to Table 1).

[0095] (8) Chromatographic peak identification: After being processed by the method of the present invention, the 10 HAA mixed standards all produced identifiable chromatographic responses under GC-ECD conditions.

[0096] Referring to the peak area-concentration standard curve, the sample to be tested can be qualitatively and / or quantitatively analyzed based on the retention time and peak area.

[0097] In existing technologies, IAA is mainly detected by GC-MS. No GC-ECD has been found to list IAA as a target analyte. When IAA is added to the original HAA9 assay system, its retention time is similar to that of trichloroacetic acid (TCAA). Under the original programmed temperature conditions, the two are difficult to separate completely. In order to investigate the difference between the present invention and existing technologies in terms of the separation effect of IAA and other HAAs, three programmed temperature schemes were set up while keeping the other instrument conditions the same as in Example 1, as shown in Table 3.

[0098] Table 3. Three programmed heating schemes Example initial temperature Phase 1 Phase Two Phase Three Total duration 1 Keep at 40℃ for 2 min Increase the temperature to 60℃ at a rate of 2.5℃ / min. Heat up to 115℃ at a rate of 10℃ / min. Increase the temperature to 200℃ at a rate of 20℃ / min and hold for 5 min. 24.75 min 5 Keep at 40℃ for 10 min Increase the temperature by 2.5℃ / min to 65℃ Heat up to 85℃ at a rate of 10℃ / min Increase the temperature to 205℃ at a rate of 20℃ / min and hold for 7 min. 35 min 6 Keep at 40℃ for 2 min Increase the temperature to 60℃ at a rate of 2.5℃ / min. Heat up to 85℃ at a rate of 10℃ / min Increase the temperature to 200℃ at a rate of 20℃ / min and hold for 5 min. 23.25 min Example 5 used the temperature program conditions recommended by EPA 552.3 as a prior art control. Example 6 shortened the initial temperature holding time and adjusted the first-stage endpoint temperature, final temperature, and end-hold time, reducing the total analysis time from 35.00 min to 23.25 min. Experimental results showed that Example 6 significantly shortened the analysis time without significantly affecting the overall separation of other HAAs; however, IAA and TCAA were still not completely separated.

[0099] The total analysis time of this invention was 24.75 min, only 1.5 min longer than Example 6 and 10.25 min shorter than Example 5. Experimental results show that, using the method of this invention, IAA and TCAA can be well separated, while other HAAs maintain good peak elution and separation performance. Figure 1 Therefore, this invention can significantly shorten the analysis cycle while improving the separation effect of IAA and TCAA.

[0100] Under the optimized conditions of this invention, IAA exhibits identifiable chromatographic peaks and good quantitative response, with a method detection limit of 0.02 μg / L. At spiking levels of 1 μg / L and 10 μg / L, the recoveries are 96.9% and 92.3%, respectively, with relative standard deviations of 6.4% and 2.3%, respectively. These results demonstrate that by specifically optimizing the temperature-programmed conditions, this invention improves the chromatographic separation of IAA and TCAA and establishes a quantitative analysis method for IAA, enabling simultaneous quantitative determination of IAA and nine other HAAs on a GC-ECD platform.

[0101] Example 5 (EPA 552.3 Recommendation): In this embodiment, the specific steps are as follows: (1) Acidification of water sample: Add 1.5 mL of concentrated sulfuric acid to 30 mL of water sample to make the water sample under strong acidic conditions, such as pH value less than 0.5. Under this condition, HAAs in the water sample are converted from ionic state to molecular state which is more easily extracted by organic solvents, which is beneficial to subsequent liquid-liquid extraction.

[0102] (2) Salting out and liquid-liquid extraction: Add 6g of anhydrous sodium sulfate to the acidified water sample and shake until fully dissolved to increase the ionic strength of the aqueous phase and promote the transfer of HAAs to the organic phase. Then add 3 mL of methyl tert-butyl ether, shake and extract for 4 min, and obtain the upper organic phase extract after standing and separating the layers.

[0103] (3) Acidified methanol esterification: Take 2 mL of the upper organic phase extract and place it in a derivatization flask. Add 2 mL of 10% (v / v) sulfuric acid-acidified methanol solution, mix well, and react in a 50°C water bath for 2 h to convert monochloroacetic acid, monobromoacetic acid, dichloroacetic acid, iodoacetic acid, trichloroacetic acid, bromochloroacetic acid, monobromodichloroacetic acid, dibromoacetic acid, monochlorodibromoacetic acid, and tribromoacetic acid into the corresponding methyl haloacetic acids. This step is used to improve the volatility and gas chromatography applicability of HAAs, enabling them to be detected by GC-ECD.

[0104] (4) Secondary salting-out phase separation: After the esterification reaction is completed, the sample is cooled at 4°C for 5 min, and then 7 mL of sodium sulfate aqueous solution with a concentration of 150 g / L is added. After shaking for 3 min, the sample is allowed to stand for phase separation. This step is used to promote the separation of the organic phase, acidified methanol phase and aqueous phase, so that the derivatized methyl haloacetate is retained in the organic phase and the influence of acidified methanol and aqueous phase residues on subsequent chromatographic detection is reduced.

[0105] (5) Neutralization of residual acid: After discarding the lower aqueous phase, add a total of 1 mL of saturated sodium bicarbonate solution in four portions to the remaining organic phase to neutralize the residual acid. Shake after each addition of sodium bicarbonate solution to release the carbon dioxide produced in the reaction. After neutralization, allow the phases to separate, and transfer the upper organic phase as the GC-ECD sample.

[0106] (6) GC-ECD separation and detection: A DB-1701 capillary column (30.0 m × 0.25 mm × 0.25 μm) was used with high-purity nitrogen as the carrier gas. The injection port temperature was 210℃, splitless injection was used, the injection volume was 1 μL, and the column flow rate was 1.0 mL / min. The detector temperature was 300℃, and the make-up gas flow rate was 30 mL / min. The column temperature program was as follows: initial temperature 40℃ held for 10 min; temperature increased to 65℃ at 2.5℃ / min; then increased to 85℃ at 10℃ / min; then increased to 205℃ at 20℃ / min and held for 7 min. Under the above chromatographic conditions, methyl ester derivatives of 10 HAAs were separated and detected.

[0107] Example 6: In this embodiment, the specific steps are as follows: (1) Acidification of water sample: Add 1.5 mL of concentrated sulfuric acid to 30 mL of water sample to make the water sample under strong acidic conditions, such as pH value less than 0.5. Under this condition, HAAs in the water sample are converted from ionic state to molecular state which is more easily extracted by organic solvents, which is beneficial to subsequent liquid-liquid extraction.

[0108] (2) Salting out and liquid-liquid extraction: Add 6g of anhydrous sodium sulfate to the acidified water sample and shake until fully dissolved to increase the ionic strength of the aqueous phase and promote the transfer of HAAs to the organic phase. Then add 3 mL of methyl tert-butyl ether, shake and extract for 4 min, and obtain the upper organic phase extract after standing and separating the layers.

[0109] (3) Acidified methanol esterification: Take 2 mL of the upper organic phase extract and place it in a derivatization flask. Add 2 mL of 10% (v / v) sulfuric acid-acidified methanol solution, mix well, and react in a 50°C water bath for 2 h to convert monochloroacetic acid, monobromoacetic acid, dichloroacetic acid, iodoacetic acid, trichloroacetic acid, bromochloroacetic acid, monobromodichloroacetic acid, dibromoacetic acid, monochlorodibromoacetic acid, and tribromoacetic acid into the corresponding methyl haloacetic acids. This step is used to improve the volatility and gas chromatography applicability of HAAs, enabling them to be detected by GC-ECD.

[0110] (4) Secondary salting-out phase separation: After the esterification reaction is completed, the sample is cooled at 4°C for 5 min, and then 7 mL of sodium sulfate aqueous solution with a concentration of 150 g / L is added. After shaking for 3 min, the sample is allowed to stand for phase separation. This step is used to promote the separation of the organic phase, acidified methanol phase and aqueous phase, so that the derivatized methyl haloacetate is retained in the organic phase and the influence of acidified methanol and aqueous phase residues on subsequent chromatographic detection is reduced.

[0111] (5) Neutralization of residual acid: After discarding the lower aqueous phase, add a total of 1 mL of saturated sodium bicarbonate solution in four portions to the remaining organic phase to neutralize the residual acid. Shake after each addition of sodium bicarbonate solution to release the carbon dioxide produced in the reaction. After neutralization, allow the phases to separate, and transfer the upper organic phase as the GC-ECD sample.

[0112] (6) GC-ECD separation and detection: A DB-1701 capillary column (30.0 m × 0.25 mm × 0.25 μm) was used with high-purity nitrogen as the carrier gas. The injection port temperature was 210℃, splitless injection was used, the injection volume was 1 μL, and the column flow rate was 1.0 mL / min. The detector temperature was 300℃, and the make-up gas flow rate was 30 mL / min. The column temperature program was as follows: initial temperature 40℃ held for 2 min; temperature increased to 60℃ at 2.5℃ / min; then increased to 85℃ at 10℃ / min; then increased to 200℃ at 20℃ / min and held for 5 min. Under the above chromatographic conditions, methyl ester derivatives of 10 HAAs were separated and detected.

[0113] The specific embodiments of the present invention have been described in detail above, but they are merely examples, and the present invention is not limited to the specific embodiments described above. For those skilled in the art, any equivalent modifications and substitutions to the present invention are also within the scope of the present invention. Therefore, all equivalent transformations and modifications made without departing from the spirit and scope of the present invention should be covered within the scope of the present invention.

Claims

1. A method for determining haloacetic acid disinfection byproducts in drinking water, characterized in that the steps include... include: Water sample acidification procedure: Acidify the water sample to be tested to a strong acidic state; Salting out and extraction steps: Add sulfate to the acidified water sample to be tested, then add the extractant for extraction, and collect the organic phase; Esterification step: The organic phase is mixed with alcohol to react and esterify the HAAs in the water sample to be tested; Secondary salting-out step: After the esterification reaction is completed, add an aqueous sulfate solution and collect the organic phases in layers; GC-ECD Detection Procedure: The organic phase collected in layers is analyzed by GC-ECD. The GC column temperature program is as follows: 30-45℃, hold for 1-5 min; increase the temperature to 50-70℃ at a rate of 2-3℃ / min; then increase the temperature to 100-130℃ at a rate of 7-12℃ / min; then increase the temperature to 170-230℃ at a rate of 15-28℃ / min and hold for 3-8 min; obtain the chromatogram. Quantitative or qualitative analysis of HAAs was performed based on the peak area-concentration standard curve, the concentration of the sample to be tested, retention time, and peak area.

2. The method according to claim 1, characterized in that, The haloacetic acid disinfection byproducts include monochloroacetic acid, monobromoacetic acid, dichloroacetic acid, iodoacetic acid, trichloroacetic acid, bromochloroacetic acid, monobromodichloroacetic acid, dibromoacetic acid, monochlorodibromoacetic acid, and tribromoacetic acid.

3. The method according to claim 1, characterized in that, The GC column temperature program is as follows: hold at 35-40℃ for 2-3 min; increase the temperature to 60-65℃ at a rate of 2.5℃ / min; increase the temperature to 115-120℃ at a rate of 8-10℃ / min; and increase the temperature to 200-210℃ at a rate of 20-25℃ / min and hold for 5 min.

4. The method according to claim 1, characterized in that, The sulfate used in the salting-out and extraction steps is sodium sulfate, and the extractant is methyl tert-butyl ether; for every 30 ml of water sample to be tested, the weight of sulfate used is 3-10 g, and the volume of extractant used is 1-5 ml.

5. The method according to claim 1, characterized in that, The alcohol in the esterification step is methanol acidified with sulfuric acid. Every 2 ml of organic phase collected in the salting-out and extraction steps is esterified with 1-5 ml of acidified alcohol solution with a volume fraction of 5-20%. The reaction is carried out at 30-60℃ for ≥0.5 h.

6. The method according to claim 1, characterized in that, Before the second salting out, the reaction system after the esterification step is completed is cooled to 0-10℃.

7. The method according to claim 1, characterized in that, In the secondary salting-out step, the sulfate is sodium sulfate. For every 2 ml of organic phase collected from the salting-out and extraction steps, add 5-10 ml of a 100-200 g / L aqueous sulfate solution.

8. The method according to claim 1, characterized in that, After the secondary salting-out step, a residual acid neutralization step is also performed: an alkaline compound is added to the organic phase collected in the secondary salting-out to neutralize the residual acid.

9. The method according to claim 1, characterized in that, The alkaline compound is sodium bicarbonate, which is added in the form of a saturated solution.

10. The method according to claim 1, characterized in that, The conditions for the GC-ECD detection procedure are as follows: carrier gas is nitrogen; injection port temperature is 200-230℃; splitless injection, injection volume is 1 μL; column flow rate is 1.0 mL / min; detector temperature is 300℃; and make-up gas flow rate is 30 mL / min.

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