Determination of haloacetic acids by the combination of non-aqueous capillary electrophoresis and mass spectrometry

The applicability of capillary electrophoresis (CE) in combination with atmospheric pressure ionization mass spectrometry (API-MS) is demonstrated for the determination of organic acids and in particular for haloacetic acids. CE-conditions, sheath flow and MS-parameters were optimized with respect to the separation of the analytes and mass spectrometric sensitivity. CE/MS turned out to be an attractive alternative for the determination of haloacetic acids to existing methods based on GC-ECD. Employing CE/MS derivatization is not necessary which saves time and avoids possible sources of errors. In the present work the sample pre-treatment is performed by liquid-liquid extraction using methyl tert.-butyl ether as the extraction solvent. The organic phase is brought to dryness in a stream of nitrogen gas and the residue is dissolved in methanol and analyzed by CE/MS using a mixture of 2-propanol/water 80 : 20 containing triethylamine as the sheath liquid in the interface. Best results for the separation of all nine possible bromo- and chloroacetic acids together with two internal standards are obtained with a carrier electrolyte consisting of ammonium acetate/acetic acid in methanol; to resolve the strongly acidic trihaloacetic acids as well as the less acidic monohaloacetic acids, a careful optimization of the acetic acid content is necessary. The method was applied to the determination of haloacetic acids in real water samples. With optimized CE and MS conditions detection limits between 0.3 and 7.6 μg/L in the original water samples were achieved, employing a sample volume of 30 mL. Received: 4 May 1999 / Revised: 9 June 1999 / Accepted: 12 June 1999     

液-液萃取衍生气相色谱法测定饮用水中卤乙酸

建立了测定饮用水中5种卤乙酸的检测方法。水样经硫酸酸化、叔丁基甲醚萃取、硫酸-甲醇衍生化后,用气相色谱电子捕获检测器测定。5种卤乙酸平均加标回收率为74.5%~104.0%,相对标准偏差为3.1%~11.0%(n=6),最低检出限为0.3~15.3μg/L。该法适用于饮用水中卤乙酸的测定。     

Determination of haloacetic acids by the combination of non-aqueous capillary electrophoresis and mass spectrometry

The applicability of capillary electrophoresis (CE) in combination with atmospheric pressure ionization mass spectrometry (API-MS) is demonstrated for the determination of organic acids and in particular for haloacetic acids. CE-conditions, sheath flow and MS-parameters were optimized with respect to the separation of the analytes and mass spectrometric sensitivity. CE/MS turned out to be an attractive alternative for the determination of haloacetic acids to existing methods based on GC-ECD. Employing CE/MS derivatization is not necessary which saves time and avoids possible sources of errors. In the present work the sample pre-treatment is performed by liquid-liquid extraction using methyl tert.-butyl ether as the extraction solvent. The organic phase is brought to dryness in a stream of nitrogen gas and the residue is dissolved in methanol and analyzed by CE/MS using a mixture of 2-propanol/water 80?:?20 containing triethylamine as the sheath liquid in the interface. Best results for the separation of all nine possible bromo- and chloroacetic acids together with two internal standards are obtained with a carrier electrolyte consisting of ammonium acetate/acetic acid in methanol; to resolve the strongly acidic trihaloacetic acids as well as the less acidic monohaloacetic acids, a careful optimization of the acetic acid content is necessary. The method was applied to the determination of haloacetic acids in real water samples. With optimized CE and MS conditions detection limits between 0.3 and 7.6 μg/L in the original water samples were achieved, employing a sample volume of 30 mL.     

Extraction of ammonia and nitrite using modified magnetite iron oxide nanoparticles before spectrophotometric determination in different water samples

A new analytical approach was developed for the extraction and determination of ammonia and nitrite in environmental water samples involving magnetic solid-phase extraction (MSPE) with magnetite nanoparticles (MNPs) as the adsorbent. The procedure is based on the derivatisation of ammonia based on Berthelot reaction. The obtained indophenol dye was extracted using MSPE and determined spectrophotometrically at 655 ± 3 nm. Nitrite ion is determined after its reduction to ammonia in the presence of Zn/HCl. The main factors that affected the extraction efficiency were studied and optimised. The method gave calibration curves for ammonia with good linearity in the range 10–550 µg L^?1, and correlation coefficients (r) higher than 0.99. The detection and quantification limit was found to be 3.1 and 10.2 µg L^?1, respectively. The method showed good precision and accuracy, with intra- and inter-assay precisions of less than 6.6% at all concentrations. The recoveries ranged 89–105% and 88–105%, for ammonia and nitrite determination, respectively. The method was applied to the determination of the target analytes in real samples.     

饮用水中9种卤乙酸的超高效液相色谱法测定

建立了固相萃取/超高效液相色谱(SPE/UPLC)测定饮用水中9种痕量卤乙酸(HAAs)的分析方法.对固相萃取和液相色谱等分析条件进行了优化,选择Lichrolut EN固相萃取小柱富集饮用水中的HAAs,三乙胺-磷酸缓冲液和甲醇作为UPLC的流动相.在优化的分析条件下,9种卤乙酸在6min内实现基线分离,所有目标物在一定质量浓度范围内线性良好,相关系数为0.995 7～0.9999;一氯乙酸(MCAA)的检出限为10.85μg/L,其它8种化合物的检出限为0.25～0.70μg/L;除MCAA外,其它目标物在低、中、高3种加标水平的回收率为60%～106%.方法的相对标准偏差(RSD,n=5)为2.0%～5.7%.将此方法应用于我国北方某城市自来水中卤乙酸的测定,5种HAAs被检出.方法灵敏度高、简便快捷,可用于生活饮用水中痕量卤乙酸的测定.     

Trace determination of nine haloacetic acids in drinking water by liquid chromatography–electrospray tandem mass spectrometry

A simple, fast and sensitive liquid chromatography–electrospray tandem mass spectrometry method was established for trace levels of nine haloacetic acids (HAAs) in drinking water. Water samples were removed of residual chlorine by adding l-ascorbic acid, and directly injected after filtered by 0.22 μm membrane. Nine HAAs were separated by liquid chromatography in 7.5 min, and the limits of detection were generally between 0.16 and 0.99 μg/L except for chlorodibromoacetic acid (1.44 μg/L) and tribromoacetic acid (8.87 μg/L). The mean recoveries of nine target compounds in spiked drinking water samples were 80.1–108%, and no apparent signal suppression was observed. Finally, this method was applied to determine HAAs in the tap water samples collected from five waterworks in Shandong, China. Nine HAAs except for monochloroacetic acid, monobromoacetic acid, dibromochloroacetic acid and tribromoacetic acid were detected, and the total concentrations were 7.79–36.5 μg/L. The determination results well met the first stage of the Disinfectants/Disinfection By-Products (D/DBP) Rules established by U.S.EPA and Guidelines for Drinking-water Quality of WHO.     

Sensitive Determination of Five Priority Haloacetic Acids by Electromembrane Extraction with Capillary Electrophoresis

A method for sensitive determination of five priority haloacetic acids in drinking water has been developed for the first time based on electromembrane extraction (EME) prior to CZE with capacitively coupled contactless conductivity detection (CZE‐C⁴D). The target analytes were extracted from 10 mL of the sample solution (donor phase), through the supported liquid membrane (using a polypropylene membrane supporting 1‐octanol), and into 10 µL of 50 mmol/L NaAc solution (acceptor phase). The extracted solution was directly analyzed by CZE‐C⁴D without derivatization. Several factors that affect separation, detection and extraction efficiency were investigated. Under the optimum conditions, five haloacetic acids (monochloroacetic acid, dichloroacetic acid, trichloroacetic acid, monobromoacetic acid, and dibromoacetic acid) could be well separated from other components coexisting in water samples within 23 min, exhibiting a linear calibration over two orders of magnitude (r?0.9943); the enrichment factors at 430–671 were obtained in a 30 min of extraction, and the limits of detection were in the range of 0.17–0.61 ng/mL. The intraday relative standard deviations for peak areas investigated at 10 ng/mL were between 1.2% and 9.7% for the combined EME‐CZE‐C⁴D procedure. This approach offers an attractive alternative to the officially proposed method for purified drinking water analysis, which requires derivatization procedure prior to gas chromatography analysis.     

Spectrophotometric determination of trace-level bromate in drinking water after post-column reaction with pararosaniline based on multi-walled carbon nanotubes

A simple and sensitive spectrophotometric method is described for low level determinationof bromate in drinking water. This method is based on the reduction of bromate ions into bromine in the presence of pararosaniline by sodium metabisulphite to form a highly stable pink-red complex measured at 540 nm. Maximum colour formation was obtained at about 45 min. Multi-walled carbon nanotubes, a solid phase extraction sorbent, has been described for the removal of cationic interferences of major elements and heavy metals from water samples prior to conducting the assay. Bear’s law is obeyed in the range of 5–80 µg.L^?1 with limit of detection of 0.44 µg.L^?1 and correlation coefficient of 0.998 (n = 5). The mean relative standard deviation (RSD%) of the results within-day precision and accuracy were ≤1.2% which confirmed the reproducibility of the assay technique. The optimum assay conditions and their applicability to the determination of water samples are described. The method was successfully applied for the determination of bromate in water samples with satisfactory results and recommended to be applied in all desalination plant samples.     

Determination of haloacetic acids in water using layered double hydroxides as a sorbent in dispersive solid‐phase extraction followed by liquid chromatography with tandem mass spectrometry

In the present study, highly efficient and simple dispersive solid‐phase extraction procedure for the determination of haloacetic acids in water samples has been established. Three different types of layered double hydroxides were synthesized and used as a sorbent in dispersive solid‐phase extraction. Due to the interesting behavior of layered double hydroxides in an acidic medium (pH?4), the analyte elution step was not needed; the layered double hydroxides are simply dissolved in acid immediately after extraction to release the analytes which are then directly introduced into a liquid chromatography with tandem mass spectrometry system for analysis. Several dispersive solid‐phase extraction parameters were optimized to increase the extraction efficiency of haloacetic acids such as temperature, extraction time and pH. Under optimum conditions, good linearity was achieved over the concentration range of 0.05–100 μg/L with detection limits in the range of 0.006–0.05 μg/L. The relative standard deviations were 0.33–3.64% (n = 6). The proposed method was applied to different water samples collected from a drinking water plant to determine the concentrations of haloacetic acids.     

A comprehensive chromatographic comparison of amphetamine and methylamphetamine extracted from river water using molecular imprinted polymers and without the need for sample derivatization

This work explores the differences between two GCMS instruments for the determination of amphetamine and methylamphetamine extracted from water samples (ultra pure water and river water) without the necessity for derivatization. The instruments contained different generations of gas chromatograph and mass selective detector components and revealed significantly different results when presented with the same samples. The extraction methodology also compared two SPE systems. The extraction efficiency of commercially available molecular imprinted polymers as a sorbent in SPE was compared with commonly used hydrophilic balance sorbent. Molecular imprinted polymers provided excellent recoveries (81 ± 2% and 108 ± 3% at 30 μg L^?1, and 94 ± 2% and 94 ± 2% at 200 μg L^?1 for amphetamine and methylamphetamine, respectively). The best LOD obtained was sufficient for the determination of both drugs extracted from river water (0.029 ± 0.003 and 0.015 ± 0.004 μg L^?1 for amphetamine and methylamphetamine, respectively). These were comparable to literature values obtained through conventional extraction and analysis using LC‐MS/MS but had the advantage of being achieved using an underivatized GCMS method.     

Large‐volume sample stacking with polarity switching for analysis of azo dyes in water samples by capillary electrophoresis

ABSTRACT

A simple, fast and efficient on-line pre-concentration method (large-volume sample stacking) by capillary electrophoresis was proposed for determination of azo dyes residues (allura red [AR], sunset yellow [SY] and tartrazine [TAR]) in water samples. Pre-concentration variables involved in the system were optimised using of a Box–Bhenken design. Under the optimal conditions: injection time 150.0 s, pre-concentration time 120.0 s and reverse potential ?8.0 kV, the proposed methodology improved the analytical sensibility achieving limits of detection of 21.0–41.4 µg L^?1 with enrichment factors of 82.1–210.8 fold. The large-volume sample stacking-capillary electrophoresis method was validated and applied to determine azo dyes residues in 20 water samples (bottled, spring and tap water). Two samples were positive for sunset yellow and tartrazine with a concentration of 25.3 and 30.2 µg L^?1 and % RSD less than 10.0% in all cases.     

水中卤乙酸类化合物测定方法的研究进展

卤乙酸为饮用水消毒副产物,对人体具有毒害作用,目前受到国内外研究者的重视。对饮用水中卤乙酸的检测标准和测定方法的研究进展进行了综述。     

A new HPIC-UV method to quantify phenolic acids in food and environmental samples

A simple and rapid HPIC method has been developed for the separation and quantification of nine phenolic acids (PAs): gallic acid, syringic acid, vanillic acid, sinapic acid, ferulic acid, p-coumaric acid, protocatechuic acid, caffeic acid and ellagic acid. Separation was carried out on an Dionex Ion-Pac AS-11 (250 mm × 4 mm I.D.) column with a Dionex Ion-Pac AG-11 (50 mm × 4 mm I.D) guard column. Elution was performed using 1000 mM sodium hydroxide (NaOH) and 500 mM sodium acetate (NaOAc) in a multi step binary gradient at a flow rate of 1 mL min^?1. Detection was performed using diode array detector set at 230, 250, 280, and 330 nm. After optimisation of various parameters, the separation of the nine phenolic acids was achieved within 23 minutes with a good resolution. Peak areas for each compound showed good linearity (R2 > 0.999) in a relatively wide concentration range. Detection limits were in the range of 10–530 µg L^?1 at a signal-to-noise ratio 3 : 1 and the amount of phenolic acids determined were in the range 0.20–10.0 ng when 20 µl of sample was injected. The developed procedure was successfully applied for the determination of these compounds in food (green tea, tomato juice and wine samples) and environmental samples (soil, surface water, organic fertiliser, organic waste) with minimal sample preparation. Beside good performances (separation, resolution, sensitivity and linearity), the new method is very fast and not expensive which makes it interesting for both scientific research and routine analysis of food and environmental samples.     

High performance ion chromatography of haloacetic acids on macrocyclic cryptand anion exchanger

A new high performance ion chromatographic method has been developed for the separation of the nine chlorinated-brominated haloacetic acids (HAAs) that are the disinfection by-products of chlorination of drinking water, using a macrocycle-based adjustable-capacity anion-exchange separator column (IonPac Cryptand A1). A gradient method based on theoretical and experimental considerations has been optimized in which 10 mM NaOH-LiOH step gradient was performed at the third minute of the analysis. The optimized method allowed us to separate the nine HAAs and seven possibly interfering inorganic anions in less than 25 min with acceptable resolution. The minimum concentrations detectable for HAAs were between 8.0 (MBA) and 210 (TBA) microg L(-1), with linearity included between 0.9947 (TBA) and 0.9998 (MBA). To increase sensitivity, a 25-fold preconcentration step on a reversed phase substrate (LiChrolut EN) has been coupled. Application of this method to the analysis of haloacetic acids in real tap water samples is illustrated.     

Simultaneous determination of trace oxyhalides and haloacetic acids using suppressed ion chromatography-electrospray mass spectrometry

A new analytical procedure for the simultaneous determination of trace oxyhalides and haloacetic acids (HAs) in drinking water and aqueous soil extracts is described. The method uses micro-bore ion chromatography (IC) coupled with suppressed conductivity (SC) and electrospray ionization mass spectrometric detection (ESI-MS). The IC-SC-ESI-MS system included a secondary flow of 100% MeOH, which was added to the column eluate (post-suppressor) and resulted in a significant increase in sensitivity for all analytes. All ESI-MS parameters were optimized for HA analysis and sensitivity quantitatively compared to suppressed conductivity. Full analytical performance characteristics for the developed method are presented for monochloro-, monobromo-, dichloro-, dibromo-, trichloro-, bromochloro, chlorodifluoro-, trifluoro-, dichlorobromo- and dibromochloroacetic acid, as well as the oxyhalides iodate, bromate, chlorate and perchlorate. In the case of the HAs, an optimised 25-fold SPE preconcentration method meant all analytes could be readily detected well below the USEPA 60 μg/L regulatory limit using conductivity and/or ESI-MS. The IC-ESI-MS method was applied to the determination of oxyhalides and HAs in both soil extracts and drinking water samples. Soil samples were extracted using ultra pure water with subsequent determination of perchlorate at 1.68 μg/g of soil. A drinking water sample containing HAs was preconcentrated using LiChrolut EN solid phase extraction cartridges with subsequent sulphate and chloride removal. Total HAs were determined at 13 μg/L.     

SPE-GC-MS for the Determination of Halogenated Acetic Acids in Drinking Water

The development and optimization of analytical methods for the better monitoring of disinfection by-products especially haloacetic acids in water are key step in order to estimate human exposure to such products after chlorination. A reliable and accurate analytical method is needed in order to reach the levels of concentration required by United States Environmental Protection Agency regulations. In this study a method was developed for determining halogenated acetic acids in drinking water, involving solid phase extraction, methylation derivatization, and GC-MS. The new SPE-GC-MS-SIM method is capable of analyzing all nine acids at extremely low μg L^–1 level. Run time is significantly reduced without compromising analytical results. The major advantages of the method are the simplicity of the chromatography, short run time and low detection limits. The method performance, limits of detection and spiking recovery were evaluated and the results proved that the accuracy and precision were good. This method outperforms previous GC-MS methods especially for the determination of dibromoacetic, dibromochloroacetic, dichlorobromoacetic and tribromoacetic acids. The method has been used to analyse domestic tap water and water samples collected at a local water treatment plant.     

Negative ion electrospray of bromo- and chloroacetic acids and an evaluation of exact mass measurements with a bench-top time-of-flight mass spectrometer

The negative ion electrospray mass spectra of six bromo- and chloroacetic acids were measured using two different electrospray interfaces and single quadrupole and bench-top time-of-flight mass spectrometers. With each acid at 50 μg/mL in aqueous methanol at pH 10, the anions observed included deprotonated molecules, adducts, and fragment ions. With each acid at 100 ng/mL in aqueous acetonitrile at pH 10, mainly deprotonated molecules are observed. The exactm/z measuring capability of the time-of-flight mass spectrometer was evaluated to assess the potential for the determination of the individual acids in mixtures without an on-line separation. Mean measurement errors were nearly always less than ± 9 ppm and the majority were less than ± 5 ppm. Potential interferences by substances having similar exact masses and the ability to form anions in aqueous solutions were evaluated. The estimated detection limits of the five regulated haloacetic acids in drinking water, without a sample preconcentration step, are in the range of 24–86 ng/mL, which is within about a factor of 10 of the levels required for routine monitoring of the acids. Actual drinking water samples were not analyzed pending the development of slightly more sensitive techniques and quantitative analytical procedures.     

On-line monitoring of nine haloacetic acid species at the μg L level using post-column reaction-ion chromatography with nicotinamide fluorescence

A laboratory-built automated instrument is reported for on-line, near real-time monitoring of nine haloacetic acids species (HAA9) in drinking water. The device uses anion-exchange chromatography to separate the HAA9 species, followed by post-column reaction with nicotinamide in basic solution with fluorescence detection. Method detection limits for HAA9 species ranged from 0.6 to 10.1 μg L⁻¹, mean % recovery values ranged from 58 to 161%, and % relative standard deviation ranged from 3.5 to 32% while operating within a factor of 2.5-5 of the method detection limit. The bias between the proposed method and United States Environmental Protection Agency Method 552.3 was measured during two separate on-line studies and using grab samples collected from different distribution systems. In general, the two methods showed good agreement with biases for HAA9 of less than 10 μg L⁻¹.     

In situ derivatization and hollow fiber membrane microextraction for gas chromatographic determination of haloacetic acids in water

An alternative method for gas chromatographic determination of haloacetic acids (HAAs) in water using direct derivatization followed by hollow fiber membrane liquid-phase microextraction (HF-LPME) has been developed. The method has improved the sample preparation step according to the conventional US EPA Method 552.2 by combining the derivatization and the extraction into one step prior to determination by gas chromatography electron captured detector (GC-ECD). The HAAs were derivatized with acidic methanol into their methyl esters and simultaneously extracted with supported liquid hollow fiber membrane in headspace mode. The derivatization was attempted directly in water sample without sample evaporation. The HF-LPME was performed using 1-octanol as the extracting solvent at 55 °C for 60 min with 20% Na₂SO₄. The linear calibration curves were observed for the concentrations ranging from 1 to 300 μg L⁻¹ with the correlation coefficients (R²) being greater than 0.99. The method detection limits of most analytes were below 1 μg L⁻¹ except DCAA and MCAA that were 2 and 18 μg L⁻¹, respectively. The recoveries from spiked concentration ranged from 97 to 109% with %R.S.D. less than 12%. The method was applied for determination of HAAs in drinking water and tap water samples. The method offers an easy one step high sample throughput sample preparation for gas chromatographic determination of haloacetic acids as well as other contaminants in water.     

Retention profile of Fe,Mn and Cu onto chemically treated polyurethane with carbon disulfide

Dithiocarbamate modified polyurethane foam (DTC-PUF) was synthesized as a new solid-phase extraction sorbent for the preconcentration and determination of Fe(II), Mn(II) and Cu(II) in environmental samples using flame atomic absorption spectrometry. Maximum extraction of the elements was achieved at pH 5–7 and flow rate 3 mL min^?1. Quantitative desorption was achieved by 10 mL from 1.0 mol L^?1 HCl solution. The capacity of the sorbent was 149.2 ± 0.5, 237.5 ± 0.2, 200.2 ± 0.1 μg g^?1 and the limit of detection was of 0.015, 0.015 and 0.012 μg mL^?1for Fe(II), Mn(II) and Cu(II), respectively. A preconcentration factor of 100 was obtained for all elements. The developed method was successfully applied to the determination of the tested elements in water (tap and lake) and plant (spinach and parsley leaves) samples and showed good recovery values from 98 to 111% with corresponding RSD values ranged from 0.6 to 8.6%.