On-line monitoring of trihalomethanes in drinking water using continuous-flow purge and cryofocusing gas chromatography-mass spectrometry

A continuous-flow purge-and-trap-GC-MS system was developed for on-line monitoring of THMs (trihalomethanes) in drinking water. Three systems with different traps and purging flow-rates are discussed. In order to minimize interference from water vapor, total purge gas volume and injection temperature were controlled during analysis. Shorter sample concentration time and GC separation time reduced total cycle time to less than 5 min. The detection limits of the system could be lowered to 10 ppt, 25 ppt, 40 ppt, and 50 ppt (w/w) for CHCl3, CHCl2Br, CHClBr2, and CHBr3, respectively. This system could detect changes in sample concentration when applied to the on-line monitoring of THMs in drinking water.     

气相色谱法直接进样测定饮用水中挥发性卤代烃

 利用大口径毛细管柱气相色谱/电子捕获检测器(GC/ECD)方法,直接进样测定了饮用水中的三氯甲烷、四氯化碳、一溴二氯甲烷、二溴一氯甲烷、三溴甲烷等5种挥发性卤代烃。所建立的方法简便、快速、灵敏度高,并具有较好的精密度与准确度。当5种卤代烃化合物的质量浓度平均值为9.03～20.19μg/L时,CV为2.9%～7.5%,标准差为0.3～0.9μg/L。样品的加标回收率为80%～118%,标准曲线的相关系数为0.998和0.999。ECD的温度为350℃时,其最低检测限在0.1～0.7μg/L范围内,均低于文献报道值 。     

Automated measurement and calibration of reactive volatile halogenated organic compounds in the atmosphere

The automated calibration and analysis of very low mixing ratios of the reactive volatile organic halocarbons CH(3)I, CHCl(3), C(2)H(5)I, 2-C(3)H(7)I, CH(2)Br(2), CH(2)ClI, CHBr(2)Cl, 1-C(3)H(7)I, CH(2)BrI, CHBr(3) and CH(2)I(2) for long term atmospheric field measurements are described. Analytes were pre-concentrated from 3 l of air onto an adsorbent trap cooled to -10 [degree]C using Peltier plates, and rapidly transferred to a gas chromatograph (GC) by resistive heating. A two stage Carboxen 1016/Carbotrap C adsorbent trap allowed good analyte recovery and rapid desorption without the need for post-desorption cryofocussing. Halocarbons were detected using a mass spectrometer (MS) in selective ion mode. Detection limits were between 0.02 and 0.12 pptv (parts per trillion by volume) for approximately hourly samples of CHCl(3), CH(3)I, C(2)H(5)I, 1-C(3)H(7)I, 2-C(3)H(7)I, CH(2)ClI, CH(2)Br(2), CHBr(2)Cl, CH(2)BrI, CHBr(3) and CH(2)I(2) with a precision of 3-8%. A novel calibration system was constructed which utilised fixed volume (50 [micro sign]l) injections of the output of thermostatted permeation tubes into a stream of nitrogen gas in order to dilute parts per million by volume (ppmv) mixing ratios into pptv. The calibration was completely automated, allowing multi-point calibrations during routine operation. The overall accuracy of the measurements is estimated to be +/-15%. The instrument was used continuously for automated atmospheric measurements during a 4-month research cruise from Germany to Antarctica, and a 6 week field campaign at Mace Head, Ireland. The results for CHCl(3) during the latter campaign were within 13% of measurements made by a GC-MS operating continuously at the site within the long term Advanced Global Atmospherics Gases Experiment.     

Quantum yields for Cl(2P(j)) atom formation from the photolysis of chlorofluorocarbons and chlorinated hydrocarbons at 193.3 nm

Cl(2P(3/2)) and Cl*(2P(1/2)) atoms produced from the photodissociation of chlorofluorocarbons (CFCs) and chlorinated hydrocarbons at 193.3 nm have been detected quantitatively by a technique of vacuum ultraviolet laser-induced fluorescence (VUV-LIF) spectroscopy at 135.2 and 134.7 nm for j = 1/2 and 3/2, respectively. The quantum yields for total Cl-atom formation in the 193.3 nm photolysis at 295 +/- 2 K have been determined to be 1.03 +/- 0.09, 1.01 +/- 0.08, 1.03 +/- 0.08, 1.03 +/- 0.10, 1.41 +/- 0.14, 1.02 +/- 0.08, and 0.98 +/- 0.08 for CF2Cl2, CFCl3, CH2Cl2, CHCl3, CCl4, CHFCl2, and CCl3CF3, respectively. Those results suggest that the single C-Cl bond rupture always occurs in the photolysis of these molecules except for CCl4. Formation of two Cl atoms partly takes place in the photodissociation of CCl4. The quantum yields for total Cl-atom formation in the 193.3 nm photolysis of CHBr2Cl and CHBrClCF3 are 0.27 +/- 0.02 and 0.28 +/- 0.02, respectively, which suggests that the C-Br bond rupture is a main channel in the photodissociation processes. The branching ratios between the spin-orbit states, Cl*(2P(1/2)) and Cl(2P(3/2)), have also been determined for the photodissociation of the chlorinated compounds at 193.3 nm. The UV photodissociation processes giving rise to formation of Cl(2P(j)) atoms from the chlorinated compounds studied here have been discussed.     

高级氧化技术矿化水中三氯甲烷和二氯甲烷理论极限浓度分析

对环境安全性尤其是饮用水安全而言,通常认为的高级氧化技术(AOPs)"彻底降解"大多数有毒有机污染物的观点需应用化工热力学分析来检验.本文分别以三氯甲烷(CHCl3)和二氯甲烷(CH2Cl2)为模型体系,分析了不同氯代甲烷初始浓度、pH值和羟基自由基(·OH)浓度下,AOPs矿化水中氯代甲烷的平衡浓度(即矿化理论极限浓度).结果表明,CHCl3和CH2Cl2与·OH矿化反应的理论极限浓度均随着初始浓度的增加而增加,随着·OH浓度的增加而明显减小;CHCl3与·OH矿化反应的理论极限浓度随着pH值的增加而明显减小(pH3.0～3.5除外),CH2Cl2与·OH矿化反应的理论极限浓度在文献报道的·OH浓度下随着pH值的增加无明显变化,而在·OH浓度分别增至文献值的10和100倍时,CH2Cl2与·OH矿化反应的理论极限浓度随着pH值由2.0增至3.0和由3.5增至4.5而不断减小,由3.0增至3.5和由4.5增至5.0而增加.较高的·OH浓度,较高pH值(pH4.0～5.0)的酸性环境以及较低的初始浓度对氯代甲烷的彻底矿化更有利.     

On-line monitoring by membrane introduction mass spectrometry of chlorination of organics in water. Mechanistic and kinetic aspects of chloroform formation

Chloroform formation during the chlorination of simple organic molecules modeling humic substances, such as phenol and di- and trihydroxybenzenes, was studied by on-line membrane introduction mass spectrometry (MIMS). Under the reaction conditions employed, chloroform was rapidly formed from 1,3-dihydroxybenzene, 1, 4-dihydroxybenzene, phenol and 1,2,3-trihydroxybenzene with yields of 17, 13, 7 and 5%, respectively. With the exception of aniline, which afforded a 17% chloroform yield, non-phenolic compounds, such as nitrobenzene, chlorobenzene, toluene, benzene and cyclohexanol, furnished low yields. Mechanistic studies showed that phenol is chlorinated consecutively and produces initially chlorophenol. It is suggested that chloroform might be formed mainly from chlorinated 3, 5-cyclohexadienone-type intermediates. MIMS was also used to determine the reaction rates and to study the kinetics of the chlorination. A good Hammett linear correlation for an electrophilic substitution mechanism was found for the compounds C(6)H(5)X (X = NH(2), OH, CH(3), H, Cl and NO(2)).     

Methods validation for the determination of trihalomethanes in drinking water

Trihalomethanes (THMs), chlorinated by-products in drinking water, have been determined by comparing some analytical methods, based on the following techniques: liquid-liquid extraction-gas chromatography-mass spectrometry (LLE-GC-MS), headspace-gas chromatography-mass spectrometry (headspace-GC-MS) and purge and trap-gas chromatography-mass spectrometry (PT-GC-MS). The mass spectrometer was operated in the SIM mode. The quantitative methods were validated and compared to the ability to identify and to measure reliably the yields of the toxic compounds. Good validation parameters were obtained for each method.     

Polar symmetry in new high-pressure phases of chloroform and bromoform

Polar ordering has been induced by pressure in solid chloroform (trichloromethane), CHCl3, and bromoform (tribromomethane), CHBr3, obtained by isochoric and isothermal freezing in a diamond anvil cell. Structures of these new polymorphs have been determined by single-crystal X-ray diffraction, CHCl3 at 0.62 and 0.75 GPa and CHBr3 at 0.20 and 0.35 GPa. Despite different centrosymmetric structures of all low-temperature phases of CHCl3 (space group Pbcn) and CHBr3 (P6(3)/m, P1, and P3), the high-pressure phases are isostructural in space group P6(3). The polar phase of CHBr3 is formed at 295 K, already at the freezing pressure of approximately 0.1 GPa, while CHCl3 transforms from the Pbcn phase into the P6(3) phase between 0.62 and 0.75 GPa. It has been demonstrated that the electrostatic contribution to halogen...halogen and H...halogen interactions in the CHCl3 and CHBr3 molecular crystals is favorable for the polar aggregation and that this effect intensifies with increasing pressure.     

Use of InCl(3) as a cocatalyst and a Cl(2)Pd(DPEphos)-P(2-furyl)(3) catalyst system for one-pot hydrometalation-cross-coupling and carbometalation-cross-coupling tandem processes

One-pot conversion of alkynes to regio- and stereodefined alkenylmetals containing Al and Zr via hydrometalation or carbometalation followed by their Pd-catalyzed cross-coupling with (E)-ICH=CHBr or (E)-ICH=CHCl proceeds cleanly and selectively to give the corresponding 1-halo-1,3-dienes in excellent yields using a catalyst system consisting of Cl(2)Pd(DPEphos), DIBAL-H, and TFP (catalyst A) with InCl(3) as a cocatalyst.     

Structural analysis and Fourier transform infrared and Raman spectra of dibutoxyphosphoryl benzylisothiourea

A structural analysis for dibutoxyphosphoryl benzylisothiourea (DBBT) was carried out by mass spectrometry, 1H NMR, 13C NMR, infrared and Raman spectroscopy. The Fourier transform infrared and Fourier transform Raman spectra of liquid of DBBT were carried out with the purpose of studying the tautomerism (structures I and II) and the behavior of the more polar absorption's bands in different solvents, i.e., absorption's of the P=O and C=N bands. The results suggest the existence of tautomerism in the pure (liquid) compound and in solution of CHCl(3), CH(2)Cl(2), CHBr(3), and THF, C(2)H(4)Cl(2) and C(2)H(4)Br(2). The solvent interaction with the P=O band was characterized by the presence of a new band in the region of the O-H absorption. A vibrational assignment of the IR bands and Raman shifts was done and is proposed in this paper.     

Coupled LC-GC-MS for on-line clean-up,separation, and identification of chlorinated polycyclic aromatic hydrocarbons at picogram levels in urban air

Coupled liquid chromatography – gas chromatography – mass spectrometry (LC-GC-MS) has been applied for on-line clean up, separation, and identification of chlorinated polycyclic aromatic hydrocarbons (CI-PAHs). A loop-type interface was used to couple the liquid chromatograph on-line with the GC-MS, and concurrent solvent evaporation was used for sample transfer. A back-flush technique was used in conjunction with a two-dimensional column system for isolation of CI-PAHs and polycyclic aromatic hydrocarbons (PAHs). This fraction was transferred on-line to the GC and separated on a capillary column. Selective and sensitive detection of CI-PAHs in the GC eluate was obtained by negative ion chemical ionization (NICI) mass spectrometry and selected ion monitoring (SIM). The combined on-line system for isolation, separation, and identification showed high precision and accuracy, and demonstrated a linear response from 1 to 1000 pg for chlorinated PAHs. The estimated detection limit was 250 fg for 1-chloropyrene and 1,6-dichloropyrene. The technique was demonstrated by analysis of urban air samples. The low detection limit made it possible to use the technique for analysis of personally carried monitoring equipment for measurement of exposure to CI-PAHs in the work environment.     

New derivatization method for determination of 3-chloro-4(dichloromethyl)-5-hydroxy-2(5H)-furanone in water

An extremely potent mutagen, 3-chloro-4(dichloromethyl)-5-hydroxy-2(5H)-furanone (MX) is commonly present in chlorinated drinking water. Due to its high mutagenic activity and according to World Health Organization guidelines its concentration should be controlled in drinking waters. Determination of MX is difficult due to ppt levels at which the compound usually exists in drinking waters. Derivatization of MX with 2-propanol is presented as a method which significantly lowers the GC–MS detection level compared to other alcohol derivatization agents.     

FTIR study of the Cl- and Br-atom initiated oxidation of trichloroethylene

The Cl- and Br- initiated oxidations of CHCl(DOUBLEBOND)CCl₂ in 700 torr of air at 296 K have been studied using a Fourier transform infrared spectrometer. Rate constants k(Cl+CHCl(DOUBLEBOND)CCl₂)=(7.2±0.8)×10⁻¹¹ and k(Br+CHCl(DOUBLEBOND)CCl₂)=(1.1±0.4)×10⁻¹³ cm³ molecule⁻¹ s⁻¹ were determined using a relative rate technique with ethane and ethylene as references, respectively. The major products observed were CHXClC(O)Cl, (X=Cl or Br), CHClO, and CCl₂O. Combining results obtained for the Cl-initiated oxidation of CHCl₂(SINGLEBOND)CHCl₂, we deduced that Cl-addition on trichloroethylene occurs via channel 1a, Cl+CHCl(DOUBLEBOND)CCl₂→ CHCl₂(SINGLEBOND)CCl₂, (100±12)%. Self-reaction of the subsequently generated peroxy radicals CHCl₂(SINGLEBOND)CCl₂O₂ leads to CHCl₂CCl₂O radicals which were found to decompose via channel 8a, CHCl₂C(O)Cl+Cl, (91±11)% of the time, and channel 8b, CHCl₂+CCl₂O, (9±2)%. The reaction Br+CHCl(DOUBLEBOND)CCl₂→CHBrCl(SINGLEBOND)CCl₂ (17a) accounted for ≥(96±11)% of the total reaction. Decomposition of the CHBrCl(SINGLEBOND)CCl₂O radicals proceeds (≥93±11)% via CHBrClC(O)Cl+Cl. As part of this work, k(Cl+CHCl₂C(O)Cl)=(3.6±0.6)×10⁻¹⁴ and k(Cl+CHCl₂(SINGLEBOND)CHCl₂)=(1.9±0.2)×10⁻¹³ cm³ molecule⁻¹ s⁻¹ were measured. Errors reported above include statistical uncertainties (2σ) and estimated systematic uncertainties. © 1997 John Wiley & Sons, Inc. Int J Chem Kinet: 29: 695–704, 1997.     

On-line flow injection analysis of volatile organic compounds in seawater by membrane introduction mass spectrometry

The combination of flow injection analysis with membrane introduction mass spectrometry for analysis of volatile organic compounds (VOCs) in seawater is examined and is compared to measurements made in water. Membrane introduction mass spectrometry is performed using a benchtop ion trap mass spectrometer, and characterization of various aspects of the flow injection and ion trap combination for the analysis of volatile organic compounds (including anthropogenic halocarbons) in seawater is carried out. The analyte responses are shown to be linear over several orders of magnitude (e.g. for methylene chloride), independent of seawater pH (e.g. for chlorobenzene) and independent of matrix effects for the VOCs studied. A comparison of the performance of a microporous (Teflon) membrane with that of an amorphous silicone membrane is made, and the former is shown to provide lower detection limits which are in the parts-per-trillion range (300 ppt for chlorobenzene, 190 ppt for trans-1,2-dichloroethene). The microporous membrane provides faster response times by a factor of four to five for relatively more polar compounds, such as chlorobenzene. An analysis of a seven-component mixture demonstrates the ability of this on-line combination to allow multicomponent analysis of mixtures of some complexity.     

Detection of chlorinated methanes by tin oxide gas sensors

Tin oxide thin films prepared by thermal oxidation of Sn films were used for the detection of chlorinated methanes (CH2Cl2, CHCl3 and CCl4). This resulted in better chemical selectivity, sensitivity, response speed and detection limit than seen with previous detectors. The temperature dependence of the sensing of 1% CCl4 gas was studied and the best sensing behavior was observed at 300 degrees C. The films showed different chemical selectivity in both speed and direction of sensing response to each gas and were stable for more than 3 weeks under operating conditions. The films showed rapid gas sensing (<40 s to reach 90% of full response) and low detection limits (< 4 ppm CCl4). The role of oxygen in the detection of chlorinated methanes and in resistance changes without chlorinated methanes was also studied. The changes at the surface of the film after gas sensing were examined using scanning electron microscopy with energy-dispersive X-ray spectrometry.     

On-line monitoring of chloramine reactions by membrane introduction mass spectrometry

Membrane introduction mass spectrometry has been applied to on-line monitoring of the reaction of monochloramine with hydrogen chloride. The detection limit for monochloramine introduced by a sheet-membrane direct-insertion probe and measured by electron impact ionization and selected ion detection was found to be 0.7 mg/l. Formation of dichloramine, trichloramine and molecular chlorine in response to the addition of hydrogen chloride to the monochloramine solution was measured on-line. The flow-through membrane introduction mass spectrometry method for detection of chloramines and characterization of their chemistry has minimal memory effects, high molecular specificity, high speed of analysis owing to fast response times, and low detection limits.     

On-line purge and trap gas chromatography for monitoring of trihalomethanes in drinking water distribution systems

A method using an automated on-line purge and trap gas chromatograph with a dry electrolytic conductivity detector (DELCD) has been developed for monitoring four regulated trihalomethanes in drinking water distribution systems. This analyzer samples trihalomethanes from drinking water by pervaporation through a silicone capillary membrane contained within a gas extraction cell (GEC) followed by preconcentration using an adsorbent trap. Trihalomethanes are subsequently desorbed from the trap onto a capillary column, separated and detected. The analyzer operates in real-time, samples directly from the drinking water distribution system and is fully automated. The optimization, operation, and evaluation of the analyzer and method are discussed. Method detection limits (MDL) are less than 1.0 μg L⁻¹ with acceptable estimates for accuracy, and precision. The results from two on-line monitoring studies in chlorinated and chloraminated distribution systems are presented. The performance of the method is compared directly to United Stated Environmental Protection Agency Method 502.2 and shows a very slight, but acceptable bias.     

Determination of triazine herbicides in surface and drinking waters by off-line combination of liquid chromatography and gas chromatography-mass spectrometry

Summary Mass spectra of 12 triazines were obtained by electron impact (EI), positive-ion chemical ionization (PCI) and negative-ion chemical ionization (NCI) using methane and isobutane as reagent gases. EI mass spectrometry is more sensitive than PCI and NCI, although the chemical ionization modes increase selectivity markedly. A pre-column packed with polymer stationary phase was employed to preconcentrate surface and drinking water samples. After desorption of the analytes with ethyl acetate, an aliquot was injected directly into the GC-MS system. Atrazine and simizine were found in these samples at 10–80 ppt levels. The limits of detection for both herbicides were below 10 ppt in drinking water.     

A long-lived C2H3ClBr* radical from the reaction of atomic chlorine with vinyl bromide

The reaction of Cl with CH₂CHBr produces both CH₂CHCl and (with HI present) CH₂ClCH₂Br in pressure-dependent yields, indicating a long-lived (?10^?10s) C₂H₃ClBr* precursor to CH₂CHCl. The precursor structure(s) may be CH₂ClCHBr* and/or CH₂CHClBr*, probably the latter with a 1,2-Br shift included in the mechanism. The addition reaction itself may not be very “anti-Markownikoff”, gaining that appearance by the subsequent 1,2-halogen shift.