Volatile organo-halogen trace analysis in beverages by thin-layer headspace enrichment and electron-capture gas-chromatography

Applicability of thin-layer headspace (TLHS) procedure giving an aqueous concentrate and also classical purge and trap (PT) in off-line mode to isolate and enrich volatile organohalogen compounds in common beverages was tested. Both enrichment tech-niques were used in combination with gas chromatography – electron capture detection (GC-ECD). TLHS, combined with direct aqueous injection (DAI)-GC-ECD, proved applicable in the determination of volatile organohalogen compounds in all studied beverages, while the PT in a version with no preliminary sample pre-treatment was of limited applicability. Detection limits of the TLHS-based procedure were in the order of 1 ppt. Content of volatile organohalogen compounds in a number of beverages available on the Polish market including mineral waters, beers, juices, carbonated and non-carbonated soft drinks, etc. was determined by means of TLHS-DAI-GC-ECD.     

管网中的饮用水消毒副产物研究进展

控制管网中消毒副产物生成是研究热点,对管网消毒副产物变化规律进行研究,可为控制管网消毒副产物提供指导。在管网中,余氯、季节变化和管材是影响管网消毒副产物的重要因素,余氯量越大,THMs和HAAs的量就越多;季节变化主要会影响化学作用和微生物活性,消毒副产物的生成速率随温度的升高而显著加快,夏秋生成的消毒副产物更多,春冬生成的消毒副产物相对少一些;铁管的腐蚀能使消毒副产物增加,但产生的Fe2＋也能使部分消毒副产物被还原。HAAs与AOC前体物间具有相似性,含量呈正相关性,存在较好的线形关系。     

咸潮对氯消毒中三卤甲烷的影响

受咸潮影响的出厂水三卤甲烷比非咸潮时高5倍,其中三溴甲烷增加10~4倍,远远大于三氯甲烷,4种THM8含量顺序发生了倒置,即CHBr_3>CHBr_2Cl>CHBrCl_2>CHCl_3。在管网中咸潮污染的出厂水和未污染水混合,加之余氯的作用,使得管网水中三卤甲烷(THMs)的种类分配再次发生变化。结合国内外的资料,综合评述了咸潮中溴化物与氯的反应及Br-THMs形成的机理,并提出了在咸潮期间控制饮用水中氯化消毒产物的思路。     

氨基糖氯消毒后典型卤代碳、氮消毒副产物生成势研究

本研究以典型氨基糖类物质D-(+)-葡萄糖胺为研究对象,采用氯消毒方式,探究了D-(+)-葡萄糖胺是否是卤代碳、氮消毒副产物三卤甲烷(THMs)和三氯硝基甲烷(TCNM)的前驱物,明确其THMs和TCNM生成势及投氯量、p H值、溴离子浓度、亚硝酸根离子浓度这对其生成势的影响。结果表明:D-(+)-葡萄糖胺是THMs和TCNM的主要前驱物,三氯甲烷是氯消毒过程中主要的THMs物种。增大投氯量,HNMs和TCNM的生成势均升高;随着p H值的增大,THMs的生成势升高,TCNM的生成势先升高后降低;随着溴离子浓度和亚硝酸根离子浓度的增大,THMs的生成势均为先升高后降低,而TCNM生成势在高溴离子和高亚硝酸根离子浓度下则表现出被抑制的趋势。     

Thermal stability of chloroform in the steam-condensate cycle of CANDU-PHW nuclear power plant

Analysis of samples taken at the Gentilly 2 (Québec) CANDU-PHW (CANadian Deuterium Uranium - Pressurized Heavy Water) plant after chlorination and demineralization revealed the presence of all four trihalomethanes (THMs) (CHCl₃, CHBrCl₂, CHBr₂Cl and CHBr₃) and other unidentified halogenated volatile compounds. Among the THMs, chloroform was the major contaminant. A study of its thermal stability in water at different temperatures confirmed the degradation of the CHCl₃ molecule according to the equation CHCl₃ + H₂O → CO + 3 HCl. The reaction follow a first order kinetics and has an activation energy of 100 kJ/mol. The estimated half-life is six seconds at 260°C, the maximum temperature of the steam-condensate cycle.     

An analytical method for the analysis of trihalomethanes in ambient air using solid‐phase microextraction gas chromatography‐mass spectrometry: An application to indoor swimming pool complexes

A simple method for the collection and analysis of the four brominated and chlorinated trihalomethanes (THMs) in air samples is described. Ambient air samples were collected in pre‐prepared glass vials, with THM analysis performed using solid‐phase microextraction gas chromatography‐mass spectrometry, where the need for chemical reagents is minimized. Analytical parameters, including oven temperature program, solvent volume, incubation time, vial agitation, extraction time and temperature, as well as desorption time and temperature, were evaluated to ensure optimal method performance. The developed method allows for point‐in‐time quantification (compared to an average concentration measured over extended periods of time), with detection limits between 0.7 to 2.6 µg/m³. Excellent linearity (r² > 0.99), repeatability (3% to 11% RSD), and reproducibility (3% to 16% RSD) were demonstrated over a concentration range from 2 to 5000 µg/m³. The method was validated for the analysis of THMs in indoor swimming pool air and was used to investigate the occurrence of THMs in the air above 15 indoor swimming pools. This is the first study to report the occurrence of THMs in swimming pool air in Australia, and concentrations higher than those previously reported in other countries were measured.     

Reaction processes effecting the analysis of chloroform by direct aqueous injection gas chromatography

Several important reaction processes which influence the analysis of chloroform by direct aqueous injection (DAI) gas chromatography have been identified through an investigation of the chlorination reactions of humic acid and a series of simple polyhydroxyaromatic and diketone model compounds in dilute solution. The reaction of chlorine with each substrate system was studied over the pH range 2–12. Gas chromatographic analysis by the DAI and organic solvent liquid-liquid extraction (LLE) procedures gave different measurements for the yield of CHCl₃ depending on the pH of the reaction solution and the chemical structure of the substrate. Under acidic and neutral conditions, a variety of trichloromethyl-substituted intermediates were identified at high concentrations in addition to chloroform by GC/MS. Chloral hydrate, trichloroacetic acid, pentachloroacetone and hexachloroacetone undergo hydrolysis and/or decarboxylation to form CHCl₃ at the high injection port temperatures employed in aqueous injection GC analysis. The results obtained in the current study indicate that the decomposition of these and structurally-related species accounts for differences previously observed upon application of the DAI and either the LLE or purge-and-trap techniques for the determination of CHCl₃ in chlorinated natural waters.     

珠江源水中THMFP的分子质量分布及其特征研究

以珠江广州段水源水为研究对象，采用超滤分离方法将其中的有机物分成分子质量不同的几种形态，考察了各分子质量组分在DOC、UV、THMFP等方面的差异。结果表明：①分子质量在3～10ku间的有机物是珠江广州段源水中最主要的THMs前驱物；②分子质量最小（〈1ku）的组分，尽管SUVA值最低，THMs生成能力（THMFP／DOC）却最强；③经超滤分离有机物量的损失很少，但紫外吸收明显减弱，THMs生成量也随之减少。     

消毒副产物形成的影响因素研究

在含有腐殖酸的水样中加入邻苯二酚进行氯化试验,分析pH值、氯化时间、温度和投氯量等因素对生成消毒副产物的影响,结果表明：随着pH值的升高,三卤甲烷的浓度逐渐增大而卤乙酸的浓度逐渐降低;三卤甲烷和卤乙酸的浓度随氯化时间的延长而增大;高温条件下三卤甲烷和卤乙酸的生成能力均大于低温条件;在一定范围内随着投氯量增加,三卤甲烷和卤乙酸的生成量也不断增加.