Dispersive Liquid-Liquid Microextraction Coupled to Gas Chromatography-Electron Capture Detection for the Analysis of Trihalomethane Formation Potential

Dispersive liquid-liquid microextraction (DLLME) is an attractive miniaturized technique that utilizes microliter volumes of extraction solvents. In this study, a DLLME technique was employed for the determination of four major trihalomethane (THM) compounds and analyzed using gas chromatography-electron capture detection. Optimization was conducted in terms of type and volume of disperser solvent, type and volume of extraction solvent, and addition of salt and extraction time. Optimized conditions employed methanol (0.25 mL) as the disperser solvent containing carbon disulfide (20 µL) as the extraction solvent. The linear range was 0.020–4.00 µg/L. Low limits of detection for the analytes were obtained in the range of 0.01 to 0.24 µg/L with enrichment factors ranging from 95–283. The relative recoveries of THMs from water samples at spiking level of 2 µg/L were in the range of 79.9 to 103.4%. This method was successfully applied to the determination of THM formation potential (THMFP) in river water samples. It was found that the concentration of THMFP in three Malaysian rivers were below the maximum permissible limits of World Health Organization (WHO).     

Natural organic matter removal by coagulation during drinking water treatment: A review

Natural organic matter (NOM) is found in all surface, ground and soil waters. An increase in the amount of NOM has been observed over the past 10-20 years in raw water supplies in several areas, which has a significant effect on drinking water treatment. The presence of NOM causes many problems in drinking water and drinking water treatment processes, including (i) negative effect on water quality by causing colour, taste and odor problems, (ii) increased coagulant and disinfectant doses (which in turn results in increased sludge volumes and production of harmful disinfection by-products), (iii) promoted biological growth in distribution system, and (iv) increased levels of complexed heavy metals and adsorbed organic pollutants. NOM can be removed from drinking water by several treatment options, of which the most common and economically feasible processes are considered to be coagulation and flocculation followed by sedimentation/flotation and sand filtration. Most of the NOM can be removed by coagulation, although, the hydrophobic fraction and high molar mass compounds of NOM are removed more efficiently than hydrophilic fraction and the low molar mass compounds. Thus, enhanced and/or optimized coagulation, as well as new process alternatives for the better removal of NOM by coagulation process has been suggested. In the present work, an overview of the recent research dealing with coagulation and flocculation in the removal of NOM from drinking water is presented.     

Supported capillary membrane sampling-gas chromatography on a valve with a pulsed discharge photoionization detector

The objective of this study was to develop and evaluate a simple miniaturized approach to gas chromatography termed supported capillary membrane sampling-gas chromatography on a valve (SCMS-GCOV). The prototype instrument uses a pulsed discharge photoionization detector (PDPID) as the GC detector. Two different analyzers were constructed. The first used a bench scale SCMS-GC. The second was a miniaturized SCMS-GCOV analyzer. The SCMS-GCOV analyzer was used to monitor the concentrations of trihalomethanes (THM4) in drinking water. Details are given for the construction of the SCMS-GC-PDPID and the SCMS-GCOV-PDPID analyzers. The results of method detection limit, accuracy and precision studies are reported for analysis of THM4 and are compared to other methods of THM4 analysis. Side-by-side comparison studies are conducted between the SCMS-GCOV and USEPA 502.2 with promising results.     

Application of liquid-phase microextraction to the analysis of trihalomethanes in water

A liquid-phase microextraction method for the determination of trihalomethanes (THMs) including chloroform (CHCl₃), bromodichloromethane (CHBrCl₂), dibromochloromethane (CHBr₂Cl) and bromoform (CHBr₃) in water samples was developed, with analysis by gas chromatography-electron capture detection (GC-ECD). After the determination of the most suitable solvent and stirring rate for the extraction, several other parameters (solvent drop volume, extraction time and ionic strength of the sample) were optimized using a factorial design to obtain the most relevant variables. The optimized extraction conditions for 5 mL of sample volume in a 10 mL vial were as follows: n-hexane an organic solvent; a solvent drop volume of 2 μL; an extraction time of 5.0 min; a stirring rate of 600 rpm at 25 °C; sample ionic strength of 3 M sodium chloride. The linear range was 1-75 μg L⁻¹ for the studied THMs. The limits of detection (LODs) ranged from 0.23 μg L⁻¹ (for CHBr₂Cl) to 0.45 μg L⁻¹ (for CHCl₃). Recoveries of THMs from fortified distilled water were over 70% for a fortification level of 15 μg L⁻¹, and relative standard deviations of the recoveries were below 5%. Real samples collected from tap water and well water were successfully analyzed using the proposed method. The recovery of spiked water samples was from 73% to 78% with relative standard deviations below 7%.     

Sonochemical removal of trihalomethanes from aqueous solutions

In this research, ultrasound irradiation was employed to degrade the trihalomethanes, THMs: CHCl₃, CHBrCl₂, CHBr₂Cl, CHBr₃, and CHI₃. The kinetics reaction rates and removal efficiencies of the THMs compounds, as a sole component in the aqueous solutions, were studied. Batch experiments were conducted at an ultrasonic frequency of 20 kHz and acoustic intensity of 3.75 W/cm². The first-order degradation rate constants and the sonolysis efficiencies followed the decreasing order of CHCl₃ > CHBrCl₂ > CHBr₂Cl > CHBr₃ > CHI₃. Up to 100% of the CHCl₃ was removed, while only 60% of the CHI₃ was sonodegraded, after 180 min sonication. The THMs vapor pressure was found to be the most important parameter affecting the sonodegradation kinetics and efficiency, while the bond dissociation energy and hydrophilic/hydrophobic characteristics of the THMs compounds were found to be of secondary importance.     

Study of Br,Zn, Cu and Fe concentrations in healthy and cancer breast tissues by TXRF

Tissue samples of fifteen breasts were analyzed by X-ray fluorescence spectrometry in order to compare the elemental concentration in healthy and carcinoma regions of the same individual. Five women were from Germany and ten from Portugal living in big cities. The elemental distribution of P, S, K, Ca, Fe, Ni, Zn, Cu and Br present in both normal and cancerous breast tissues were studied. Several contiguous thin sections (up to 10 μm thickness) of each tissue were analyzed by TXRF in order to study the homogeneity in the elemental concentration along each tissue. Correlations between elemental concentrations were established.     

Development of a sensitive thermal desorption method for the determination of trihalomethanes in humid ambient and alveolar air

A sensitive and reliable method has been developed for the determination of trihalomethanes (THMs) in air samples through adsorption in sorbent tubes and thermal desorption (TD) of the compounds, followed by gas chromatography (GC)–mass spectrometry (MS) analysis. Three commercial sorbent materials were compared in terms of adsorption efficiency and breakthrough volume, finding Chromosorb 102 to be the most appropriate adsorbent for air sampling. The method allows us to reach detection limits of 0.03 ng (0.01 μg m⁻³ for 3 l of air), linear ranges from 0.1 to 2000 ng and specific uncertainties of ca. 5.0 ± 0.2 ng for all THMs. Several salts were tested to reduce water retention (from the humid air of an indoor swimming pool) at the sampling stage, Na₂SO₄ being the one that provides optimum efficiency. The method was validated by a new recovery study in which several tubes with and without adsorbent were spiked with THMs and analyzed by TD-GC/MS, recoveries ranging from 92% to 97% for all the compounds. Finally, the performance of the method was evaluated through the analysis of ambient air samples from an indoor swimming pool and alveolar air samples from swimmers to assess their THM uptake. THMs were found to be stable in the sorbent tubes for at least 1 month when stored at 4 °C.     

A comparison of three solvent-free techniques coupled with gas chromatography for determining trihalomethanes in urine samples

The analysis of volatile organic compounds in samples of biological fluids characterized by complex matrices is highly challenging. This paper presents a comparison of the results obtained in this field using three solvent-free techniques: thin-layer headspace with autogenous generation of liquid sorbent (TLHS) and membrane separation of the trace substances (pervaporation, PV), both of which are coupled to direct aqueous injection gas chromatography–electron capture detection (TLHS–DAI–GC–ECD and PV–DAI–GC–ECD), as well as conventional static headspace analysis followed by GC analysis with ECD detection (HS–GC–ECD). Basic validation parameters of the HS–GC–ECD, TLHS–DAI–GC–ECD and PV–DAI–GC–ECD procedures were calculated for water and urine samples. The calibration curves for all procedures were linear within the concentration range examined. The intermediate precisions of the procedures were good and reached about 10% (for all analytes) for HS–GC–ECD and TLHS–DAI–GC–ECD. The poorest results were obtained for PV–DAI–GC–ECD: about 20% for all analytes. The lowest method detection limits were obtained for the TLHS–DAI–GC–ECD procedure: below 0.0022 μg/L for all analytes. The enrichment factors did not differ significantly between water and urine samples, indicating little or no matrix effect in all procedures.     

HS-SPME-GC/MS测定饮用水中三卤甲烷分析条件的优化

对顶空固相微萃取 -气相色谱 /质谱联用测定饮用水中三卤甲烷的分析条件如固相微萃取的萃取时间、萃取温度、溶液的离子强度及 p H值等进行了优化。该方法的线性范围为 5— 15 0 μg/ L,相对标准偏差为 5 .4 %— 8.2 %。     

色氨酸与消毒剂反应形成三卤甲烷的光谱分析

使用荧光光谱和紫外光谱分析消毒剂(自由氯,自由溴)和色氨酸的反应及消毒副产物三卤甲烷的产生特性。实验表明：消毒剂反应降低了色氨酸荧光强度和FRI值(fluorescence region integration),二者线性相关。消毒剂中自由溴比例增加,荧光团FRI降低,UV₂₈₀值降低,UV₂₅₄值增加。THMs中溴代产物比例也随自由溴比例单调增加,而THMs总量没有呈现相似的变化规律。反映出和自由氯相比,自由溴取代性更强而氧化性更弱。自由溴单独和色氨酸反应时,FRI与CHBr₃产生量线性相关。加入NH₃后,消毒剂性质改变使得线性被破坏。