Headspace liquid-phase microextraction of trihalomethanes in drinking water and their gas chromatographic determination

In the present work, a novel method for the determination of trihalomethanes (THMs) such as chloroform, dichlorobromomethane, chlorodibromomethane and bromoform in drinking water has been described. It is based on coupling headspace liquid-phase microextraction (HS-LPME) with gas chromatography-electron capture detector (GC-ECD). A microdrop of organic solvent at the tip of a commercial microsyringe was used to extract analytes from aqueous samples. Three organic solvents—xylene, ethylene glycol and 1-octanol—were compared and 1-octanol was the most sensitive solvent for the analytes. Extraction conditions such as headspace volume, extraction time, stirring rate, content of NaCl and extraction temperature were found to have significant influence on extraction efficiency. The optimized conditions were 15 ml headspace volume in a 40 ml vial, 10 min extraction time and 800 rpm stirring rate at 20 °C with 0.3 g ml⁻¹ NaCl. The linear range was 1-100 μg l⁻¹ for THMs. The limits of detection (LODs) ranged from 0.15 μg l⁻¹ (for dichlorobromomethane and chlorodibromomethane) to 0.4 μg l⁻¹ (for chloroform); and relative standard deviations (RSD) for most of THMs at the 10 μg l⁻¹ level were below 10%. Real samples collected from tap water and well water were successfully analyzed using the proposed method. The recovery of spiked water samples was from 101 to 112%.     

Determination of the steroid hormone levels in water samples by dispersive liquid-liquid microextraction with solidification of a floating organic drop followed by high-performance liquid chromatography

In this study, the steroid hormone levels in river and tap water samples were determined by using a novel dispersive liquid-liquid microextraction method based on the solidification of a floating organic drop (DLLME-SFO). Several parameters were optimized, including the type and volume of the extraction and dispersive solvents, extraction time, and salt effect. DLLME-SFO is a fast, cheap, and easy-to-use method for detecting trace levels of samples. Most importantly, this method uses less-toxic solvent. The correlation coefficient of the calibration curve was higher than 0.9991. The linear range was from 5 to 1000 μg L⁻¹. The spiked environmental water samples were analyzed using DLLME-SFO. The relative recoveries ranged from 87% to 116% for river water (which was spiked with 4 μg L⁻¹ for E1, 3 μg L⁻¹ for E2, 4 μg L⁻¹ for EE2 and 9 μg L⁻¹ for E3) and 89% to 102% for tap water (which was spiked with 6 μg L⁻¹ for E1, 5 μg L⁻¹ for E2, 6 μg L⁻¹ for EE2 and 10 μg L⁻¹ for E3). The detection limits of the method ranged from 0.8 to 2.7 μg L⁻¹ for spiked river water and 1.4 to 3.1 μg L⁻¹ for spiked tap water. The methods precision ranged from 8% to 14% for spiked river water and 7% to 14% for spiked tap water.     

Preparation and properties of a new solid state borate ion selective electrode and its application

A new borate ion selective electrode using solid salts of Ag₃BO₃, Ag₂S and Cu₂S has been developed. Detailed information is provided concerning the composition, working pH and conditioning of the electrode. An analytically useful potential change occurred from 1 × 10⁻⁶ to 1 × 10⁻¹ M borate ion. The slope of the linear portion was 31 ± 2 mV/10-fold changes in borate concentration. The measurements were made at constant ionic strength (0.1 M NaNO₃) and at room temperature. The effect of Cl⁻, Br⁻, NO₃⁻, SO⁼₄, H₂PO₄⁻ anions and K⁺, Na⁺, Cu²⁺, Ag⁺, Ca²⁺ cations on borate response is evaluated and it was found that only Ag⁺ had a small interference effect. The lifetime of the electrode was more than two years, when used at least 4-5 times a day, and the response time was about 20-30 s. Borate content in waste water of borax factory, tap water of a town situated near to the borax factory and city tap water far from these mines were also determined. The validation was made with differential pulse polarography for the same water sample, and high consistency was obtained.     

Solid phase extractive preconcentration coupled to gas chromatography-atomic emission detection for the determination of chlorophenols in water samples

Solid-phase extraction (SPE) followed by derivatization and gas chromatography-atomic emission detection (GC-AED) was evaluated for the determination of five chlorophenols (CPs) in water samples. The derivatization was based on the esterification of phenolic compounds with ferrocenecarboxylic acid. The determination of the derivatized phenols was performed by GC-AED in the iron selective detection mode at 302 nm. The described method was tested on spiked water samples.The overall method gave detection limits of 1.6-3.7 ng L⁻¹ and recoveries of 90.9-104.5% for the examined mono- to trichlorophenols in 10 mL water samples. The CPs extracted from a 10 mL water sample with SPE were concentrated into 100 μL of organic solvent, a preconcentration factor of 100. The method was applied to lake and tap water samples, and CP contents between 6 and 51 ng L⁻¹ in lake water and between below the detection limit and 8 ng L⁻¹ in tap water were found for different CPs. The method is quick, simple and gives excellent recoveries, limits of detection and standard deviations.     

Solid-state pH nanoelectrode based on polyaniline thin film electrodeposited onto ion-beam etched carbon fiber

An ultramicro pH sensor has been constructed based on a thin polyaniline film that was electrochemically deposited onto a carbon fiber nanometer-size electrode. The substrate nanoelectrodes were fabricated using ion-beam conically etched carbon fibers with tip diameters ranging ca. from 100 to 500 nm. The polyaniline film was deposited from HCl solution containing the aniline monomer by cycling the potential between −0.2 and +1.0 V. The electromotive force (emf) signal between the pH sensitive polyaniline-coated nanoelectrode and an Ag/AgCl reference electrode was linear over the pH range of 2.0-12.5 with a slightly super-Nernstian slope of ca. −60 mV/pH unit. Response times ranged from several sec at pHs around 7 up to 2 min at pH 12.5. The proposed pH nanoelectrode displayed high ion selectivity with respect to K⁺, Na⁺, Ca²⁺, and Li⁺, with log K_H,M values around −12 and has a working lifetime of about 20 days. Key parameters important for the pH nanoelectrode performance, including polyaniline film preparation, selectivity, response time, temperature dependence, relative coating thickness, stability, and reproducibility, have been characterized and optimized. The performance of the pH nanoelectrode was examined by measuring the pH of several real samples including body fluids (serum, urine) and low ionic strength water samples (rain, deionized and tap water). The results agreed very well with those obtained by using commercial glass pH electrodes. The proposed pH nanoelectrode demonstrated attractive properties and seems particularly promising for use under physiological conditions.     

Preconcentration/preelution ion chromatography for the determination of perchlorate in complex samples

The determination of perchlorate in complex matrices by ion chromatography (IC) with an online preconcentration and preelution technique is discussed. The method was applied to different sample types containing large concentrations of matrix anions that would otherwise interfere with analysis via conventional IC. The present approach was highly effective in removing most of the matrix anions and was thus resistant to the interferences commonly encountered in a high ionic strength background. Method performance was evaluated by analyzing for low-level perchlorate in synthetic high ionic strength solutions, tissue extracts, and hydroponic nitrate fertilizer samples. Not only is it easier to practice the present method compared to USEPA Method 314.0, but for most of these samples the present approach provided equal to or better recovery of perchlorate than Method 314.0. With a sample of specific conductance 12,650 μS cm⁻¹, for example, the present method provided a perchlorate recovery of 101% at the 25 μg L⁻¹ level versus 89% by EPA Method 314.0. Method detection limits of perchlorate in hydroponic fertilizer samples with this method (130-190 μg kg⁻¹) are the lowest thus far reported.     

Formation of halogenated by-products of parabens in chlorinated water

Chemical transformations of four alkyl esters of p-hydroxybenzoic acid, parabens, in chlorinated water samples are investigated. Quantification of the parent species and identification of their reaction by-products were performed using gas chromatography in combination with mass spectrometry. Experiments were accomplished considering free chlorine and paraben concentrations at the mg L⁻¹ and μg L⁻¹ level, respectively. Concentration of water samples, using solid-phase extraction, and silylation of the target species were carried out in order to improve the detectability of parent species and their possible transformation products, achieving quantification limits at the low ng L⁻¹ level. Under employed experimental conditions, the decrease in the concentrations of parabens followed pseudo-first-order kinetics. Half-lives values obtained for model ultrapure water solutions were in good agreement with those observed in tap water samples. For the first type of sample, only two by-products were detected for each paraben. They corresponded to chlorination of the aromatic ring in one or two carbons situated in ortho-positions to the hydroxyl group. Both species were also generated after the addition of parabens to chlorinated tap water. Moreover, three new transformation products were noticed for each parent compound. They were identified as bromo- and bromochloro-parabens, formed due to the existence of traces of bromide in tap water sources. Experiments carried out by mixing paraben-containing personal care products with tap water, containing free chlorine, confirmed the formation of all above described halogenated by-products. In addition, the presence of the di-chlorinated forms of methyl and propyl paraben has been detected for first time in raw sewage water samples.     

Liquid chromatographic determination of microcystins in water samples following pre-column excimer fluorescence derivatization with 4-(1-pyrene)butanoic acid hydrazide

A method to measure the concentrations of microcystins (MCs) in water samples has been developed by incorporating pre-column fluorescence derivatization and liquid chromatography (LC). A solid-phase extraction for pretreatment was used to extract the MCs in water samples. The MCs were derivatized with excimer-forming 4-(1-pyrene)butanoic acid hydrazide (PBH). The MCs could then be detected by fluorescence after separation with a pentafluorophenyl (PFP)-modified superficially porous (core shell) particle LC column. The derivatization reactions of MCs with PBH proceeded easily in the presence of 4,6-dimethoxy-1,3,5-triazin-2-yl-4-methylmorpholinium (DMT-MM) as a condensation reagent, and the resulting derivatives could be easily separated on the PFP column. The derivatives were selectively detected at excimer fluorescence wavelengths (440–540 nm). The instrument detection limit and the instrument quantification limit of the MCs standards were 0.4–1.2 μg L⁻¹ and 1.4–3.9 μg L⁻¹, respectively. The method was validated at 0.1 and 1.0 μg L⁻¹ levels in tap and pond water samples, and the recovery of MCs was between 67 and 101% with a relative standard deviation of 11%. The proposed method can be used to quantify trace amounts of MCs in water samples.     

Determination of non-ionic and anionic surfactants in environmental water matrices

Solid-phase extraction (SPE) combined with liquid chromatography electrospray mass spectrometry (LC-(ESI)MS) was used to determine 16 non-ionic and anionic surfactants in different environmental water samples at ng L⁻¹ levels. The proposed method is sensitive and simple and has good linear range and detection limits (less than 50 ng L⁻¹) for most compound classes.The effect of ion suppression was studied in aqueous matrices from several treatment plants—including urban and industrial wastewater treatment plants (WWTPs), drinking-water treatment plants (DWTPs) and seawater desalination plants (SWDPs)—and it was considered when quantifying our samples. In addition, conventional treatments and tertiary treatments that use advanced membrane technologies, such as ultrafiltration (UF) and reverse osmosis (RO) were evaluated in order to determine their efficiency in eliminating these compounds.The concentrations of non-ionic surfactants in the raw waters studied ranged from 0.2 to 100 μg L⁻¹. In effluents, the concentrations ranged from 0.1 to 5 μg L⁻¹, which reflects consistent elimination. Anionic surfactants were present in all waters studied at higher levels. Levels up to 3900 μg L⁻¹ of linear alkylbenzene sulfonates (LASs) and 32,000 μg L⁻¹ of alkyl ethoxysulfates (AESs) were detected in urban WWTP influents, while levels up to 25 μg L⁻¹ of LASs and 114 μg L⁻¹ of AESs were found in drinking-water and desalination treatment plants.The results indicate that conventional processes alone are not sufficient to completely remove the studied surfactants from waste streams. Tertiary treatments that use advanced membrane technologies such as UF and RO can further reduce the amount of target compounds in the effluent water.     

Preparation of a new solid state fluoride ion selective electrode and application

A new solid state fluoride ion selective electrode composed of 70% Ag₂S, 10% Cu₂S and 20% CaF₂ has been developed. An analytically useful potential change occurred, from 1 × 10⁻⁶ to 1 × 10⁻¹ M fluoride ion. The slope of the linear portion (1 × 10⁻¹-1 × 10⁻⁵ M) was about 26 ± 2 mV/10-fold concentration changes in fluoride. It was found that pH change between 1 and 8 had no effect on the potential of the electrode. There was no interference of most common cations such as K^+, Na⁺, Ca²⁺ and Mg²⁺ and anions such as Cl⁻, NO₃⁻, SO₄²⁻ and PO₄³⁻. The lifetime of the electrode was more than 2 years, when used at least 4-5 times a day, and the response time was about 60 s.The measurements were made at constant ionic strength (0.1 M NaNO₃) and at room temperature. This electrode has been used for the determination of fluoride ion in Ankara city tap water and in bottled spring water using standard addition method. The validation of the electrode has been made with a commercial fluoride ion selective electrode (Orion) and high consistency was obtained.     

New use of polypyrrole-chloride for selective preconcentration of copper prior to its determination of flame atomic absorption spectrometry

Polypyrrole-chloride was studied as a new sorbent for preconcentration of copper(II) using solid-phase extraction prior to determination by flame atomic absorption spectrometry. The sorbent showed an extremely high selectivity towards copper(II) as an anionic chelate, i.e. Cu (pyrocatechol violet)₂²⁻ in the pH range of 4-7. Copper(II) as Cu (pyrocatechol violet)₂²⁻ was selectively retained on a column containing 1.0 g of polypyrrole-chloride and quantitatively eluted by 3 mL of 2.0 mol L⁻¹ nitric acid. The calibration graph was linear with a correlation coefficient of 0.999 at levels near the detection limit and up to at least 50 μg L⁻¹. When applied for preconcentration and determination of copper in tap water, waste water and hot spring water, the recoveries were found to be 96, 101 and 95%, respectively, with high precision (% relative standard deviation <4%) and low detection limit (0.87 μg L⁻¹). Verification of the accuracy was carried out by the analysis of a standard reference material (BCR 715 wastewater-SRM). The relative error was +3.33%. The proposed method was successfully applied to the determination of copper in tap water, waste water and hot spring water samples.     

A rapid and sensitive analytical method for the determination of 14 pyrethroids in water samples

A simple, efficient and environmentally friendly analytical methodology is proposed for extracting and preconcentrating pyrethroids from water samples prior to gas chromatography-negative ion chemical ionization mass spectrometry (GC-NCI-MS) analysis. Fourteen pyrethroids were selected for this work: bifenthrin, cyfluthrin, λ-cyhalothrin, cypermethrin, deltamethrin, esfenvalerate, fenvalerate, fenpropathrin, τ-fluvalinate, permethrin, phenothrin, resmethrin, tetramethrin and tralomethrin. The method is based on ultrasound-assisted emulsification-extraction (UAEE) of a water-immiscible solvent in an aqueous medium. Chloroform was used as extraction solvent in the UAEE technique. Target analytes were quantitatively extracted achieving an enrichment factor of 200 when 20 mL aliquot of pure water spiked with pyrethroid standards was extracted. The method was also evaluated with tap water and river water samples. Method detection limits (MDLs) ranged from 0.03 to 35.8 ng L⁻¹ with RSDs values ≤3–25% (n = 5). The coefficients of estimation of the calibration curves obtained following the proposed methodology were ≥0.998. Recovery values were in the range of 45–106%, showing satisfactory robustness of the method for analyzing pyrethroids in water samples. The proposed methodology was applied for the analysis of river water samples. Cypermethrin was detected at concentration levels ranging from 4.94 to 30.5 ng L⁻¹.     

The defluoridation of drinking water using multi-walled carbon nanotubes

In this study, the potential sorption capacity of multi-walled carbon nanotubes (MWCNTs) was investigated as a means of removing fluoride from the drinking water of a number of regions in Iran and from experimental solutions. The test was conducted in both batch and continuous operation modes. Batch mode experiments were used to study the effect of parameters such as pH, contact time, ionic strength, adsorbent dose, adsorbent capacity, and the presence of foreign anions on the efficiency of fluoride removal. The results showed that the highest level of sorption occurs at pH 5 (about 94% at 18 min). The ionic strength of the solutions and the presence of co-anions such as chloride, nitrate, sulfate, hydrogen carbonate, perchlorate had a negligible effect on the sorption of F⁻ onto MWCNTs. Sorption capacity measurements revealed that MWCNTs have a saturation capacity of 3.5 mg of F⁻ per gram. Sorption data were best fitted with the Fruendlich sorption isotherm equation, which indicates that F⁻ tends to be adsorbed on MWCNTs in a multilayered manner. Experiments using Kohbanan city drinking water, which contains the highest level of F⁻ among the drinking water samples studied, showed that MWCNTs can remove over 85% of fluoride content.     

Headspace solid-phase microextraction using a dodecylsulfate-doped polypyrrole film coupled to ion mobility spectrometry for the simultaneous determination of atrazine and ametryn in soil and water samples

A simple and rapid headspace solid-phase microextraction (HS-SPME) based method is presented for the simultaneous determination of atrazine and ametryn in soil and water samples by ion mobility spectrometry (IMS). A dodecylsulfate-doped polypyrrole (PPy-DS), synthesized by electrochemical method, was applied as a laboratory-made fiber for SPME. The HS-SPME system was designed with a cooling device on the upper part of the sample vial and a circulating water bath for adjusting the sample temperature. The extraction properties of the fiber to spiked soil and water samples with atrazine and ametryn were examined, using a HS-SPME device and thermal desorption in injection port of IMS. Parameters affecting the extraction efficiency such as the volume of water added to the soil, pH effect, extraction time, extraction temperature, salt effect, desorption time, and desorption temperature were investigated. The HS-SPME-IMS method with PPy-DS fiber, provided good repeatability (RSDs < 10 %), simplicity, good sensitivity and short analysis times for spiked soil (200 ng g⁻¹) and water samples (100 and 200 ng mL⁻¹). The calibration graphs were linear in the range of 200-4000 ng g⁻¹ and 50-2800 ng mL⁻¹ for soil and water respectively (R² > 0.99). Detection limits for atrazine and ametryn were 37 ng g⁻¹ (soil) and 23 ng g⁻¹ (soil) and 15 ng mL⁻¹ (water) and 10 ng mL⁻¹ (water), respectively. To evaluate the accuracy of the proposed method, atrazine and ametryn in the three kinds of soils and two well water samples were determined. Finally, comparing the HS-SPME results for extraction and determination of selected triazines using PPy-DS fiber with the other methods in literature shows that the proposed method has comparable detection limits and RSDs and good linear ranges.     

Sensitive determination of cadmium in water samples by room temperature ionic liquid-based preconcentration and electrothermal atomic absorption spectrometry

A sensitive preconcentration methodology for Cd determination at trace levels in water samples was developed in this work. 1-Butyl-3-methylimidazolium hexafluorophosphate ([C₄MIM][PF₆]) room temperature ionic liquid (RTIL) was successfully used for Cd preconcentration, as cadmium-2-(5-bromo-2-pyridylazo)-5-diethylaminophenol complex [Cd-5-Br-PADAP]. Subsequently, Cd was back-extracted from the RTIL phase with 500 μL of 0.5 mol L⁻¹ nitric acid and determined by electrothermal atomic absorption spectrometry (ETAAS). A preconcentration factor of 40 was achieved with 20 mL of sample. The limit of detection (LOD) obtained under optimum conditions was 3 ng L⁻¹ and the relative standard deviation (R.S.D.) for 10 replicates at 1 μg L⁻¹ Cd²⁺ concentration level was 3.5%, calculated at peak heights. The calibration graph was linear from concentration levels near the detection limits up to at least 5 μg L⁻¹. A correlation coefficient of 0.9997 was achieved. Validation of the methodology was performed by standard addition method and analysis of certified reference material (CRM). The method was successfully applied to the determination of Cd in river and tap water samples.     

Selective determination method for measurement of nitrite and nitrate in water samples using high-performance liquid chromatography with post-column photochemical reaction and chemiluminescence detection

A simple, sensitive and selective method for the simultaneous determination of nitrite and nitrate in water samples has been developed. The method is based on ion-exchange separation, online photochemical reaction, and luminol chemiluminescence detection. The separation of nitrite and nitrate was achieved using an anion-exchange column with a 20 mM borate buffer (pH 10.0). After the separation, these ions were converted to peroxynitrite by online UV irradiation using a low-pressure mercury lamp and then mixed with a luminol solution prepared with carbonate buffer (pH 10.0). The calibration graphs of the nitrite and nitrate were linear in the range from 2.0 × 10⁻⁹ to 2.5 × 10⁻⁶ M and 2.0 × 10⁻⁸ to 2.5 × 10⁻⁵ M, respectively. Since the sensitivity of nitrite was about 10 times higher than that of nitrate, the simultaneous determination of nitrite and nitrate in the water samples could be efficiently achieved. This method was successfully applied to various water samples – river water, pond water, rain water, commercial mineral water, and tap water – with only filtration and dilution steps.     

Analysis of thyroid hormones in raw and treated waste water

An analytical method for the quantification of thyroid hormones (3,5,3′,5′-tetraiodo-l-thyronine, 3,3′,5-triiodo-l-thyronine, 3,3′,5′-triiodothyronine, 3,5-diiodothyronine, 3,3′-diiodothyronine) in different water matrices has been developed. The method, consisting of solid phase extraction (SPE) and liquid chromatography–tandem mass spectrometry (LC–MS/MS), was validated for tap and surface water as well as raw and treated waste water. The limits of quantifications (LOQs) were lowest in tap water, where they ranged from 1.1 to 13.3 ng L⁻¹, and highest in raw wastewater (10.5–84.9 ng L⁻¹). Of the target analytes 3,5,3′,5′-tetraiodo-l-thyronine (T₄) could be quantified in the influent and effluent of a waste water treatment plant (WWTP) in Finland. The study showed that despite a relatively high removal rate during treatment (66%), part of the incoming T₄ will reach the aquatic environment and, due to the high endocrine activity of this compound, further studies are needed in order to assess its environmental fate and impact on natural ecosystems.     

Reactive extractive electrospray ionization tandem mass spectrometry for sensitive detection of tetrabromobisphenol A derivatives

Sensitive detection of tetrabromobisphenol A (TBBPA) and its derivatives, a group of emerging toxic contaminants, is highly necessitated in environmental investigation. Herein a novel analytical strategy based on reactive extractive electrospray ionization (EESI) tandem mass spectrometry for detection of tetrabromobisphenol A bis(2-hydroxyethyl ether) (TBBPA-BHEE), tetrabromobisphenol A bis(glycidyl ether) (TBBPA-BGE), tetrabromobisphenol A bis(allylether) (TBBPA-BAE), and tetrabromobisphenol S bis(allylether) (TBBPS-BAE) in industrial waste water samples was developed. Active silver cations (Ag⁺), generated by electrospraying a silver nitrate methanol solution (10 mg L⁻¹), collides the neutral TBBPA derivatives molecules in the EESI source to form [M + Ag]⁺ complexes of the analytes under the ambient conditions. Upon collision-induced dissociation (CID), characteristic fragments of the [M + Ag]⁺ complexes were identified for confident and sensitive detection of the four TBBPA derivatives. Under the optimized experimental conditions, the instrumental limits of detection (LODs) of TBBPA-BHEE, TBBPA-BGE, TBBPA-BAE and TBBPS-BAE were 0.37, 0.050, 0.76, and 4.6 μg L⁻¹, respectively. The linear ranges extended to 1000 μg L⁻¹ (R² ≥ 0.9919), and the relative standard deviations (RSDs), inter-day variation and intra-day variation were less than 7.8% (n = 9), 10.0% (n = 5), and 14.8% (n = 1 per day for 5 days) for all derivatives. TBBPA derivative manufacturing industrial waste water, river water and tap water samples were fast analyzed with the proposed method. The contents of TBBPA derivatives were various in the collected samples, with the highest 19.9 ± 0.3 μg L⁻¹ of TBBPA-BAE in the waste water samples.     

Flow injection analysis system based on amperometric thin-film transducers for free chlorine detection in swimming pool waters

This work reports on the performance of a user-friendly flow injection analysis (FIA) system for the monitoring of free chlorine. A methacrylate flow cell integrating a gold thin-film microelectrode, together with an on-chip gold counter electrode, both fabricated by microfabrication technology, provided robustness, low output impedance, rapid response and low cost to the proposed flow system. An external Ag/AgCl reference electrode placed downstream the chip completes the electrochemical cell. Amperometric detection of chlorine was carried out at a set potential of +350 mV, without oxygen interference. The proposed flow system responded linearly to chlorine concentrations in a range from 0.2 to 5 mg l⁻¹, with a sensitivity of 0.23 μA l mg⁻¹, the estimated limit of detection being 0.02 mg l⁻¹. In addition, the system response was kept stable for at least 10 days (±3σ criterion), by keeping the flow system in an inert atmosphere when not in use. Fifteen samples of swimming pool waters were analyzed and no matrix effects were detected. Also, results were in good agreement with those obtained by a standard method. The excellent analytical performance of the system together with its good working stability would also enable its application for the detection of chlorine in other matrices such as tap water or chlorine stock solutions.     

Simultaneous UV and electrochemical determination of the herbicide asulam in tap water samples by micellar electrokinetic capillary chromatography

A simple end-column electrochemical detector was designed and attached to an available commercial capillary electrophoresis instrument with UV detection to detect different kind of herbicides and to determinate methyl-4-aminophenyl-sulfonylcarbamate (asulam) in water samples. The designed cell is very easy to assemble and disassemble in a short period of time; the working electrode positioning is also quickly achieved without micropositioners. The alignment between working electrode and capillary outlet was very reproducible for the all checked electrodes; the R.S.D. obtained was lower than 6.0% for 100 μm gap distance. In this mode, the non-electroactive and electroactive compounds could be detected by UV and electrochemical detection, respectively at the same time. The electrochemical determination of asulam using micellar electrokinetic capillary chromatography (MEKC) is the first time that is reported. In both detection systems, a linear range was obtained for asulam concentrations lower than 25.0 mg l⁻¹, in boric acid 0.020 mol l⁻¹ at pH 8.20 and containing 0.025 mol l⁻¹ of sodium dodecyl sulfate, to obtain selectivity additional separation by the micellar distribution process. Under these conditions, an experimental detection limit of 0.4 mg l⁻¹ was achieved. A new experimental scheme is also described for asulam determination in tap waters with a previous preconcentration step. Using both, UV and electrochemical detection, with a previous extraction procedure, the detection limits of asulam in tap water samples were of 1.0 and 0.8 μg l⁻¹, respectively.