Determination of chlorinated by-products of parabens in swimming pool water

We describe the determination of trace amounts of chlorinated parabens, i.e. disinfection by-products, in swimming pool water, using gas chromatography-mass spectrometry with selected ion monitoring (GC-MS-SIM). A dichlorinated by-product of isopropylparaben was detected at levels of up to 25 ng L^?1. Further, a dichlorinated by-product of methylparaben and a monochlorinated by-product of benzylparaben were present in concentrations lower than the limit of quantification. Benzylparaben, the parent compound, was also detected at concentrations of up to 28 ng L^?1. Thus, in this study, chlorinated parabens were detected and quantified for the first time as disinfection by-products in swimming pool water. The results of this study have raised concerns regarding the chlorinated by-products of active ingredients used in personal care products.     

Synthetic approaches to parabens molecularly imprinted polymers and their applications to the solid-phase extraction of river water samples

In this paper we describe the synthesis, characterisation and use of two distinct molecularly imprinted polymers (MIPs) prepared using esters of p-hydroxybenzoic acid (parabens) as templates: one MIP was synthesised by precipitation polymerisation using a semi-covalent molecularly imprinting strategy with methyl paraben as the template/target (MIP 1); the second MIP was prepared in monolithic form through a conventional non-covalent molecular imprinting strategy, with butyl paraben as the template (MIP 2). MIP 1 recognized methyl paraben, showed cross-selectivity for other parabens analytes used in the study and higher affinity towards these compounds than did a non-imprinted control polymer. Similarly, MIP 2 demonstrated higher affinity towards paraben analytes than a non-imprinted control polymer.For the analysis of environmental water samples, a solid-phase extraction (SPE) protocol was developed using MIP 2 as sorbent, and results were compared to a SPE using a commercial sorbent (Oasis HLB). With MIP 2 as sorbent and butyl paraben as target, when percolating 500 mL of river water spiked at 1 μg L⁻¹ through the SPE cartridge, and using 1 mL of isopropanol as cleaning solvent, a higher recovery of butyl 4-hydroxybenzoate (butyl paraben) and a cleaner chromatogram where achievable when using the MIP compared to the commercial sorbent.     

Gas-diffusion flow injection assay for the selective determination of chlorine dioxide based on the fluorescence quenching of chromotropic acid

The present work reports the first spectrofluorimetric gas-diffusion flow injection (GD-FI) assay for the determination of chlorine dioxide in water samples (tap, mineral and soda water). The method is based on the fluorescence quenching of chromotropic acid (CA) (λ_ex. = 347 nm, λ_em. = 371 nm) caused by the analyte. The chemical and instrumental variables of the system were studied in terms of maximum sensitivity. The gas-diffusion cell was thermostated at 40 °C to enhance the vaporization of chlorine dioxide and thus the sensitivity of the method. The quenching effect of chlorine dioxide on CA was linear in the range 0.09-3.41 mg l^− 1, while the precisions either close to the quantitation limit or near to the middle of the linear section of the calibration graph were satisfactory in both cases (s_r = 2.6% and 1.5% (n = 10) at 0.17 and 1.71 mg l^− 1 level, respectively). The developed method proved to be adequately selective and sensitive with 3σ limit of detection equal to c_L = 0.03 mg l^− 1. The application of the assay to spiked tap, mineral and soda water samples yielded accurate results with recovery values in the range 94.1-105.9%.     

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.     

Rapid IC-ICP/MS method for simultaneous analysis of iodoacetic acids, bromoacetic acids, bromate, and other related halogenated compounds in water

Haloacetic acids (HAAs) and bromate are toxic water disinfection by-products (DBPs) that the U.S. Environmental Protection Agency has regulated in drinking water. Iodoacetic acids (IAAs) are the emerging DBPs that have been recently found in disinfected drinking waters with higher toxicity than their corresponding chloro- and bromo-acetic acids. This study has developed a new rapid and sensitive method for simultaneous analysis of six brominated and four iodinated acetic acids, bromate, iodate, bromide, and iodide using ion chromatography-inductively coupled plasma-mass spectrometry (IC-ICP-MS). Mono-, di- and tri-chloroacetic acids are not detected by this method because the sensitivity of ICP-MS analysis for chlorine is poor. Following IC separation, an Elan DRC-e ICP-MS was used for detection, with quantitation utilizing m/z of 79, 127, and 74 amu for Br, I, and Ge (optional internal standard) species, respectively. Although the primary method used was an external standard procedure, an internal standard method approach is discussed herein as well. Calibration and validation were done in a variety of natural and disinfection-treated water samples. The method detection limits (MDLs) in natural water ranged from 0.33 to 0.72 μg L⁻¹ for iodine species, and from 1.36 to 3.28 μg L⁻¹ for bromine species. Spiked recoveries were between 67% and 123%, while relative standard deviations ranged from 0.2% to 12.8% for replicate samples. This method was applied to detect the bromine and iodine species in drinking water, groundwater, surface water, and swimming pool water.     

Development of a thermal desorption-gas chromatography–mass spectrometry method for determining personal care products in air

This study describes the development of a new analytical method for determining 14 personal care products (PCPs) – nine synthetic musks, four parabens and one insect repellent – in air samples. The method is based on active sampling on sorbent tubes and thermal desorption-gas chromatography–mass spectrometry analysis, and is rapid, sensitive and drastically reduces the risk of sample contamination. Three kinds of tubes and traps were tested, those filled with Tenax TA being the most suitable for this study. Method validation showed good repeatability and reproducibility, low detection limits (between 0.03 ng m⁻³ for DPMI and 12.5 ng m⁻³ for propyl paraben) and good linearity for all compounds. Stability during storage indicated that samples must be kept refrigerated at 4 °C and analysed within 1 week of collection. The applicability of the technique to real samples was tested in different indoor and outdoor atmospheres. The total PCP values for indoor air ranged from 135 ng m⁻³ in a pharmacy to 2838 ng m⁻³ in a hairdresser's, whereas the values for outdoor air ranged from 14 ng m⁻³ for a suburban environment to 26 ng m⁻³ for an urban environment. In general, the most abundant synthetic musks were galaxolide (5.9–1256 ng m⁻³), musk xylene (1.6–766 ng m⁻³) and tonalide (1.1–138 ng m⁻³). Methyl and ethyl paraben (2.4–313 ng m⁻³ and 1.8–117 ng m⁻³, respectively) were the most abundant parabens. Although thermal desorption methods have been widely used for determining volatile organic compounds, they are rarely used with semi-volatile compounds. This study thus demonstrates that the thermal desorption method performs well with semi-volatile compounds and, for the first time, that it can be used for determining PCPs.     

Aquatic degradation of triclosan and formation of toxic chlorophenols in presence of low concentrations of free chlorine

The degradation of 2-(2,4-dichlorophenoxy)-5-chlorophenol (triclosan) in chlorinated water samples was investigated. Sensitive determination of the parent compound and its transformation products was achieved by gas chromatography with mass spectrometry detection after sample concentration, using a solid-phase extraction sorbent and silylation of the target compounds. Experiments were accomplished using ultrapure water spiked with chlorine and triclosan concentrations in the low mg/l and ng/ml ranges respectively. Chlorination of the phenolic ring and cleavage of the ether bond were identified as the main triclosan degradation pathways. Both processes led to the production of two tetra- and a penta-chlorinated hydroxylated diphenyl ether, as well as 2,4-dichlorophenol. The formation of 2,3,4-trichlorophenol was not detected in any experiment; however, significant amounts of 2,4,6-trichlorophenol were noticed. All of these five compounds were also identified when triclosan was added to tap-water samples with free chlorine concentrations below 1 mg/l. Minor amounts of three di-hydroxylated phenols, containing from one to three atoms of chlorine in their structures, were also identified as unstable triclosan chlorination by-products. The analysis of several raw wastewater samples showed the co-existence of important concentrations of triclosan and its most stable by-products (2,4-dichlorophenol and 2,4,6-trichlorophenol), reinforcing the potential occurrence of the described transformations when products containing triclosan are mixed with chlorinated tap water.     

Determination of parabens in cosmetic products using multi-walled carbon nanotubes as solid phase extraction sorbent and corona-charged aerosol detection system

The potential of carbon nanotubes for the solid phase extraction of parabens in cosmetic products and the detection using a corona-charged aerosol detector (C-CAD) is presented in this work. The analytical procedure is based on a conventional solid phase extraction step for which 20 mg of multi-walled carbon nanotubes were packed in a 3-mL commercial SPE cartridge. Methylparaben, ethylparaben, propylparaben and butylparaben were thus isolated and preconcentrated from the pre-treated samples and subsequently separated on a RP-C18 column using acetonitrile:water, 50:50 (v/v) as mobile phase. The analytical signals for the individual parabens were obtained using C-CAD. The experimental variables affecting the extraction procedure and the instrumental detection have been deeply studied. Limits of detection were in the range of 0.5–2.1 mg L⁻¹, while the linear range was extended up to 400 mg L⁻¹. The average precision of the method varied between 3.3–3.8% (repeatability) and 4.3–7.6% (reproducibility). Finally, the optimized procedure was applied to the determination of the target preservatives in a variety of cosmetic products with satisfactory results.     

Molecularly imprinted polymer for the extraction of parabens from environmental solid samples prior to their determination by high performance liquid chromatography-ultraviolet detection

An analytical methodology incorporating a molecularly imprinted solid-phase extraction procedure (MISPE) has been developed for the determination of parabens in environmental solid samples. Four different polymers were prepared combining the use of acetonitrile or toluene as porogen, and 4-vinylpyridine (VP) or methacrylic acid (MAA) as monomer, using benzylparaben (BzP) as a template molecule. Although all the polymers were able to recognize the template in rebinding experiments, the MIP prepared in toluene using MAA showed better performance. This polymer was also capable of recognizing other parabens (methyl, ethyl, isopropyl, propyl, isobutyl, butyl and benzylparaben) allowing to develop an appropriated MISPE procedure for this family of compounds. The extraction of the parabens from environmental solid samples was performed by ultrasonic assisted extraction in small columns (SAESC), and this procedure next to MISPE as clean-up step followed by HPLC-UV determination was successfully used for the determination of parabens in soil and sediment samples of different locations. Recoveries ranging from 80% to 90% have been achieved depending on the compound and the samples, and limits of detection (LODs) were under 1 ng g⁻¹ for all the compounds, making this method suitable for the determination of parabens in environmental solid matrices. The method was further applied to the determination of paraben contents in real samples, founding levels up to 11.5 ng g⁻¹ in sea sediments.     

Determination of trace bisphenol A in complex samples using selective molecularly imprinted solid-phase extraction coupled with capillary electrophoresis

The highly selective, fast and effective sample pretreatment technique molecularly imprinted solid-phase extraction (MISPE) can overcome the low sensitivity of the highly efficient capillary electrophoresis-UV method (CE-UV). In this work, narrowly dispersible bisphenol A (BPA)-imprinted polymeric microspheres with a high capacity factor of k′ = 6.8 and an imprinted factor of I = 6.53 were investigated as selective solid-phase extraction (SPE) sorbents for use in extraction of BPA from different sample matrices (tap water, wastewater, Yangtze River water, soil from the Yangtze River, shrimp and human urine). Washing and eluting protocols of MISPE were optimized. Under optimal conditions, recoveries of MISPE were investigated. Recoveries were basically constant and the relative standard deviation (RSD) was lower than 5.8% when loading volumes changed from 1 to 50 mL. Recoveries ranged from 71.20% to 86.23% for different sample matrices. Compared with C18 SPE, MISPE had higher selectivity and recovery for BPA. BPA was determined with good accuracy and precision in different complex samples using CE-UV coupled with MISPE. Spiked recoveries ranged from 95.20% to 105.40%, and the RSD was less than 7.2%. Because a large loading volume was achieved, the enrichment efficiency of pretreatment and the sensitivity of this method were improved. The limits of detection of this MISPE-CE-UV method for BPA in tap water, wastewater, Yangtze River water, soil from the Yangtze River, shrimp and human urine were 3.0 μg L^− 1, 5.4 μg L^− 1, 6.9 μg L^− 1, 2.1 μg L^− 1, 1.8 μg L^− 1 and 84 μg L^− 1, respectively.     

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.     

Leachability and analytical speciation of antimony in coal fly ash

A new procedure was described with multiwalled carbon nanotubes as solid phase extraction packing material for the trace analysis of nicosulfuron, thifensulfuron and metsulfuron-methyl in water samples. The possible parameters influencing the enrichment were optimized and the optimal conditions were as followed: eluent, sample pH, flow rate and sample volume were acetonitrile containing 1% acetic acid, pH 3, 8 mL min⁻¹ and 500 mL, respectively. Under the optimal chromatographic separation and SPE conditions, the linear range, detection limit (S/N = 3) and precision (R.S.D., n = 6) were 0.04-40 ng mL⁻¹, 6.8 ng L⁻¹ and 2.5% for nicosulfuron, 0.04-40 ng mL⁻¹, 11.2 ng L⁻¹ and 5.4% for thifensulfuron, 0.02-20 ng mL⁻¹, 5.9 ng L⁻¹, 2.1% for metsulfuron-methyl, respectively. The established method was well employed to determine nicosulfuron, thifensulfuron and metsulfuron-methyl in tap water, seawater, reservoir water and well water samples, and satisfactory results were obtained, the spiked recoveries in the range of 87.2-100.7%, 96.5-105.6% and 83.7-111.1% for them each, respectively.     

Combination of off-line solid-phase extraction and on-column sample stacking for sensitive determination of parabens and p-hydroxybenzoic acid in waters by non-aqueous capillary electrophoresis

For the first time, a procedure based on solid-phase extraction (SPE) for the simultaneous extraction of a group of parabens (methyl, ethyl, propyl, butyl and benzyl p-hydroxybenzoates) and p-hydroxybenzoic acid (PHBA), from environmental water samples has been developed. Analysis of the extracts was performed by non-aqueous capillary electrophoresis (NACE) coupled with diode array detection (DAD), using large-volume sample stacking (LVSS) based on the electroosmotic flow pump as on-column preconcentration technique. Several water samples, such as tap, river, and wastewater samples, were analyzed using both SPE-NACE-DAD and SPE-LVSS-NACE-DAD methods. It has been observed that in addition to SPE parameters such as sorbent material, sample pH, breakthrough volume, addition of an organic solvent and elution solvent, also sample characteristics, such as organic matter content, have influence on SPE extraction yields, especially in the case of PHBA. The presence of PHBA and some parabens was detected at trace levels in surface water samples. Concentrations up to 8.4 ng mL⁻¹ were found in raw wastewater, with the highest levels corresponding to methylparaben, propylparaben, and their main degradation product, PHBA.     

Selective determination of cyanides by gas diffusion-stopped flow-sequential injection analysis and an on-line standard addition approach

A highly selective sequential injection (SI) method for the automated determination of weak-acid-dissociable cyanides is reported. The analytical procedure is based on the on-line reaction of the analyte with ninhydrin in carbonate medium to form a coloured product (λ_max = 510 nm). Cyanides are removed from sample matrix by acidification through a gas-diffusion step incorporated in the SI manifold. The effect of instrumental and chemical variables was studied. By adopting an on-line standard addition protocol, the sensitivity of the proposed method was enhanced drastically, without affecting the determination range. The assay was validated in terms of linearity (up to 200 μg L⁻¹), limit of detection (c_L = 2.5 μg L⁻¹), limit of quantitation (c_Q = 7.5 μg L⁻¹), precision (s_r < 2.5% at 100 μg L⁻¹) and selectivity. High tolerance against critical species such as sulfides and thiocyanates was achieved. The applicability of the method was demonstrated by analyzing tap and mineral water samples at levels below the limits established by international E.U. and U.S. organizations. The percent recoveries were satisfactory in all cases, ranging between 94.2 and 103.6%.     

Headspace liquid-phase microextraction using ionic liquid as extractant for the preconcentration of dichlorodiphenyltrichloroethane and its metabolites at trace levels in water samples

A novel technique, high temperature headspace liquid-phase microextraction (HS-LPME) with room temperature ionic liquid (RTIL), 1-butyl-3-methylimidazolium hexafluorophosphate ([C₄MIM][PF₆]) as extractant, was developed for the analysis of dichlorodiphenyltrichloroethane (p,p′-DDT and o,p′-DDT) and its metabolites including 4,4′-dichlorodiphenyldichloroethylene (p,p′-DDE) and 4,4′-dichlorodiphenyldichloroethane (p,p′-DDD) in water samples by high performance liquid chromatography with ultraviolet detection. The parameters such as salt content, sample pH and temperature, stirring rate, extraction time, microdrop volume, and sample volume, were found to have significant influence on the HS-LPME. The conditions optimized for extraction of target compounds were as follows: 35% NaCl (w/v), neutral pH condition, 70 °C, 800 rpm, 30 min, 10 μL [C₄MIM][PF₆], and 25 mL sample solutions. Under the optimized conditions, the linear range, detection limit (S/N = 3), and precision (R.S.D., n = 6) were 0.3-30 μg L⁻¹, 0.07 μg L⁻¹, and 8.0% for p,p′-DDD, 0.3-30 μg L⁻¹, 0.08 μg L⁻¹, and 7.1% for p,p′-DDT, 0.3-30 μg L⁻¹, 0.08 μg L⁻¹, and 7.2% for o,p′-DDT, and 0.2-30 μg L⁻¹, 0.05 μg L⁻¹, and 6.8% for p,p′-DDE, respectively. Water samples including tap water, well water, snow water, reservoir water, and wastewater were analyzed by the proposed procedure and the recoveries at 5 μg L⁻¹ spiked level were in the range of 86.8-102.6%.     

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.     

An environmentally friendly flow system for high-sensitivity spectrophotometric determination of free chlorine in natural waters

A green and highly sensitive analytical procedure was developed for the determination of free chlorine in natural waters, based on the reaction with N,N-diethyl-p-phenylenediamine (DPD). The flow system was designed with solenoid micro-pumps in order to improve mixing conditions by pulsed flows and to minimize reagent consumption as well as waste generation. A 100-cm optical path flow cell based on a liquid core waveguide was employed to increase sensitivity. A linear response was observed within the range 10.0 to 100.0 µg L^− 1, with the detection limit, coefficient of variation and sampling rate estimated as 6.8 µg L^− 1 (99.7% confidence level), 0.9% (n = 20) and 60 determinations per hour, respectively. The consumption of the most toxic reagent (DPD) was reduced 20,000-fold and 30-fold in comparison to the batch method and flow injection with continuous reagent addition, respectively. The results for natural and tap water samples agreed with those obtained by the reference batch spectrophotometric procedure at the 95% confidence level.     

Flow-injection investigation of the chemiluminescent reaction of bis(2,4,6-(trichlorophenyl)oxalate) with free chlorine

This work investigated the chemiluminescent reaction of free chlorine with bis(2,4,6-(trichlorophenyl)oxalate) (TCPO) in the presence of 9,10-diphenylanthracene in acetonitrile/water medium, with analytical application for free chlorine in tap water. In the absence of free chlorine, the background signal increased with the pH and the chemiluminescence emission showed strong dependence with the sample acidity. A flow injection analysis system, for free chlorine determination, was developed. The linear range for free chlorine was (0.2-3.0)×10⁻⁵ mol l⁻¹. Chloramine 1.0×10⁻⁵ mol l⁻¹ and chlorite 1.0×10⁻⁶ mol l⁻¹ also enhanced the chemiluminescence intensity.     

Development of a flow system for the determination of low concentrations of silver using Moringa oleifera seeds as biosorbent and flame atomic absorption spectrometry

In this study a method for the determination of low concentrations of silver in waters using solid-phase extraction with a flow injection analysis system and detection by flame atomic absorption spectrometry (FAAS) was developed. Moringa oleifera seeds were used as a biosorbent material. Chemical and flow variables of the on-line preconcentration system such as sample pH and flow rate, preconcentration time, eluent concentration and sorbent mass were studied. The optimum preconcentration conditions were obtained using sample pH in the range of 6.0-8.0, preconcentration time of 4 min at a flow rate of 3.5 mL min^− 1, 0.5 mol L^− 1 HNO₃ eluent at a flow rate of 4.5 mL min^− 1 and 35 mg of sorbent mass. With the optimized conditions, the preconcentration factor, precision, detection limit and sample throughput were estimated as 35 (for preconcentration of 14 mL sample), 3.8% (5.0 μg L^− 1, n = 7), 0.22 μg L^− 1 and 12 samples per hour, respectively. The developed method was successfully applied to mineral water and tap water, and accuracy was assessed through analysis of a certified reference material for water (APS-1071 NIST) and recovery tests, with recovery ranging from 94 to 101%.     

Langmuir-Blodgett film of p-tert-butylthiacalix[4]arene modified glassy carbon electrode as voltammetric sensor for the determination of Hg(II)

The π-A isotherms and UV-vis spectra of the transferred films suggested that the monolayer of p-tert-butylthiacalix[4]arene can coordinate with Hg²⁺ at the air-water surface. From these observations, a glassy carbon electrode coated with Langmuir-Blodgett film of p-tert-butylthiacalix[4] arene as a new voltammetric sensor is designed for the determination of trace amounts of Hg²⁺. Compared with bare glassy carbon electrode and modified glassy carbon electrode using direct coating method, the Langmuir-Blodgett film-modified electrode can greatly improve the measuring sensitivity of Hg²⁺. Under the selected conditions, the Langmuir-Blodgett film-modified electrode in 0.1 mol L⁻¹ H₂SO₄ + 0.01 mol L⁻¹ KCl solution shows a linear voltammetric response for Hg²⁺ in the range of 5.0 × 10⁻¹⁰ to 1.5 × 10⁻⁷ mol L⁻¹, with a detection limit of 2.0 × 10⁻¹⁰ mol L⁻¹. The proposed method was also applied to determine Hg²⁺ in water samples (tap, lake and river water). In addition, the fabricated electrode exhibited a distinct advantage of simple preparation, non-toxicity, good reproducibility and good stability.