Electrochemical determination of para-nitrophenol at apatite-modified carbon paste electrode: application in river water samples

The behavior of a modified carbon paste electrode (CPE) for para-nitrophenol detection by cyclic and square wave voltammetry (SWV) was studied. The electrode was built by incorporating the hydroxyapatite (HAP) to carbon paste. The overall analysis involved a two-step procedure: an accumulation step at open circuit, followed by medium exchange to a pure electrolyte solution for the voltammetric quantification. During the preconcentration step, para-nitrophenol was adsorbed onto hydroxyapatite surface. The influence of various experimental parameters on the HAP-CPE response was investigated (i.e. pH, carbon paste composition, accumulation time). Under the optimized conditions, the reduction peak shows that the peak height was found to be directly proportional to the para-nitrophenol concentration in the range comprised between 2x10(-7) mol L(-1) and 1x10(-4) mol L(-1). With this, it was possible to determine detection limit (DL), which resulted in 8x10(-9) mol L(-1) for peak 1. The proposed electrode (HAP-CPE) presented good repeatability, evaluated in term of relative standard deviation (R.S.D.=2.87%) for n=7 and was applied for para-nitrophenol determination in water samples. The average recovery for these samples was 86.2%.     

Electrochemical determination of trihalomethanes in water by means of stripping analysis

A protocol has been developed and evaluated for the determination of trihalomethanes (THMs) at the submicromolar concentration level in water. This method is based on a three-step stripping analysis that utilizes a single electrochemical cell and that entails (a) direct electrochemical reduction of a trihalomethane at a silver cathode to form halide ions in an aqueous sample containing tetraethylammonium benzoate, (b) capture of the released halide ions as a silver halide film on the surface of a silver gauze anode, and (c) cathodic reduction and quantitation of the silver halide film by means of differential pulse voltammetry. Using this procedure, we have determined THMs individually; bromoform and chloroform have been successfully quantitated in 30 min and with a detection limit of 3.0 μg L(-1) (12 nM) and 6.0 μg L(-1) (50 nM), respectively. In addition, we have employed our methodology to determine the total trihalomethane (TTHM) content in a prepared water sample at a level commensurate with the maximum allowable annual average of 80 μg L(-1) mandated by the United States Environmental Protection Agency. We have compared our TTHM results to those obtained by an independent testing laboratory.     

催化电位法测定环境水样中痕量亚硝酸根的研究

研究了以亚硝酸根对溴酸钾氧化碘化钾的催化作用,用碘离子选择电极跟踪测定催化体系的电位。实验表明,在适宜的条件下,该指示反应为拟一级反应;电位差与亚硝酸讯浓度在测定条件下呈线性关系,其检出限为3.0×10~(-5)mg/mL。该法用于环境水样的测定,其结果良好。     

Electrochemical determination of water in environmental hydraulic fluids using the karl Fischer reaction

Different procedures based on the Karl Fischer reaction were investigated with respect to their applicability for water determinations in environmental hydraulic fluids: (i) continuous coulometry using a recently described diaphragm-free cell; (ii) on-line stripping of water at elevated temperature using either continuous coulometry or direct potentiometry for detection of the liberated water. Except for one of the oils, Statoil PA, which is a poly(α-olefin) with certain polymers added, no significant difference was found among coulometry using an optimized imidazole-buffered methanolic reagent containing 75% (v/v) chloroform, the two different stripping techniques (working in the temperature interval 100-110 °C), and the commercially available Hydranal Coulomat AG-H. The high stability and sensitivity of the coulometric technique described made it possible to work with sample amounts in the low milligram-range, and this is shown to increase the reliability of the coulometric method as compared to normally used procedures.     

Multiclass determination of sunscreen chemicals in water samples by liquid chromatography-tandem mass spectrometry

A novel analytical method based on solid-phase extraction (SPE) and liquid chromatography-electrospray ionization-tandem mass spectrometry (LC-ESI-MS/MS) for the determination of UV sunscreen agents in the water environment is presented. After a thorough investigation of SPE and LC-MS/MS conditions, it permits the enrichment and determination of nine of these compounds in a single methodology, including three very polar sulfonates (e.g., 2-phenylbenzimidazole-5-sulfonic acid, PBSA) and six other less polar compounds (e.g., benzophenone-3, BP-3; octocrylene, OC,...). Other important matters of concern in the determination of UV filters at trace levels in water, i.e., adsorption on glassware and blank contamination problems, have also been discussed and minimized. This methodology affords detection limits between 7 and 46 ng L-1 and SPE recoveries in the range 63-102% from different real water matrixes, except for butylmethoxydibenzoylmethane (BM-DBM), which was not determinable in wastewater samples due to adsorption problems. The application of the method allowed reporting the levels of benzophenone-4 (BP-4) in environmental water samples for the first time, where it was identified as one of the most important in concentration among the UV filters studied, particularly in wastewater (237-1481 ng L-1).     

Development of surfactant assisted spectrophotometric method for determination of selenium in waste water samples

A new, simple and highly selective method for spectrophotometric determination of selenium in waste water samples is described. Selenium(IV) oxidizes I(-) ions into I(2) which subsequently reacts with excess of I(-) ion in the acidic media to give tri-iodide ions (I(3)(-)), and it further reacts with cetylpyridinium cation (CP(+)) to give a violet colored species. The value of molar absorptivity of the ion-associate species in terms of selenium is 1.80 x 10(4) L mol(-1)cm(-1) at lambda(max) 510 nm. The detection limit of the method is 10 ng mL(-1) Se. The calibration curve is linear over 50-1000 ng mL(-1) Se with slope, intercept and co-relation coefficient of 0.23, -4.0 x 10(-4) and +0.99, respectively. None of the tested diverse ions interfered in the present method. The method has been tested for the determination of selenium in waste water samples.     

Use of solid-phase microextraction for the quantitative determination of herbicides in soil and water samples

An in-depth study of SPME optimization and application has been made, considering not only aqueous (surface water and groundwater samples) but also the more complex soil samples. Seven herbicides widely used in the area of study have been selected including five triazine herbicides (atrazine, simazine, terbumeton, terbuthylazine, terbutryn), molinate, and bromacil. linearity range was between 0.1 and 10 ng/mL and the repeatability below 10% when applying the optimized SPME procedure to water samples. Reproducibility was found to be lower than 20% at the 1 ng/mL level, and the limits of determination in environmental water samples using GC/MS (SIM mode) were well below 0.1 ng/mL (values ranging from 10 to 60 ng/L). Extraction of selected herbicides from soil was carried out by microwave-assisted solvent extraction using methanol in screw-capped vials, leading to recoveries over 80% in spiked soil samples at the 5-200 ng/g level. SPME application over methanolic soil extracts required a 10-fold dilution with distilled water. The recommended procedure was found to be fully applicable for quantitative determination of selected herbicides in soils containing low organic matter content with coefficients of variation below or around 10% and limits of determination ranging from 1 to 10 ng/g. Both procedures were applied to real-world surface water and soil samples where several pesticides were detected including atrazine, simazine, terbuthylazine, and molinate.     

Solid-phase microextraction and headspace solid-phase microextraction for the determination of polychlorinated biphenyls in water samples

A solid-phase microextraction (SPME) method has been developed for the quantification of polychlorinated biphenyls (PCBs) in water samples. Parameters such as sampling time, volume of water, volume of headspace, temperature, addition of salts, and agitation of the sample were studied. Because the time for reaching equilibrium between phases takes several hours or days, depending on the experimental conditions, it was necessary to work in nonequilibrium conditions to keep the sample analysis to a reasonable time. The possibility of sampling the headspace over the water sample (HSSPME), instead of immersing the fiber into the water (SPME), was also investigated, and despite the low partition of PCB into the headspace, HSSPME offered higher sensitivity than SPME at 100 °C. The adsorption kinetics for SPME at room temperature, SPME at 100 °C, and HSSPME at 100 °C were investigated and compared. The proposed HSSPME method exhibits excellent linearity and sensitivity. The detection limit was in the sub-ng/L level. This method has been applied to a real industrial harbor water and compared with liquid-liquid extraction. Both techniques offered similar results, but HSSPME was much more sensitive and considerably faster, by eliminating all the manual process intensive sample workup, and reduces solvent consumption entirely. The only drawback was that matrix effects were observed, but with the addition of deuterated surrogates to the sample or the use of a standard addition calibration, accurate quantification can be achieved.     

On-site determination of tin in geological and water samples using novel organic reagent with iodide

A new, simple and sensitive method for spectrophotometric determination of tin (IV) with iodide and amide is described. The Sn(IV)-I(-) complex is extracted with chloroform solution of amide (N-phenylacetamide, N-alkylacetamide, alkyl=butyl, phenyl, hexyl and octyl group) in the strong sulphuric acid solution. Among five amides studied, N-octylacetamide (OAA) has been selected as it yielded best sensitivity. The apparent (at twofold preconcentration) molar absorptivity with respect to tin is (2.40)x10(5)Lmol(-1)cm(-1) at lambda(max), 410nm. The detection limit of the method is 4microgL(-1) Sn. The method is free from interferences of common ions that are normally associated with Sn. The method is highly sensitive and found to be applicable for the rapid determination of tin in water samples at micro-gram levels.     

Modified carbon paste electrode for potentiometric determination of diquat dibromide pesticide in water and urine samples

A carbon paste electrode for diquat dibromide (Dq.2Br) was prepared and fully characterized in terms of composition, usable pH range, response time and temperature. The electrode was applied to the potentiometric determination of diquat ions in water and urine samples with average recoveries of 97.5-104.0% and relative standard deviations of 0.30-4.73%. The electrode is based on the ion pair, namely, diquat-phosphotungstate dissolved in 2-nitrophenyloctyl ether (2-NPOE) as pasting liquid with 1.0% Na-TPB as an additive. The modified electrode showed a near-Nernstian slope of 30.8 mV over the concentration range of 3.8 × 10^− 6to 1.0 × 10^− 3 M with the limit of detection 9.0 × 10^− 7 over the pH range 4.5-9.5. The electrode exhibits good selectivity for Dq cations with respect to a large number of inorganic cations, organic cations, sugars and amino acids. The proposed potentiometric method offers the advantages of simplicity, accuracy, automation feasibility and applicability to turbid and colored sample solutions.     

Biosensor-based determination of riboflavin in milk samples

An assay for quantification of riboflavin (Rf) in milk-based products has been developed using the principle of surface plasmon resonance with on-chip measurement. The quantification was done indirectly by measuring excess of Rf binding protein (RBP) that remains free after complexation with Rf molecules originally present in the sample solution. The chip was modified with covalently immobilized Rf in order to bind the RBP in excess. A chemical modification was performed to introduce a reactive ester group at the N-3 position of the natural Rf to bind amino groups present on the chip surface. Calibration solutions were prepared by mixing a range of Rf standard solutions with an optimized concentration of RBP. The Rf content in the milk-based products was then measured by comparison of the response against the calibration. Results obtained were very close to those from an official HPLC-fluorescence procedure. The limit of quantification was determined to 234 microg/L and the limit of detection to 70 microg/L by an injection volume of 160 microL.     

超声辅助-乳化液液微萃取-气相色谱法测定水体中7种苯系物

采用正己烷为萃取剂,乙腈为乳化剂,建立超声辅助-乳化液液微萃取-气相色谱法(USA-ELLME-GC)检测水中甲苯、乙苯、对二甲苯、间二甲苯、邻二甲苯、1,3,5-三甲苯,1,2,4-三甲苯的分析方法。当萃取剂正己烷为150μL,乳化剂乙腈为400μL,超声时间为12 min时,50 m L水溶液中苯系物被成功萃取到正己烷中,富集倍数达到333倍。色谱条件为:DB-5MS(30 m×0.25 mm,0.25μm)毛细管柱,进样口温度220℃,检测器(FID)温度250℃,程序升温(初始45℃保持3 min,3°C/min升温至70℃,再以30℃/min升至200℃保持2 min),氢气流量10m L/min,尾吹气流量30 m L/min,分流比30∶1。在优化的萃取和色谱条件下,7种苯系物在0.08~1.00 mg/L浓度范围内与峰面积呈线性关系,相关系数均0.9980,方法检出限为0.005~0.01 mg/L,质量浓度均为0.10 mg/L的苯系物的7次前处理及测定结果相对标准偏差RSD为1.5%~4.7%。建立的方法应用于学校内湖水和实验室废水中7种苯系物的测定,平均回收率为86.5%~110.4%,测定结果满足分析化学痕量分析要求。     

Heptadentate Schiff-base based PVC membrane sensor for Fe(III) ion determination in water samples

Tests performed using heptadentate Schiff's base ((tris(3-(thiophenal)propyl)amine (TTA)) toward Fe(III) ions indicated that it could be used as an Fe(III) selective ionophore to be used in a plasticized polymeric membrane sensor. The resulting sensors were found to produce a linear response range of five orders of magnitude with a slope of 19.8 ± 0.3 mV decade^− 1 with a detection limit is 8.3 × 10^− 9 mol L^− 1. The sensor could be used in a pH window of 2.4-4.3 and the response time of the sensor was below 10 s, in addition to its very good Fe(III) selectivity over many mono-,di- and trivalent transition and heavy metal ions. The life time of the electrode was found to be at least 10 weeks.     

Indirect inductively coupled plasma atomic emission determination of fluoride in water samples by flow injection solvent extraction

An indirect determination of fluoride in water by inductively coupled plasma atomic emission spectrometry combined with flow injection coupled with solvent extraction is reported in this paper. A manifold for rapid determination of fluoride has been designed that uses a single coil for complex formation and extraction. The method involves the formation of lanthanum/alizarin complexone/fluoride complex and its extraction into hexanol containing N,N-diethylaniline. The concentration of fluoride is determined indirectly by introduction of the organic layer into the plasma and measurement of the emission intensity of the La II 333.75-nm line. The optimum experimental conditions for the determination are described. A coiled groove phase separator fitted with a grid and PTFE porous membrane was used in this work. The sampling rate was 36 samples per hour and the calibration graphs were linear from 0.03 to 1.3 micrograms/mL. The relative standard deviation found was 2.16% for 200 microL of 1 microgram/mL of fluoride. The method is selective and has been applied satisfactorily to the determination of fluoride in water samples.     

Spectrophotometric determination of mercury in water samples after cloud point extraction using nonionic surfactant Triton X-114

A cloud point extraction process using the nonionic surfactant Triton X-114 for extracting mercury from aqueous solutions was investigated. The method is based on the complexation reaction of Hg(II) with Thio-Michler's Ketone (TMK) and micelle-mediated extraction of the complex. The optimal extraction and reaction conditions (e.g., pH, reagent concentration, effect of time) were studied, and the analytical characteristics of the method (e.g., limit of detection, linear range) were obtained. Linearity was obeyed in the range of 5.0-80.0 ng mL(-1) of Hg(II) ion. The detection limit of the method was 0.83 ng mL(-1) of Hg(II) ion. The interference effect of some anions and cations was also tested. The method was applied to the determination of mercury in water samples.     

Rapid determination of 226Ra in urine samples

A new radiochemical separation method has been developed for rapid analysis of (226)Ra in urine samples. In this method, radium is separated from urine matrix using cation and anion exchange column chromatography. A (224)Ra tracer is added, together with its parent in the (228)Th standard, for chemical recovery correction. After separation, the sample is precipitated with hydrous titanium oxide and then prepared for counting by creating a thin-layer counting source using BaSO(4) micro-precipitation. The radium isotopes are then counted by alpha spectrometry. Replicate spike and blank samples were analysed for validation of the procedure. The detection limit was determined to be 0.22 Bq l(-1) with 4 h of counting for 20 ml of urine sample. Using this method, the results can be reported within an 8 h turn-around time. This method is suitable for quick dose assessment of (226)Ra exposure following a radiation emergency.     

Cloud-point preconcentration and spectrophotometric determination of trace amounts of molybdenum(VI) in steels and water samples

A cloud-point extraction process using micelle of the cationic surfactant CTAB to extract Mo(VI) from aqueous solutions was investigated. The method is based on the color reaction of molybdenum with bromopyrogallol red in the presence of potassium iodide at pH 1.0 glycine/HCl buffer media and micelle-mediated extraction of complex. The optimal extraction and reaction conditions (e.g., surfactant concentration, reagent concentration and effect of time) were studied and the analytical characteristics of the method (e.g., limit of detection, linear range, preconcentration and improvement factors) were obtained. Linearity was obeyed in the range of 0.3-320.0 ng mL(-1) of molybdenum(VI) ion and the detection limit of the method was 0.1 ng mL(-1). The relative standard deviation (R.S.D.) and relative error for five replicate measurements of 65.0 ng mL(-1) Mo(VI) were 1.1% and 1.9%, respectively. The interference effect of some anions and cations was also tested. The method was applied to the determination of molybdenum(VI) in steels and tap water and well water samples.