Mercury(II) ion-selective electrodes based on heterocyclic systems

Mercury ion-selective electrodes (ISEs) were prepared with a polymeric membrane based on heterocyclic systems: 2-methylsulfanyl-4-(4-nitro-phenyl)-l-p-tolyl-1H-imidazole (I) and 2,4-diphenyl-l-p-tolyl-1H-imidazole (II) as the ionophores. Several ISEs were conditioned and tested for the selection of common ions. The electrodes based on these ionophores showed a good potentiometric response for Hg2+ ions over a wide concentration range of 5.0 x 10(5-) - 1.0 x 10(-1)M with near-Nernstian slopes. Stable potentiometric signals were obtained within a short time period of 20 s. The detection limits, the working pH range of the electrodes were 1.0 x 10(-5) M and 1.6-4.4 respectively. The electrodes showed better selectivity for Hg2+ ions over many of the alkali, alkaline-earth and heavy metal ions. Also sharp end points were obtained when these sensors were used as indicator electrodes for the potentiometric titration of Hg2+ ions with iodide ions.     

Novel potentiometric membrane sensor for the determination of trace amounts of chromium(III) ions.

A plasticized Cr3+ ion sensor by incorporating 2,3,8,9-tetraphenyl-1,4,7,10-tetraazacyclododeca-1,3,7,9-tetraene (TTCT) ionophore exhibits a good potentiometric response for Cr3+ over a wide concentration range (1.0 x 10(-6)-1.0 x 10(-1) M) with a slope of 19.5 mV per decade. The sensor response is stable for at least three months. Good selectivity for Cr3+ in comparison with alkali, alkaline earth, transition and heavy metal ions, and minimal interference are caused by Li+, Na+, K+, Co2+, Hg2+, Ca2+, Pb2+ and Zn2+ ions, which are known to interfere with other chromium membrane sensors. The TTCT-based electrode shows a fast response time (15 s), and can be used in aqueous solutions of pH 3-5.5. The proposed sensor was used for the potentiometric titration of Cr3+ with EDTA and for a direct potentiometric determination of Cr3+ content in environmental samples.     

Silver(I) ion selective PVC membrane based on bis-pyridine tetramide macrocycle

A PVC membrane based on bis-pyridine tetramide macrocycle exhibits a good response for silver ion over a wide concentration range (1.0x10(-1)-4.0x10(-5) mol l(-1)). The electrode has a relatively fast response time and can be used for more than 5 months without observing any divergence. High selectivity for Ag(+) ions over that of Na(+), K(+), Ca(2+), Sr(2+), Pb(2+) and Hg(2+) have been observed.     

钳状杯[4]芳烃为探针的固态PVC膜汞离子选择性电极

全固膜选择性电极(All solid-state selective electrode,ASSE)综合晶体电极和膜电极的优点,具有线性范围宽、检测限低,能真实地体现膜性能等特点,ASSE主要有涂线电极(Coated wire electrode,CWE)、填充固体电解质或配合物的膜电极和电沉积型聚合物膜电极等。     

Novel mercury (II) ion-selective polymeric membrane sensor based on ethyl-2-benzoyl-2-phenylcarbamoyl acetate

Mercury (II) ion-selective PVC membrane sensor based on ethyl-2-benzoyl-2-phenylcarbamoyl acetate (EBPCA) as a novel nitrogen containing sensing material is successfully developed. The sensor exhibits good linear response of 30 mV per decade within the concentration range 10(-6)-10(-3) mol l(-1) Hg(II). The sensor shows good selectivity for mercury (II) ion in comparison with alkali, alkaline earth, transition and heavy metal ions. The EBPCA-based sensor is suitable for use with aqueous solutions of pH 2.0-4.5 and exhibits minimal interference by Ag(I) and Fe(III), which are known to interfere with other previously suggested sensors. The nature and composition of the sensing material and its mercury complex are examined using Fourier-transform infrared analysis, elemental analysis and X-ray fluorescence techniques. The proposed sensor is applied as a sensor for the determination of Hg(II) content in some amalgam alloys. The results show good correlation with data obtained by atomic absorption spectrometric method.     

New highly selective picrate sensors based on charge-transfer complexes.

Two novel highly selective potentiometric membrane sensors responsive to picrate ion were developed. They are based on the use of N,N'-dibenzoyl-1,4,10,13-tetraoxa-7,16-diazacyclooctadecane (DD18C6)-picrate and Kryptofix 222-picrate charge-transfer complexes as novel electroactive materials in poly(vinyl chloride) matrix membranes plasticized with o-nitrophenyloctylether or dioctylphthalate. The sensors show a Nernstian response with anionic slopes of -59.0 +/- 0.1 and -58.0 +/- 0.2 mV decade(-1) over concentration ranges of 6.0 x 10(-5) - 1.0 x 10(-2) and 7.0 x 10(-5) - 1.0 x 10(-2) mol l(-1) picrate ion and pH ranges of 5-11.5 and 5.5-11.5 for DD18C6 and Kryptofix 222 based picrate sensors, respectively. Both sensors show highly selectivity towards picrate ion over many hydrophilic and lipophilic anions, and exhibit a non-Hofmeister selectivity sequence, which is an improvement over methods reported so far. The sensors are used for the titrimetric determination of alkaloids using picrate as a titrant.     

Flotation-spectrophotometric determination of mercury in water samples using iodide and ferroin.

This paper describes a simple and highly selective method for separation, preconcentration and spectrophotometric determination of trace amounts of mercury. The method is based on the flotation of an ion-associate of HgI4(2-) and ferroin between aqueous and n-heptane interface at pH 5. The ion-associate was then separated and dissolved in acetonitrile to measure its absorbance. Quantitative flotation of the ion-associate was achieved when the volume of the water sample containing Hg(II) was varied over 50 - 800 ml. Beer's law was obeyed over the concentration range of 3.2 x 10(-8) - 9.5 x 10(-7) mol l(-1) with an apparent molar absorptivity of 1 x 10(6) l mol(-1) cm(-1) for a 500 ml aliquot of the water sample. The detection limit (n = 25) was 6.2 x 10(-9) mol l(-1), and the RSD (n = 5) for 3.19 x 10(-7) mol l(-1) of Hg(II) was 1.9%. A notable advantage of the method is that the determination of Hg(II) is free from the interference of the almost all cations and anions found in the environmental and waste water samples. The determination of Hg(II) in tap, synthetic waste, and seawater samples was carried out by the present method and a well-established method of extraction with dithizone. The results were satisfactorily comparable so that the applicability of the proposed method was confirmed in encountering with real samples.     

聚对氨基苯磺酸/石墨烯修饰玻碳电极伏安法测定痕量汞

制备了对氨基苯磺酸/石墨烯复合膜修饰电极,研究了汞在修饰电极上的电化学行为。 在0.1 mol/L、pH=4.0的磷酸盐缓冲液中,以此修饰电极为工作电极,在-1.2 V搅拌富集5 min,用差分脉冲伏安法测定0.31 V处的溶出峰电流。 结果表明,该电极显著提高了汞离子的电化学响应信号。 在优化条件下,峰电流与Hg2+的浓度在1.0×10-6~5.0×10-4 mol/L范围内呈良好的线性关系,相关系数为0.995。 方法的检出限为5.0×10-7 mol/L。 将该法用于水样中痕量汞的测定,回收率为92.2%~105.2%。     

Flow injection amperometric detection of ascorbic acid using a Prussian Blue film-modified electrode

The PB film-modified electrode was used as an amperometric detector for flow injection analysis of ascorbic acid. The modified electrode detector showed good sensitivity, stability and reproducibility. The calibration curve for ascorbic acid was linear over the concentration range from 5.0x10(-6) to 1.0x10(-3) mol l(-1) with a slope of 19.9 mA mol(-1) per litre and a correlation coefficient of 0.999. The detection limit of this method was 2.49x10(-6) mol l(-1). The relative standard deviation of six replicate injections of 2.5x10(-4) mol l(-1) ascorbic acid was 2.5%. The results obtained for ascorbic acid determination in pharmaceutical products are in good agreement with those obtained by using the procedure involving the reaction between triiodide and ascorbic acid.     

Mercury(II) ion-selective electrodes based on p-tert-butyl calix[4]crowns with imine units.

A PVC membrane incorporating p-tert-butyl calix[4]crown with imine units as an ionophore was prepared and used in an ion-selective electrode for the determination of mercury(II) ions. An electrode based on this ionophore showed a good potentiometric response for mercury(II) ions over a wide concentration range of 5.0 x 10(-5) - 1.0 x 10(-1) M with a near-Nernstian slope of 27.3 mV per decade. The detection limit of the electrode was 2.24 x 10(-5) M and the electrode worked well in the pH range of 1.3 - 4.0. The electrode showed a short response time of less than 20 s. The electrode also showed better selectivity for mercury(II) ions over many of the alkali (Na+, -1.69; K+, -1.54), alkaline-earth (Ca2+, -3.30; Ba2+, -3.32), and heavy metal ions (Co2+, -3.67; Ni2+, -3.43; Pb2+, -3.31; Fe3+, -1.82). Ag+ ion was found to be the strongest interfering ion. Also, sharp end points were obtained when the sensor was used as an indicator electrode for the potentiometric titration of mercury(II) ions with iodide and dichromate ions.     

TpPa-1/Nafion修饰电极的差分脉冲阳极溶出伏安法同时测定铜离子和汞离子

通过机械化学合成法合成了一种共价有机框架材料TpPa-1,以此作为电极材料制备化学修饰电极,研究了修饰电极的差分脉冲阳极溶出伏安法(DPASV)同时测定铜离子和汞离子。结果表明,TpPa-1/Nafion修饰电极在磷酸盐缓冲溶液中可实现对Cu^2+和Hg^2+的同时检测。Cu^2+的检出限为5.0×10^-8 mol/L线性范围为1.0×10^-7~5.0×10^-5 mol/L,R^2=0.9975。Hg^2+的检出限为1.0×10^-8 mol/L,线性范围为2.0×10^-8~1.0×10^-4 mol/L,R^2=0.9988。采用上述方法对实际样品进行检测,回收率为97.6%~105.5%,RSD均小于4.0%。     

1-(4-nitrophenyl)-3-(2-quinolyl) triazene as an extremely sensitive reagent for spectrophotometric determination of mercury

1-(4-Nitrophenyl)-3-(2-quinolyl)triazene has been synthesized, and used as an extremely sensitive reagent for the spectrophotometric determination of mercury by the decrease in the absorbance of the reagent at 490 nm and pH 9.0-10.8 in the presence of cetylpyridinium bromide. Beer's law is obeyed over the range 0-120 ng/ml Hg(II), the apparent molar absorptivity being 1.0 x 10(6) l.mole(-1).cm(-1). The effect of 69 ionic species or compounds has been examined. Trace mercury in waste water has been determined satisfactorily.     

Determination of the herbicide desmetryne in organised media by adsorptive stripping voltammetry

An electroanalytical method for the determination of the herbicide desmetryne at nanomolar levels in dispersed media, based on adsorptive stripping voltammetry, is reported. The adsorption of desmetryne at the hanging mercury drop electrode was checked both in micellar solutions, where the anionic surfactant sodium pentanesulphonate was chosen as the most suitable surfactant agent, and in oil-in-water emulsions prepared with ethyl acetate as the organic solvent. In a micellar medium formed with 0.02% sodium pentanesulphonate and with 0.1 mol l(-1) Britton-Robinson buffer (pH 1.5), the herbicide could be determined over the 1.0 x 10(-8)-4.0 x 10(-7) mol l(-1) concentration range, when an accumulation potential of -0.70 V was applied for 50 s. On the other hand, in an oil-in-water emulsion formed with 2% ethyl acetate and 0.04% sodium pentanesulphonate as emulsifying agent in 0.1 mol l(-1) HClO(4), desmetryne could be determined over the 2.0 x 10(-9)-1.0 x 10(-7) mol l(-1) concentration range. The limits of detection were 2.4 x 10(-9) and 4.2 x 10(-10) mol l(-1) in micellar and emulsified media, respectively, with R.S.D.s (n=10) 3.6 and 3.7%. The degree of interference from some other s-triazines on the desmetryne differential pulse response was also evaluated. Finally, the method developed in emulsified medium was applied to the determination of desmetryne in spiked apple juice.     

基于硫氮杂冠醚离子载体的高选择性聚合物膜汞离子选择性电极

以硫氮杂冠醚化合物为离子载体,制备了一种高选择性聚合物膜汞离子选择性电极.通过对电极膜的组成及活化条件进行优化,电极在3.0×10-8～1.0×10-4 mol/L的范围内对汞离子呈能斯特响应,响应斜率为31.2 mV/dec,检出限为2.0×10-8 mol/L.该电极对大多数常见的金属离子具有良好的选择性,并可作为指示电极用于电位滴定.     

Evaluation of a carbon paste electrode modified with organofunctionalised SBA-15 nanostructured silica in the simultaneous determination of divalent lead, copper and mercury ions

The performance of a carbon paste electrode (CPE) modified with SBA-15 nanostructured silica organofunctionalised with 2-benzothiazolethiol in the simultaneous determination of Pb(II), Cu(II) and Hg(II) ions in natural water and sugar cane spirit (cacha?a) is described. Pb(II), Cu(II) and Hg(II) were pre-concentrated on the surface of the modified electrode by complexing with 2-benzothiazolethiol and reduced at a negative potential (-0.80 V). Then the reduced products were oxidised by DPASV procedure. The fact that three stripping peaks appeared on the voltammograms at the potentials of -0.48 V (Pb2+), -0.03 V (Cu2+) and +0.36 V (Hg2+) in relation to the SCE, demonstrates the possibility of simultaneous determination of Pb2+, Cu2+ and Hg2+. The best results were obtained under the following optimised conditions: 100 mV pulse amplitude, 3 min accumulation time, 25 mV s(-1) scan rate in phosphate solution pH 3.0. Using such parameters, calibration graphs were linear in the concentration ranges of 3.00-70.0 x 10(-7) mol L(-1) (Pb2+), 8.00-100.0 x 10(-7) mol L(-1) (Cu2+) and 2.00-10.0 x 10(-6) mol L(-1) (Hg2+). Detection limits of 4.0 x 10(-8) mol L(-1) (Pb2+), 2.0 x 10(-7) mol L(-1) (Cu2+) and 4.0 x 10(-7) mol L(-1) (Hg2+) were obtained at the signal noise ratio (SNR) of 3. The results indicate that this electrode is sensitive and effective for simultaneous determination of Pb2+, Cu2+ and Hg2+ in the analysed samples.     

Optimization of polymeric triiodide membrane electrode based on clozapine-triiodide ion-pair using experimental design

Central composite design (CCD) and response surface methodology (RSM) were developed as experimental strategies for modeling and optimization of the influence of some variables on the performance of a new PVC membrane triiodide ion-selective electrode. This triiodide sensor is based on triiodide-clozapine ion-pair complexation. PVC, plasticizers, ion-pair amounts and pH were investigated as four variables to build a model to achieve the best Nernstian slope (59.9 mV) as response. The electrode is prepared by incorporating the ion-exchanger in PVC matrix plasticized with 2-nitrophenyl octal ether, which is directly coated on the surface of a graphite electrode. The influence of foreign ions on the electrode performance was also investigated. The optimized membranes demonstrate Nernstian response for triiodide ions over a wide linear range from 5.0 x 10(-6) to 1.0 x 10(-2)mol L(-1) with a limit of detection 2.0 x 10(-6) mol L(-1) at 25 degrees C. The electrodes could be used over a wide pH range 4-8, and have the advantages of easy to prepare, good selectivity and fast response time, long lifetime (over 3 months) and small interferences from hydrogen ion. The proposed electrode was successfully used as indicator electrode in potentiometric titration of triiodide ions and ascorbic acid.     

Electrochemical determination of 6-mercaptopurine at silver microdisk electrodes

The electrochemical behaviour of 6-mercaptopurine (6-MP) at a microdisk electrode is investigated by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The results indicate that 6-MP can be strongly adsorbed on the surface of the static mercury drop electrode (SMDE) and reacts with Ag+ ions which are produced at positive potentials. 6-MP yields a well-defined cathodic stripping signal during the negative scan at about -0.812 V (vs. SCE) in pH 9.0 phosphate buffer solution. The electrode has hence been used for the determination of 6-MP by differential pulse voltammetry (DPV). The linear range is between 2.0x10(-7) and 5.0x10(-5) mol/l, with the calculated detection limit (S/N=3) of 8.0x10(-8) mol/l. The relative standard deviation is 3.0% for eight successive determinations of 4.0x10(-5) mol/l 6-MP. The determination of 6-MP in tablets has also been carried out and satisfactory results have been obtained.     

Determination of environmentally important metal ions by fluorescence quenching in anionic micellar solution

This work describes the effect of a variety of metal ions as quenchers of the fluorescence of naphthalene, in aqueous micellar solutions of sodium dodecyl sulfate (SDS). The quenching by the metal ions can be adequately described by the Stern-Volmer equation and the best signal to noise ratios are obtained with low micellized detergent concentrations. Apparent Stern-Volmer constants decrease in the order: Fe3+ > Cu2+ > Pb2+ > Cr3+ > Ni2+ and directly reflect the relative sensitivity of the method for these ions. Detection limits (defined as three times the standard deviation of the blank for n= 10) for the fluorescence quenching of naphthalene by the metal ions in aqueous micellar SDS are in the range of 1.0 x 10(-6) to 1.0 x 10(-5) mol dm(-3). The proposed fluorescence quenching method shows good repeatibility for a variety of added quencher metal ions, indicating that anionic micelle-enhanced fluorescence quenching by metal ions constitutes an analytical method of rather general application.     

Copper(II)-selective electrode using 2,2'-dithiodianiline as neutral carrier

Poly(vinyl chloride) membrane electrode, that is highly selective and sensitive to Cu(II) ions, was developed by using 2,2'-dithiodianiline and dibutyl phthalate as carrier and plasticizer, respectively. The electrode exhibits good potentiometric response for Cu(II) over a wide concentration range (5.0x10(-2)-7.0x10(-7) mol l(-1)) with Nernstian slope of 30+/-1 mV per decade. The response time of the electrode is 10 s and it has been used for a period of one month and exhibits good selectivity towards Cu(2+) in comparison to alkali, alkaline earth, transition and heavy metal ions, with no interference caused by Pb(2+), Cd(2+) and Fe(+2) which are known to interfere with many other copper electrodes.     

A 9,10-anthraquinone derivative having two propenyl arms as a neutral ionophore for highly selective and sensitive membrane sensors for copper(II) ion.

New polymeric membrane (PME) and coated graphite (CGE) copper(II)-selective electrodes based on 1-hydroxy-2-(prop-2'-enyl)-4-(prop-2'-enyloxy)-9,10-anthraquinone were prepared. The electrodes reveal linear emf-pCu2+ responses over wide concentration ranges (1.0 x 10(-5)-1.0 x 10(-1) M with a slope of 27.3 mV decade-1 for PME and 8.0 x 10(-8)-5.0 x 10(-2) M with a slope of 29.1 mV decade-1 for CGE) and very low limits of detection (8.0 x 10(-6) M for PME and 5.0 x 10(-8) M for CGE). The potentiometric response is independent of the pH of the test solution in the pH range 3.0-6.0. The proposed electrodes possess very good selectivities over a wide variety of other cations, including alkali, alkaline earth, transition and heavy metal ions, the selectivity coefficients for the CGE being much improved over those for the PME. The electrodes were used as indicator electrodes in the potentiometric titration of Cu2+ and in the recovery of copper ions from wastewater.