Adsorptive stripping voltammetric determination of azithromycin at a glassy carbon electrode modified by electrochemical oxidation.

The adsorptive and electrochemical behaviors of azithromycin were investigated on a glassy carbon electrode that was electrochemically treated by anodic oxidation at +1.8 V, following potential cycling in the potential range from -0.8 to +1.0 V. The resulting electrode showed good activity to improve the electrochemical response of the drug. An adsorptive stripping voltammetric method for the determination of azithromycin at an electrochemically activated glassy carbon electrode has been developed. Azithromycin was accumulated in phosphate buffer, pH 6, at a potential of +0.3 V (vs. Ag/AgCl electrode) for a certain time, and then determined by differential pulse voltammetry. The oxidative peak current at +0.82 V, at a scan rate of 20 mV s(-1), was a linear function of the concentration in the ranges of 0.25 - 2 microg mL(-1) and 1 - 10 microg mL(-1) using a 240 or 60 s(-1) preconcentration time, respectively. Application of the method to the determination of azithromycin in pharmaceuticals resulted in an acceptable deviation from the stated concentration. The preconcentration medium-exchange approach was utilized for the selective determination of the drug in spiked urine samples with satisfactory results. The peak current was linear with the drug concentration in the range of 0.5 - 3.5 microg per mL urine. The detection limit was 0.2 microg mL(-1) urine. The recovery levels of the method reached 96.3%.     

Comparative characterization of two techniques for selenium(IV) preconcentration on a film mercury electrode with the use of an automated solution replacement system without circuit disconnection

Two versions of selenium(IV) preconcentration and determination on a mercury film electrode (MFE) by cathode stripping voltammetry with an automated solution replacement system without circuit disconnection are compared. In one version, selenium(IV) is preconcentrated together with copper(II); in the other, selenium is preconcentrated on a copper-modified MFE. Under optimum conditions (against the 0.1 M HCl background at selenium electrolysis potentials from ?350 to ?400 mV and electrolysis times of 180–300 s), calibration curves for both selenium preconcentration versions are linear over the concentration ranges from 2.5 to 20 μg/L and from 50 to 250 mg/L. The selenium peak heights are well reproduced in both cases (in the range of the concentrations studied, S _r lie in the range from 0.02 to 0.05). Sequential copper and selenium preconcentration is more convenient: there is no need to add copper to each analyzed solution, and it is possible to optimize selenium preconcentration parameters (solution composition, electrolysis potential, and electrolysis time) regardless of the copper preconcentration parameters.     

Square-wave adsorptive cathodic stripping voltammetric determination of anti-inflammatory indomethacin drug in tablets and human serum at a mercury electrode

Indomethacin is a non-steroidal anti-inflammatory drug possessing anti-pyretic and analgesic properties. A fully validated square-wave adsorptive cathodic stripping voltammetric procedure is described for determination of indomethacin. The procedure was based on the reduction of the C=O double bond of the drug molecule in Britton-Robinson buffer (pH 4) after its preconcentration onto the mercury electrode surface. The optimized conditions of the procedure were: frequency 120 Hz, scan increment 10 mV, pulse amplitude 50 mV, preconcentration potential -0.9 V (vs. Ag/AgCl/KCl(s)) and preconcentration time 90 s. The proposed procedure was successfully applied for determination of the drug in tablets and human serum with good recoveries. The limits of detection in bulk form and human serum were 6.7 x 10(-10) mol L(-1) and 8.1 x 10(-10) mol L(-1), respectively.     

Determination of low cadmium concentrations in wine by on-line preconcentration in a knotted reactor coupled to an inductively coupled plasma optical emission spectrometer with ultrasonic nebulization

An on-line cadmium preconcentration and determination system implemented with inductively coupled plasma optical emission spectrometry (ICP-OES) associated to flow injection (FI) with ultrasonic nebulization system (USN) was studied. The cadmium was retained as the cadmium-2-(5-bromo-2-pyridylazo)-5-diethylaminophenol, Cd-(5-Br-PADAP), complex, at pH 9.5. The cadmium complex was removed from the knotted reactor (KR) with 3.0 mol/L nitric acid. A total enhancement factor of 216 was obtained with respect to ICP-OES using pneumatic nebulization (12 for USN and 18 for KR) with a preconcentration time of 60 s. The value of the detection limit for the preconcentration of 5 mL of sample solution was 5 ng/L. The precision for 10 replicate determinations at the 5 microg/L Cd level was 2.9% relative standard deviation (RSD), calculated from the peak heights obtained. The calibration graph using the preconcentration system for cadmium was linear with a correlation coefficient of 0.9998 at levels near the detection limits up to at least 1,000 microg/L. The method was successfully applied to the determination of cadmium in wine samples.     

测定人发中铜的桑色素修饰碳糊电极吸附溶出伏安法

制作了用桑色素作修饰剂的化学修饰碳糊电极,利用该电极为工作电极,建立了测定痕量铜的新方法。在甲酸钠－盐酸缓冲溶液（pH4.6）中,在0.20V（vsSCE）下搅拌富集,铜（Ⅱ）与碳糊修饰电极表面的桑色素形成电活性络合物而吸附富集于电极表面,经－0.45V静置还原后,阳极化线性扫描,在－0.05V获得一灵敏的二次导数溶出峰。在不同富集时间下,其二次导数峰电流与铜（Ⅱ）浓度分别在1.0×10     

银掺杂聚L-甲硫氨酸修饰电极同时测定对苯二酚和邻苯二酚

用循环伏安法制备了银掺杂聚L-甲硫氨酸修饰玻碳电极,研究了对苯二酚和邻苯二酚在该修饰电极上的电化学行为,建立了同时测定对苯二酚和邻苯二酚的新方法.研究发现,在pH=5.0的磷酸盐缓冲溶液中,扫速为100 mV/s时,对苯二酚和邻苯二酚在银掺杂聚L-甲硫氨酸修饰玻碳电极上均出现1对氧化还原峰,峰电位分别为:Epa=0.228 V、Epc =0.162 V和Epa=0.347 V、Epc =0.287 V,二者的氧化峰电位差达119 mV,还原峰差达125 mV.在最佳的条件下,用差分脉冲伏安法同时测定邻苯二酚和对苯二酚的线性范围为3.00 ×10-6～1.00 ×10-4mol/L,检出限为8.0×10-7 mol/L(对苯二酚)和5.0×10-7 mol/L(邻苯二酚).此法用于废水样中对苯二酚和邻苯二酚的测定,获得满意结果.     

Determination of molybdenum in the presence of 2-(2-benzothiazolylazo)-p-cresol by catalytic-adsorptive stripping voltammetry

The adsorptive collection of the molybdenum (VI) complexed with 2-(2-benzothiazolylazo)-p-cresol (BTAC) coupled with the catalytic current of the adsorbed complex at a static mercury drop electrode yields an ultrasensitive voltammetric procedure for the determination of molybdenum. Optimal experimental conditions were: a stirred acetate buffer 0.2 M (pH 3.5) as supporting electrolyte, a BTAC concentration of 1.0 x 10(-6) M as ligand, and a concentration of 0.1 M potassium nitrate as the oxidizing agent. In addition, a preconcentration potential of -0.080 V vs Ag/AgCl (3 M KCl), equilibration time of 15 s, a frequency of 30 Hz, a scan increment of 2 mV, a pulse amplitude of 0.050 mV, and a drop area of 0.032 cm2 were used. The cyclic voltammogram was recorded using a staircase wave with a scan rate of 100 mV/s. The forward scan starts at the initial potential of -0.080 V and is reversed at -0.90 V. Using the catalytic current at approximately -0.55 V the response to the Mo(VI) was found to be linear over a concentration range of 1.0-10.0 microg/L. The limit of detection is as low as 6.2 x 10(-10) M with 4 min of preconcentration time. The possible interference of other trace ions was investigated. The merits of this procedure are demonstrated using of reference samples.     

1-(3-硝基苯基)-3-[4-(苯基偶氮)苯基]-三氮烯修饰碳糊电极测定痕量锡

制备了三氮烯修饰碳糊电极(m-NPPAPT/CPE),并研究了Sn(Ⅱ)在该电极上的吸附伏安行为,建立了一种测定痕量锡(Ⅱ)的新方法。采用二阶导数线性扫描溶出伏安法进行分析。结果表明:在1mL 0.5mol/L HCl溶液中,于-1200mV处搅拌富集一定时间,在-1200～-200mV范围内以150mV/s的扫描速度线性扫描,Sn(Ⅱ)吸附在修饰电极表面,于约-476mV(vs SCE)处产生一个灵敏的阳极溶出峰,峰电流比未修饰电极增大约11倍。其峰电流与Sn(Ⅱ)浓度在4.0×10-10～1.0×10-8 mol/L和1.0×10-8～4.0×10-6 mol/L范围内分两段呈良好线性关系,其线性回归方程分别为ip(μA)=1.646C(μmol/L)+2.9566和ip(μA)=52.804C(μmol/L)-0.6402,相关系数分别为0.9973和0.9967;检出限(S/N=3)为2.7×10-10 mol/L(富集时间120s)。本方法操作简便、灵敏度高,应用于罐头食品中锡含量的测定,结果满意。     

A square-wave adsorptive stripping voltammetric method for the determination of Amaranth, a food additive dye

Square-wave adsorptive stripping voltammetric (AdSV) determinations of trace concentrations of the azo coloring agent Amaranth are described. The analytical methodology used was based on the adsorptive preconcentration of the dye on the hanging mercury drop electrode, followed by initiation of a negative sweep. In a pH 10 carbonate supporting electrolyte, Amaranth gave a well-defined and sensitive AdSV peak at -518 mV. The electroanalytical determination of this azo dye was found to be optimal in carbonate buffer (pH 10) under the following experimental conditions: accumulation time, 120 s; accumulation potential, 0.0 V; scan rate, 600 mV/s; pulse amplitude, 90 mV; and frequency, 50 Hz. Under these optimized conditions the AdSV peak current was proportional over the concentration range 1 x 10(-8)-1.1 x 10(-7) mol/L (r = 0.999) with a detection limit of 1.7 x 10(-9) mol/L (1.03 ppb). This analytical approach possessed enhanced sensitivity, compared with conventional liquid chromatography or spectrophotometry and it was simple and fast. The precision of the method, expressed as the relative standard deviation, was 0.23%, whereas the accuracy, expressed as the mean recovery, was 104%. Possible interferences by several substances usually present as food additive azo dyes (E110, E102), gelatin, natural and artificial sweeteners, preservatives, and antioxidants were also investigated. The developed electroanalyticals method was applied to the determination of Amaranth in soft drink samples, and the results were compared with those obtained by a reference spectrophotometric method. Statistical analysis (paired t-test) of these data showed that the results of the 2 methods compared favorably.     

Application of nanoperlite as a new natural sorbent in the preconcentration of three organophosphorus pesticides by microextraction in packed syringe coupled with gas chromatography and mass spectrometry

A rapid, low‐cost, and simple method is proposed based on a miniaturized solid‐phase extraction named microextraction in packed syringe coupled with gas chromatography and mass spectrometry for the preconcentration and determination of some organophosphorous pesticides including diazinon, ethion, and malathion. For the first time, natural nanoperlite is used as a safe sorbent. Based on this technique, the analytes are adsorbed on the solid phase and then eluted by a desorbing solvent. The influence of some important parameters such as the solution pH, type, and volume of the organic desorption solvent on the microextraction efficiency of the selected pesticide technique is investigated. The proposed method showed a good linearity in the range of 1.0–35.0 μg/L for ethion and 0.4–30.0 μg/L for both diazinon and malathion. The limits of detection in the range of 0.1–0.38 μg/L were obtained using the selected ion‐monitoring mode of the mass spectrometer. The reproducibility of the method was found to be in the range of 2.8–8.9% for the studied pesticides. To evaluate the matrix effect, the developed method is also applied to the preconcentration and determination of the selected pesticides in real water samples.     

Trace Determination of Zirconium（Ⅳ） by Anodic Adsorptive Voltammetry at a Carbon Paste Electrode

A new sensitive adsorptive voltammetric method was described for the determination ofzirconium at a carbon paste electrode (CPE) in the presence of alizarin complexone (ALC).Optimal analytical conditions are: 1.0~ l0“6 or 5.0x l0“7 mol/L ALC, 0.20 mol/L HAC-NaAc (pH4.3), accumulation for 60 s at 0 V (vs. SCE), and linear scanning from 0 V to 1.0 V at 250 mV/s.The peak potential of the complex is at 0.81 V. By using a model JP-303 polarographic analyzer,2.0~ l0l~ mol/L (S/N=3) zirconium can be detected with a 90 s accumulation, when the 2nd-orderderivative linear sweep technique is used, and the linear range is 6.0~ 10l~-2.0~ l0s mol/L (5.0~ l07mol/L ALC) and 2.0~108-2.0~ l07 mol/L (1.0~ 10.6 mol/L ALC), respectively. The developedmethod was applied to the determination of trace zirconium in the ore samples with satisfactoryresults.     

Catalytic-voltammetric determination of the antioxidant tert-butylhydroxyanisole (BHA) at a nickel phthalocyanine modified carbon paste electrode

The voltammetric behaviour of the antioxidant tert-butylhydroxyanisole (BHA), at a carbon paste electrode modified with the electron mediator nickel phthalocyanine, is described, and a method for the determination of this antioxidant, based on its oxidation on the modified electrode, is proposed. Cyclic voltammograms showed a well-defined oxidation peak for BHA slightly shifted towards less positive potentials with respect to that obtained at the plain carbon paste electrode. The peak current measured at the modified electrode is considerably higher than that obtained at the unmodified electrode. A modifier percentage of 2%, a methanol percentage of 2% and a 0.1 mol/HClO(4) medium were chosen as working conditions. The i(p)vs v1 2 plot obtained by linear sweep voltammetry showed a linear relationship over the whole scan rate range studied (5-2000 mV/sec) which is typical of a diffusion-controlled current. Using differential pulse voltammetry at DeltaE = 50 mV, linear calibration graphs were obtained in the concentration ranges 1.0-30.0, 0.10-1.0 and 0.02-0.10 mg/l BHA. The detection limit was 0.0036 mg/l (2.0 x 10(-8) mol/l). Interferences from other substances commonly present in commercial antioxidant mixtures were tested. The developed method was applied to the determination of BHA in spiked potato flakes.     

Square wave Stripping voltammetry of Cobalt Based on Adsorptive accumulation of its Hydroxynaphthol Blue (HNB) Complex at the Static Mercury Drop Electrode

ABSTRACT

A new method is described for the determination of cobalt based on the square wave adsorptive stripping voltammetry of Co(II) complexed with hydroxynaphthol blue (HNB) at the static mercury drop electrode. Optimal conditions were found to be: preconcentration potential, -0.500V vs. Ag/AgCl (KCl 3M); preconcentration time, 30 s (with stirring); pulse height, 50 mV; frequency, 100 Hz; scan increment, 4 mV; step time, 0.010 s; supporting electrolyte, HEPES/HCl (0.1 M, pH 7.0-8.0) or triethanolamine/HCl (0.1 M, pH 7.6); concentration of hydroxynaphthol blue, 5.0 × 10^?6 M. The response of the system was found to be linear in a range of Co(II) concentrations from 2.0 to 10.0 μg/L. The limit of detection was found to be 1.8 × 10^?9 M with 2 minutes of preconcentration time. The effect of various potential interferences were also studied including a variety of cations, anions and organic surfactants. The interferences by Ni(II), and Cr(VI) may be eliminated by addition of EDTA or CDTA and the of Fe(III) and Ti(IV) by fluoride. The merits of the procedure were demonstrated in the analysis of certified and biological samples.     

银掺杂聚L-天冬氨酸修饰电极的制备及对多巴胺的测定

利用循环伏安法将银与L-天冬氨酸聚合修饰在玻碳电极表面,制成银掺杂聚L-天冬氨酸修饰电极,研究了多巴胺在此电极上的电化学行为,建立了循环伏安法测定多巴胺的新方法.在磷酸盐缓冲溶液(PBS, pH 7.0)中,扫描速率为50 mV/s时,多巴胺在修饰电极上产生一对氧化还原峰,Epa=0.191 V,Epc=0.161 V.用循环伏安法进行测定时,峰电流与多巴胺浓度分别在3.0×10-7 ～1.0×10-5 mol/L和1.0×10-5 ～5.0×10-4 mol/L内呈良好的线性关系; 检出限为5.0×10-8 mol/L.用于药物和尿样中多巴胺的测定,结果满意.     

维生素B1的电化学聚合及催化作用

用循环伏安法在石墨电极上制备了VB1聚合膜修饰电极,VB1聚合膜在pH5的PBS中有一对氧化还原峰,峰电位Epd=350mV,Epc=325mV,峰电流与扫描速率的平方根成正比,表明电子在膜中的传递为扩散控制,且聚合膜与VB1单体有不同的电化学性质。实验表明VB1聚合膜对多巴胺、肾上腺素等神经递质有显著的电催化作用。     

On-line complexation of zinc with 5-Br-PADAP and preconcentration using a knotted reactor for inductively coupled plasma atomic emission spectrometric determination in river water samples

An on-line zinc preconcentration and determination system implemented with inductively coupled plasma atomic emission spectrometry (ICP-AES) associated with flow injection (FI) was studied. The zinc was retained as zinc-2-(5-bromo-2-pyridylazo)-5-diethylaminophenol (Zn-(5-Br-PADAP)) complex at pH 9.2. The zinc complex was removed from the knotted reactor (KR) with 30% v/v nitric acid. An enrichment factor of 42 was obtained for the KR system with respect to ICP-AES using pneumatic nebulization. The detection limit for the preconcentration of 10 mL of aqueous solution was 0.09 microg/L. The precision for 10 replicate determinations at the 5 microg/L Zn level was 2.3% relative standard deviation (RSD), calculated with the peak heights obtained. The calibration graph using the preconcentration system for zinc was linear with a correlation coefficient of 0.9997 at levels near the detection limits up to at least 100 microg/L. The method was succesfully applied to the determination of zinc in river water samples.     

Anodic square-wave stripping voltammetric analysis of epinephrine using carbon fiber microelectrode

The behavior of epinephrine on a carbon fiber microelectrode (CFME) was studied with cyclic voltammetry and square-wave (SW) stripping voltammetry in order to find optimum conditions for its analysis using the CFME. An anodic stripping peak at about 0.20 V (vs. Ag/AgCl) was utilized. Under optimum conditions for anodic stripping (a pH value of 7.4, a deposition potential of − 0.5 V, a deposition time of 90 s, a final potential of 0.8 V, a SW frequency of 20 Hz, a step potential of 5 mV, and an amplitude of 45 mV), the calibration was linear in the concentration range of 0.0∼0.4 mg/L, and the detection limit was found to be 0.009 mg/L with a relative standard deviation 0.18% (n = 12) at 0.2 mg/L. The analytical performance of the CMFE, which is unmodified, is comparable to or better than other voltammetric results with various modified electrodes.     

Quantification,dissipation behavior and risk assessment of ethion in green pea by gas chromatography‐electron capture detector

Residue investigation was carried out to scrutinize the persistence, dissipation behavior, half‐life, and risk assessment of ethion on green pea fruit by spraying ethion at the fruiting stage followed by another application at 10 day intervals. The samples were extracted by using a quick, easy, low‐cost, effective, rugged, and safe method, and the residues of ethion were analyzed by gas chromatography with electron capture detection. Here we report a novel, accurate, and cost‐effective gas chromatography method for the determination of average deposits of ethion on green pea. The initial deposits were found to be 4.65 mg/kg following the application of insecticide. Residues of ethion reached below the detection limit of 0.10 mg/kg after 25 days at recommended dosage. The half‐life of ethion was found to be 4.62 days. For risk assessment studies, the 25th day will be safe for consumers for the consumption of green peas. The developed method is simple, sensitive, selective, and repeatable and can be extended for ethion‐based standardization of herbal formulations containing green pea and its use in pesticide industries.     

多壁碳纳米管修饰电极阳极溶出法测定痕量锌

报道了自制的多壁碳纳米管修饰电极测定锌离子的电分析方法。在浓度0.20mol/L的乙酸钠溶液中,以此修饰电极作为工作电极,以-1.50V为富集电位,150s为富集时间,用方波伏安溶出法(起始电位:-1.5V;终止电位:-0.8V;电位增量:0.01V;振幅:0.05V;频率:5Hz)测定-1.30V处的峰电流,用峰高定量。结果表明,该电极对锌离子吸附的灵敏度较高;当锌离子浓度为1.0×10-6～9.0×10-6mol/L时,线性关系好,相关系数为0.9992;对自来水样本进行了测定,取得了满意的结果,加标回收率在97%～105%之间。     

Validation of a capillary electrophoresis method for the simultaneous determination of amlodipine besylate and valsartan in pharmaceuticals and human plasma

A rapid, simple, and sensitive capillary electrophoresis (CE) method was developed and validated for the simultaneous determination of amlodipine (AML) and valsartan (VAL) in pharmaceuticals and human plasma using a UV photodiode array detector. Electrophoretic conditions were optimized to improve separation, sensitivity, and rapidity. The optimal conditions were 25 mM phosphate buffer at pH 8.0, injection time 10.0 s, voltage 25 kV, and column temperature 25 degrees C, with detection at 214 nm. The method was found to be linear in the range of 1.0-35 and 1.0-350 mg/L, with weighted regression 0.9999 and 0.9994, for AML and VAL, respectively. Validation of the method showed acceptable intraday and interday accuracy (85.5-95.3%) and precision (RSD 1.64-4.2%) in pharmaceutical formulation and human plasma analysis. The sensitivity of the method was enhanced by both optimization of the CE procedure and preconcentration performed by liquid-liquid extraction. The LOD for both AML and VAL was 0.03 mg/L, which allows analysis at the level of the drugs possibly found in human plasma. Therefore, the proposed method is suitable for QC in pharmaceutical laboratories and therapeutic drug monitoring in clinical laboratories.