Flow injection-pulse amperometric detection of ephedrine at a cobalt phthalocyanine modified carbon paste electrode

Direct detection of ephedrines and other underivatized amino compounds (amines, alicyclic amines, alkanolamines, and amino acids) can be carried out via electrocatalytic oxidation at a carbon paste electrode (CPE) modified with cobalt phthalocyanine (CoPC) in alkaline solution (0.10 mol L-1 NaOH). Most of the amino compounds tested could be determined using the CoPC/CPE in an amperometric flow detector. The analytical signal of ephedrine was stabilised by alternating the potential between an anodic detection potential of +0.30 V (+0.45 V for other amino compounds) applied for 220 ms and a cathodic reactivation potential of -0.30 V applied for 100 ms (potentials versus SCE). The linear response range for ephedrine was within 1-100 mumol L-1 and the detection limit was 0.8 mumol L-1 with a 100 microL sample loop and a typical sampling ra 60 h-1. The signal (oxidation peak current) reproducibility was 2-3%. The method was applied to the determination of ephedrine in pharmaceutical formulations with results comparable to those obtained with a standard spectrophotometric method.     

酞菁钴修饰碳糊电极对微量苯酚的测定

研究了苯酚在酞菁钴修饰碳糊电极上的电化学行为,提出了催化反应的机理,并以此为依据,用伏安法以酞菁钴修饰碳糊电极为工作电极测定了微量苯酚.在pH 8.7的磷酸盐缓冲溶液(PBS)中,苯酚在0.61 V(对SCE)出现一氧化峰,该峰电流与苯酚的浓度在5.0×10-7～1.0×10-4 mol/L之间呈线性关系,检出限为1.0×10-7 mol/L.此法可用于工业废水中苯酚的测定.     

Preparation of a polypyrrole electrode modified with a nickel phthalocyanine complex. Application to the determination of an antioxidant (propylgallate) in foods

In this paper a study of the electrocatalytic oxidation of propylgallate (PG) by using a polypyrrole electrode modified with tetrasulfonate nickel (II) phthalocyanine complex (Pt/PPy/NiPcTs) was carried out. Several parameters of this polymeric electrode, such as: (a) its stability in hydroorganic solution, by using an indium tin oxide (ITO) electrode and spectrophotometry; and (b) its thickness using electrochemical techniques, have been studied. In addition, several parameters affecting the PG voltammetric peak, such as pH, methanol water ratio, potential scan rate and analyte concentration, were considered. Finally, the developed method was applied to the determination of PG in spiked potato flakes and cornflakes, showing its validity.     

Voltamperometric determination of kinetin with a carbon paste modified electrode

The electrochemical behaviour of kinetin (6-furfurylaminopurine) on a carbon paste modified with OV-17 silicone electrode, is studied. The determination of kinetin is possible working in square wave voltammetric techniques, reaching limits of determination of 38.7 ng ml⁻¹. The proposed method was successfully applied to determine the cytokinin in extracts of apples (previously spiked with kinetin) and the obtained results were in accordance with the results obtained with HPLC-UV.     

Flow injection amperometric determination of acetaminophen at a gold nanoparticle modified carbon paste electrode

An amperometric detector with a gold nanoparticle modified carbon paste electrode (GNMCPE) was applied applied to flow injection analysis for the determination of acetaminophen. An obvious shift of the peak potential and increase of the current peak were observed for the GNMCPE in comparison to that of the bare carbon paste electrode. The experimental conditions, such as species of buffer, pH, flow rate, detection volume, injection volume, and injection time were investigated. Under the optimized conditions, the calibration curve was obtained over the concentration range of 0.1–80 mg L^?1 of acetaminophen with a linear correlation coefficient of 0.9994. The detection limit (3σ) was estimated to be 0.05 mg L^?1 (n?=?7). The recoveries of acetaminophen were between 98.40% and 104.1%, and the relative standard deviation varied between 1.66% and 2.74% for the different samples. This method was applied to analyze six types of tablets obtained from a local drugstore. The contents of acetaminophen were found to be 0.498, 0.323, 0.249, 0.324, 0.319 and 0.323 g of each tablet, respectively. These results are consistent with the values obtained by high performance liquid chromatography.     

Anodic stripping voltammetric determination of silver ion at a carbon paste electrode modified with carbon nanotubes

A carbon paste electrode (CPE) was modified with multi-wall carbon nanotubes and successfully applied to the determination of silver ion by differential pulse anodic stripping voltammetry. Compared to a conventional CPE, a remarkably improved peak current response and sensitivity is observed. The analytical procedure consisted of an open circuit accumulation step for 2?min in ?0.4?V, this followed by an anodic potential scan between +0.2 and?+?0.6?V to obtain the voltammetric peak. The oxidation peak current is proportional to the concentration of silver ion in the range from 1.0?×?10^?8 to 1.0?×?10^?5?mol?L^?1, with a detection limit of 1.8?×?10^?9?mol?L^?1 after an accumulation time of 120?s. The relative standard deviation for 7 successive determinations of Ag(I) at 0.1???M concentration is 1.99%. The procedure was validated by determining Ag(I) in natural waters.

Voltammetric determination of traces of cobalt(II) with a chemically modified carbon paste electrode

Summary A new preconcentration and voltammetric determination method for cobalt(II) in aqueous solution with a chemically modified electrode is proposed. The accumulation behaviour and voltammetry of cobalt(II) has been investigated with a carbon paste electrode modified with cationexchanger and 1,10-phenanthroline. The electrochemical response is characterized with respect to carbon paste composition, pH, preconcentration time, cobalt(II) concentration and other variables. For a 3-min preconcentration time, the electrode gives good linearity for 1×10^–7 to 4×10^–6 mol/l Co(II), a detection limit of 8×10^–8 mol/l. The response can be reproduced with a 4.0% relative standard deviation. The method is fairly free from many coexisting ions interferences. A rapid and convenient renewal procedure allows the use of a single electrode in multiple analytical determinations over several days. Satisfactory results are obtained for the determination of cobalt in a variety of certified standard reference materials.     

Potentiometric stripping determination of nickel at a dimethylglyoxime-containing graphite paste electrode

Potentiometric stripping determination of nickel(II) can be performed at zero current with a graphite paste electrode chemically modified with dimethylglyoxime. Among oxidants investigated, atmospheric oxygen present in solution was selected as the best, providing sharp and reproducible analytical signals.     

Sensitive voltammetric determination of rutin at an ionic liquid modified carbon paste electrode

An ionic liquid modified carbon paste electrode (IL/CPE) had been fabricated by using hydrophilic ionic liquid 1-amyl-3-methylimidazolium bromide ([AMIM]Br) as a modifier. The IL/CPE was characterized by scanning electron microscope and voltammetry. Electrochemical behavior of rutin at the IL/CPE had been investigated in pH 3.29 Britton-Robinson (B-R) buffer solution by cyclic voltammetry (CV) and square wave voltammetry (SWV). The experimental results suggested that the modified electrode exhibited an electrocatalytic activity toward the redox of rutin. The electron transfer coefficient (α) and the standard rate constant (k_s) of rutin at the modified electrode were calculated. Under the selected conditions, the reduction peak current was linearly dependent on the concentration of rutin in the range of 4.0 × 10⁻⁸ to 1.0 × 10⁻⁵ mol L⁻¹ (r = 0.9998), with a detection limit of 1.0 × 10⁻⁸ mol L⁻¹ (S/N = 3). The relative standard deviation (R.S.D.) for six times successful determination of 8.0 × 10⁻⁷ mol L⁻¹ rutin was 1.2%. The proposed method was applied to determine rutin in tablet and urine sample. In addition, the IL/CPE exhibited a distinct advantage of simple preparation, surface renewal, good reproducibility and good stability.     

Voltammetric determination of azithromycin at the carbon paste electrode

Azithromycin (AZ) is the first member of a class of macrolide azalides antibiotics called azolides. A simple and selective square-wave voltammetric (SWV) method has been developed for the determination of azithromycin in pure form, in pharmaceutical preparation and in biological samples. Determination of azithromycin was accomplished with hand-make carbon paste electrode (CPE) in oxidative screen mode. The counter and reference electrodes were a Pt wire and a Ag/AgCl, respectively. Various parameters that can influence the peak signal (effect of buffer, ionic strength, accumulation time, pH and the composition of the paste) have been scrutinized. The best results were obtained in acetonitrile—aqueous 1 M sodium acetate-acetic acid buffer (pH 4.6) containing 0.1 M KCl (1:9; v/v) using a 15% paraffin oil CPE. The limits of detection and quantification of the pure drug are 0.463 and 1.544 ppb (with the correlation coefficient, r=0.9785and the standard deviation, S.D.=0.1 (n=5), for the accumulation time of 60 s), respectively. The method was successfully applied to the determination of the drug in urine and two forms of pharmaceutical formulations. Recoveries were 99.2—100.5% with S.D.=0.1—and 0.8% (n=5).     

Stripping voltammetric determination of platinum metals at a carbon paste electrode modified with cationic surfactants

In this contribution, a novel method is described for the determination of platinum metals. The procedure developed employs a carbon paste electrode modified in situ with cationic surfactants of the quaternary ammonium salt type. The pre-concentration step is based on a specific accumulation mechanism involving ion-pair formation; the detection being performed by cathodic scanning in the differential pulse voltammetric mode. Regarding the individual forms of platinum metals, the method has been found convenient for the determination of three heavy platinum metals in the form of Pt(IV), Ir(III) and Os(IV), whereas for the remaining elements (Ru, Rh, and Pd) was almost inapplicable. Platinum metals of the former group can be pre-concentrated in chloride-containing supporting media via PtCl₆²⁻, IrCl₆³⁻ and OsCl₆²⁻ complex anions, the central atom of each species being fairly reducible during the voltammetric scan. Stripping signals for both platinum and iridium were proportional to the concentration in a range of 1-10 × 10⁻⁶ M Pt(IV) and Ir(III); the response for osmium being linear within 0.1-6 × 10⁻⁷ M Os(IV) with a detection limit of about 5 × 10⁻⁹ mol l⁻¹. During optimisation, special attention was paid to the accumulation mechanism, choice of key experimental conditions, and to interference effects from foreign ions with potentially ion-pairing capabilities (AuCl₄⁻, TlCl₄⁻, CrO₄²⁻, MnO₄⁻, SCN⁻, and I⁻). The method elaborated has been tested on both model solutions and real samples of industrial waste water, showing in both cases satisfactory analytical performance.     

花旗松素在碳纳米管-离子液体修饰碳糊电极上的电催化氧化及其测定

制备了碳纳米管(MWCNTs)和疏水性离子液体N-丁基吡啶六氟磷酸盐([Bu Py]PF6)复合修饰碳糊电极(MWCNTs-[Bu Py]PF6/CPE),利用循环伏安法研究了花旗松素在MWCNTs-[Bu Py]PF6/CPE上的电化学氧化行为。结果表明,花旗松素在修饰电极上出现一对灵敏、准可逆的氧化还原峰,氧化峰电位Epa=0.60 V,还原峰电位Epc=0.24 V,△Ep=0.46 V,氧化峰电流ipa=3.96μA,还原峰电流ipc=5.03μA,ipa/ipc=0.79,表明MWCNTs-[Bu Py]PF6/CPE对花旗松素具有良好的电催化氧化作用。用差分脉冲伏安法(DPV)测得花旗松素的氧化峰电流ipa与浓度c在1.2×10-5~4.0×10-2g·L-1范围内呈良好线性,检出限为2.2×10-6g·L-1。该法用于水红花子中花旗松素含量的测定,RSD为1.1%~1.5%,加标回收率为97.3%~101.3%。     

Voltammetric determination of mifepristone at a DNA-modified carbon paste electrode

A new strategy for the preparation of a DNA-modified carbon paste electrode is developed. It is found that the anodic response of mifepristone is greatly enhanced at the dsDNA-modified carbon paste electrode comparing with that obtained at the bare electrode, while the response at a ssDNA-modified electrode is similar to bare electrode. So the dsDNA-modified electrode is employed as a sensitive biosensor for the detection of mifepristone. A linear dependence of the peak currents on the concentration is observed in the range 2.0 x 10(-7) approximately 2.0 x 10(6) mol/L, with a detection limit of 1.0 x 10(-7) mol/L. The relative standard deviation is 4.3% for six successive determinations of 1.0 x 10(6) mol/L mifepristone. The determination of mifepristone tablets is carried out and satisfactory results are obtained.     

Stripping voltammetric determination of mercury(II) at antimony-coated carbon paste electrode

A new procedure was elaborated to determine mercury(II) using an anodic stripping square-wave voltammetry at the antimony film carbon paste electrode (SbF-CPE). In highly acidic medium of 1 M hydrochloric acid, voltammetric measurements can be realized in a wide potential window. Presence of cadmium(II) allows to separate peaks of Hg(II) and Sb(III) and apparently catalyses reoxidation of electrolytically accumulated mercury, thus allowing its determination at ppb levels. Calibration dependence was linear up to 100 ppb Hg with a detection limit of 1.3 ppb. Applicability of the method was tested on the real river water sample.     

Electrocatalytic behaviour of carbon paste electrode modified with iron(II) phthalocyanine (FePc) nanoparticles towards the detection of amitrole

This paper describes the construction of a carbon paste electrode (CPE) impregnated with nanoparticles of iron(II) phthalocyanine (nanoFePc). The new electrode (nanoFePc-CPE) revealed interesting electrocatalytic behaviour towards amitrole; pure catalytic diffusion-controlled process, with high Tafel slope (235 mV/decade) suggesting strong binding of amitrole with nanoFePc catalyst. The effects of catalyst loading, varying pH and electrolytes were studied. The mechanism for the interaction of amitrole with the nanoFePc is proposed to involve the Fe^(III)Pc/Fe^(II)Pc redox process. Using chronoamperometry (E = +0.42 V versus Ag/AgCl) technique, the sensor was reliably employed for amitrole assay at pH 12.0 phosphate buffer (with sodium sulphate as the supporting electrolyte) for up to 12 nM amitrole with excellent sensitivity (ca. 3.44 μA/nM) and low detection limit (3.62 ± 0.11 nM, i.e. 0.305 μg L⁻¹ using the Y_B + 3_σB criterion and 0.85 ± 0.03 nM, i.e. 70 ng/L with the Y_B + 2_σB criterion) as well as satisfactory amperometric selectivity coefficient (K_amp ≈ 7.4 × 10⁻⁴ for ammonium thiocyanate, a component of many amitrole herbicides, and 3.2 × 10⁻³ for asulam pesticide). The surface of the electrode can easily be regenerated by simple polishing on an alumina paper, obtaining a fresh surface ready for use in a new assay. The proposed electrode was successfully applied in the quantification of amitrole in its commercial formulation as well as in tap water samples.     

Chemically modified carbon paste electrode for determination of copper(II) by potentiometric method

The utility of carbon paste electrode modified with DTPT (3,4-dihydro-4,4,6-trimethyl-2(1H)-pyrimidine thione) for the potentiometric determination of Cu(II) in aqueous medium is demonstrated. The electrode exhibits linear response to Cu(II) over a wide concentration range (9.77x10(-7)-7.6x10(-2)) with Nernstian slope of 30+/-2 mV per decade. It has a response time of about 45 s and can be used for a period of two months with good reproducibility. The detection limit of this electrode was 7.0x10(-7) M. The proposed electrode shows a very good selectivity for Cu(II) over a wide variety of metal ions. This chemically modified carbon paste electrode was successfully used for the determination of Cu(II) in electronics waste sample solution.     

Mechanically immobilized nickel aquapentacyanoferrate modified electrode as an amperometric sensor for the determination of BHA

Nickel aquapentacyanoferrate (NAPCF), a novel transition metal complex has been prepared and its ability to act as an electrocatalyst for BHA oxidation has been demonstrated. The cyclic voltammetric behaviour of the NAPCF modified electrode prepared by mechanical immobilization on the graphite electrode was well defined. A pair of redox peaks corresponding to the electrochemical behaviour of the NAPCF was observed at 0.35 V and 0.31 V, corresponding to the anodic and cathodic peaks respectively, with a formal potential of 0.33 V. The NAPCF modified electrode favoured electrocatalytic oxidation of BHA to occur at a greatly minimized overpotential of 0.48 V. Experiments were performed to characterize the electrode as an amperometric sensor for the determination of BHA. The anodic peak current was linearly related to BHA concentration in the range of 6.24x10(-7) M to 2.19x10(-4) M with a detection limit of 2.49x10(-7) M and a correlation coefficient of 0.9979. Amperometry in stirred solution exhibited quick and sensitive response to BHA, showing the possible application of the modified electrode in flow system analysis. The modified electrode retained its initial response for more than 2 months when stored in supporting electrolyte, owing to the chemical and mechanical stability of the NAPCF mediator. This modified electrode was also quite effective in the determination of BHA in commercial samples.     

A study on the determination of chromium as chromate at a carbon paste electrode modified with surfactants

A procedure for the determination of chromium is described based on synergistic pre-concentration of the chromate anion at a carbon paste electrode modified in situ with quarternary ammonium salts such as 1-ethoxycarbonylpentadecyltrimethylammonium bromide (Septonex^®), cetyltrimethylammonium bromide (CTAB) or cetylpyridinium bromide (CPB). The proper electrochemical detection utilises the reduction Cr(VI) → Cr(III) performed in the differential pulse cathodic voltammetric mode. In discussion, considerable attention has been paid to the accumulation mechanism at the carbon paste electrode in the presence of surfactants. Furthermore, after optimising the corresponding experimental conditions (0.1-0.3 M HCl + 0.1 M NaCl as the supporting electrolyte, 2.5-25 μM as the total concentration of modifier, pre-concentration at +0.7 V versus Ag/AgCl and the stripping from +0.7 to −0.4 V), the analytical performance of the method has been evaluated. The signal of interest was reproducible within ±8% and proportional to the concentration in a range of 0.5-50 μM CrO₄²⁻, with a limit of detection (S/N = 3:1) of about 5×10⁻⁸ M CrO₄²⁻ (with accumulation for 300 s). Interference studies were focused mainly on the species capable of forming ion-pairs with the modifier; i.e., TlCl₄⁻, AuCl₄⁻, PdCl₄²⁻, PtCl₆²⁻, VO₄³⁻, MnO₄⁻ and I⁻. Practical applicability of the method was tested on model solutions via the recovery rates (typically 90-110%) or using selected certified reference materials (tea, bush leaves, clover) and two samples of black tea when the respective results were compared to those obtained by the reference determinations with ICP-AES.     

离子液体BMIMPF6修饰碳糊电极电化学测定维生素E

用疏水性离子液体1-丁基-3-甲基咪唑六氟磷酸([BMIM]PF6)作粘合剂制备了离子液体修饰碳糊电极(IL/CPE)。采用循环伏安法(CV)研究了维生素E(vitamin E,VE)的氧化产物生育酚红在IL/CPE和未修饰碳糊电极(CPE)上的电化学行为,结果表明生育酚红在IL/CPE上氧化过程更易于进行,峰电流响应ip也明显增加,表明IL/CPE对生育酚红的氧化还原反应具有良好的电催化作用。同时测定了电极过程的动力学参数:电荷转移系数α=0.8746,扩散系数D=1.65×10-3cm2/s,电极反应速率常数kf=6.64×10-2cm/s。采用方波伏安法(SWV)发现生育酚红氧化峰电流与其浓度在1.53×10-4mol/L～8.39×10-7mol/L范围内呈线性关系,检出限为1.58×10-8mol/L。该法可用于VE实际样品的分析测定。