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.     

Electrochemical behavior of valsartan and its determination in capsules

Electrochemical behavior of valsartan has been carried out in Britton-Robinson (B-R) buffer solution at pH 7.0 at the mercury film electrode (MFE) by cyclic, linear sweep, differential-pulse and square-wave voltammetry. The property of valsartan adsorption at the MFE using accumulation potential of +0.10 V was observed. The effects of experimental parameters on electrochemical process at the MFE were discussed. Differential-pulse adsorptive stripping and square-wave adsorptive stripping voltammetry for the valsartan determination were proposed, linearity was found in the range of 6.0 x 10(-8) to 4.0 x 10(-6)mol/L. The detection limits were 2.93 x 10(-9) and 3.27 x 10(-9)mol/L, respectively. The proposed methods were also applied to the commercial valsartan with good recoveries.     

Adsorptive stripping voltammetric determination of vanadium as chloranilic acid complex

Traces of vanadium(V) can be determined up to 21 ng/l by adsorptive stripping voltammetry using 2,5-dichloro-1,4-dihydroxy-3,6-benzoquinone (chloranilic acid) as complex forming reagent. The complex is stable in a 0.1 mol/l acetate buffer (pH 4.6) solution and adsorbed at the electrode surface in a potential range between –150 mV and –400 mV. The adsorption process is solved by alternating current (ac) voltammetric measurements. The method is applied to different real samples.     

Adsorptive Stripping Square-Wave Voltammetry of Creatine

ABSTRACT

An adsorptive stripping square-wave voltammetric method for quantitative determination of creatine is developed. The basic redox properties of creatine are investigated by means of square-wave and cyclic staircase voltammetry. Creatine undergoes an irreversible reduction in neutral and acidic medium at a hanging mercury drop electrode. The square-wave voltammetric response of creatine depends on the parameters of the SW excitation signal as well as on the concentration and type of the supporting electrolyte, the accumulation time and the potential and pH of the medium. The optimal experimental conditions for quantitative determination of creatine are as follows: supporting electrolyte 0.1 mol/L KNO₃ buffered with 0.1 mol/L acetate buffer to pH = 4 and accumulation potential -1.2 V. The optimal SW parameters found are: frequency f = 120 Hz, amplitude E _sw = 30 mV, and scan increment dE = 4 mV. A detection limit of 6.6 x 10^?8 mol/L creatine was obtained after 30 s preconcentration period at accumulation potential -1.2 V. The correlation coefficients of the calibration curves at concentration levels of 10^?7 to 10^?5 mol/L creatine are greater than 0.99. The results of recovery tests range from 92.18% to 102.51%.     

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 synthetic food dyes by capillary electrophoresis

A method for the determination of synthetic tar dyes used as food additives using capillary electrophoresis with photodiode-array detection was investigated. The dyes Erythrosine (R-3), Phloxine (R-104), Rose Bengal (R-105), Acid Red (R-106), Amaranth (R-2), New Coccine (R-102) and Allura Red AC (R-40) were separated on a capillary column (50 cm × 75 μm I.D.) and identified from the absorbance spectra of each peak. The electrophoresis buffer used was a mixture of 25 mM sodium phosphate buffer and 25 mM sodium borate buffer (1:1) (pH 8.0) containing 10 mM sodium dodecyl sulfate (SDS). Substitution of β-cyclodextrin for SDS in the electrolyte buffer was effective for the separation of R-2 and R-102. This modified method could be employed as an additional assay method for these two dyes.     

Comparison of Electrochemical Behavior of Hydroxyl‐substituted and Nonhydroxyl‐substituted Azo Dyes at a Glassy Carbon Electrode

The voltammetric behaviour of four azo dyes has been compared at a glassy carbon electrode. It is shown that the azo dyes (e.g. Reactive Brilliant Red x‐3b (RBR x‐3b), Acid Red 6b (AR 6b)) with a hydroxyl group in the ortho position with respect to the azo bridge give rise to well defined, irreversible peaks for the oxidation and reduction process within a pH range of 2–12. In the case of the non‐hydroxyl azo dye (e.g. Reactive Yellow x‐rg (RY x‐rg)), or azo dye with a meta hydroxyl group (e.g. Reactive Orange x‐gn (RO x‐gn)), the oxidation was comparatively tougher, and the peak was not clear or even invisible in the accessible potential range. The mechanism of electrochemical oxidation of RBR x‐3b, as well as AR 6b is proposed. The reduction steps were only accessible when pH < 8 for RY x‐rg and RO x‐gn dye compounds. For the hydroxyl‐substituted dyes, re‐oxidation peaks were obtained in the subsequent scan, owing to the oxidation of reduction products‐amine or hydroazo intermediates.     

阳极吸附伏安法测定盐酸莫西沙星

提出了阳极吸附伏安法测定盐酸莫西沙星的方法。在pH 6.55的B-R缓冲溶液中,开路富集120s后,盐酸莫西沙星在碳糊电极表面于0.987V(vs.SCE)处产生一灵敏的氧化峰,该氧化峰电流与盐酸莫西沙星浓度在5.6×10-7～1.0×10-5 mol.L-1范围内呈线性关系,其检出限(3s/k)为4.3×10-8 mol.L-1。方法用于模拟片剂样品中盐酸莫西沙星的测定,测定值与标示值相符,其相对标准偏差(n=6)为3.8%,以健康人尿液为基体做加标回收试验,测得平均回收率为101.6%。     

Determination of Trace Copper by Adsorptive Voltammetry Using a Multiwalled Carbon Nanotube Modified Carbon Paste Electrode

A new method for the determination of trace copper was described. A multiwalled carbon nanotube modified carbon paste electrode was prepared and the adsorptive voltammetric behavior of copper‐alizarin red S (ARS) complex at the modified electrode was investigated. By use of the second‐order derivative linear sweep voltammetry, it was found that in 0.04 mol/L acetate buffer solution (pH 4.2) containing 4×10^?6 mol/L ARS, when accumulation potential is 0 mV, accumulation time is 60 s and scan rate is 100 mV/s, the complex can be adsorbed on the surface of the electrode, yielding one sensitive reduction peak at ?172 mV (vs. SCE). The peak current of the complex is proportional to the concentration of Cu(II) in the range of 2.0×10^?11–4.0×10^?7 mol L^?1 with a detection limit (S/N=3) of 8.0×10^?12 mol/L (4 min accumulation). The proposed method was successfully applied to the determination of copper in biological samples with satisfactory results, the recoveries were found to be 96%–102%.     

Adsorptive stripping voltammetric measurements of trace levels of uranium following chelation with mordant blue 9

The chelate of uranium with the azo dye Mordant Blue 9 is shown to be adsorbed and then reduced on the hanging mercury drop electrode. These properties have been exploited in developing a highly sensitive stripping voltammetric procedure for trace determination of uranium. With controlled adsorptive accumulation for 5 min, a detection limit near 2 x 10(-10)M uranium is obtained. Cyclic voltammetry has been used to characterize the interfacial and redox behaviour. The effect of various operational parameters on the stripping response is discussed. Experimental conditions include use of 1 x 10(-6)M Mordant Blue 9 in 0.05M acetate buffer (pH 6.5), an accumulation potential of -0.43 V, and a linear potential scan. The response is linear up to 1.2 x 10(-7)M uranium, and the relative standard deviation at 4.2 x 10(-8)M is 3.2%. The effects of possible interferences from organic surfactants or metal ions have been investigated.     

LC/MS method using cloud point extraction for the determination of permitted and illegal food colors in liquid, semiliquid, and solid food matrixes: single-laboratory validation

A cloud point extraction method is reported using LC/MS for the determination of regulated water-soluble food colors (Allura Red, Sunset Yellow, erythrosine, and tartrazine) and banned fat-soluble synthetic azo dyes (Sudan I, II, III, and IV; Red B; 7B; Black B; Red G; Metanil Yellow; and Rhodamine B). The extraction of all 14 colors was carried out with cloud point extraction using the nonionic surfactant Triton X 114. Optimized conditions for cloud point extraction were 3% Triton X 114 (w/v), 0.1 M ammonium acetate, and heating at 50 degrees C for 30 min. This approach proved effective in giving quantitative recoveries from a diverse range of food matrixes, and optimized LC gave baseline chromatographic separation for all colors including Sudan IV and Red B. Single-laboratory validation was performed with spiking into liquid matrixes (wine and homemade wine), semiliquid matrixes (sauce and homemade paprika paste), and solid matrixes (spice and homemade chili powder) using the respective blank matrixes for matrix-matched calibration. The LOQ values for water-soluble colors were in the range of 15-150 mg/kg, and for the fat-soluble colors, 0.1-1.5 mg/kg. The mean recovery values were in the range of 69.6-116.0% (except Allura Red and Sunset Yellow in wine, for which recoveries were lower). The mean RSDs for colors were in the range of 4.0-14.8%. A small survey was conducted of samples of confectionery products, dried fruits, wines, bitter sodas, juices, sauces, pastes, and spices, which demonstrated the applicability of the method to a diverse selection of real food samples. Allura Red was detected in strawberry jelly and Sunset Yellow in artificial saffron.     

Adsorptive Voltammetric Behaviors of Resveratrol at Graphite Electrode and its Determination in Tablet Dosage Form

The adsorptive voltammetric behavior of resveratrol was studied at a graphite electrode in B‐R buffer (pH = 6.0) solution using adsorptive cyclic voltammetric technique. The oxidation of resveratrol is an irreversible adsorption controlled process. The oxidation mechanism was proposed and discussed in this work. The dependence of the current on pH and the concentration and nature of buffer were investigated to optimize the experimental conditions for the determination of resveratrol. It was found that in the range of 8.0 × 10^?9 ～ 2.0 × 10^?6 mol/L, the currents measured by differential pulse voltammetries presented a good linear property as a function of the concentrations of resveratrol. In addition, validation parameters, such as reproducibility, sensitivity and recovery were evaluated as well. The proposed method was also successfully applied for the determination of resveratrol in Chinese patent medicine with good results.     

Determination of trace amounts of estriol and estradiol by adsorptive cathodic stripping voltammetry.

Estriol and estradiol are electroinactive in the potential range from -200 to -1000 mV versus a silver-silver chloride electrode at a mercury electrode. The conversion of these estrogens into electroactive nitro derivatives of estrogens, which are used for voltammetric determination, was studied. Such nitro derivatives give a well defined cathodic stripping wave at -600 mV in pH 10.5 borate buffer. Estriol and estradiol are determined in the ranges 1 x 10(-9)-1.5 x 10(-6) and 5 x 10(-9)-2 x 10(-6) mol dm-3, respectively, by differential-pulse adsorptive stripping voltammetry at a hanging mercury drop electrode. Some steroids, such as estrone, interfere because the three estrogens have almost the same molecular structure and have similar nitro derivatives, but progesterone does not interfere and is reduced at significantly more negative potentials than the nitrated estrogens. It can be determined simultaneously with estriol or estradiol. A method was developed for the assay of estriol in pharmaceutical preparations.     

Adsorptive stripping voltammetric assay of phenazopyridine hydrochloride in biological fluids and pharmaceutical preparations

A sensitive method for the measurement of phenazopyridine hydrochloride (PAP) by differential pulse polarography (DPP) based on adsorptive stripping technique, using a hanging mercury drop electrode (HMDE) is described. The voltammetric peak is obtained at -0.760 V, which corresponds to the reduction of the azo group in Britton-Robinson buffer. The redox behaviour is reversible. Optimum conditions were found to be: accumulation potential -50 mV (vs. Ag/AgCl), accumulation time 60 s, scan rate 5 mV s(-1), pulse amplitude -100 mV and supporting electrolyte Britton-Robinson buffer (0.04 M, pH=11). The relative standard deviation (at 20 ng ml(-1) level) was +/-0.6% for six measurements. The calculated detection limit was 0.0299 ng ml(-1) with a 60-s accumulation time. The applicability of such a method was evaluated through the assay of PAP in human plasma and urine samples after a simple extraction procedure and in pharmaceutical preparation. The mean recovery was 97+/-2 (100 ng ml(-1) plasma).     

Electrocapillary Activity and Adsorptive Accumulation of U(VI)‐Cupferron and U(VI)‐Chloranilic Acid Complexes on Mercury Electrode

Interfacial activity of uranium(VI)‐cupferron and uranium(VI)‐chloranilic acid (CAA) complexes (in 0.1 M acetate buffer pH 4.6 or 0.1 M NaClO₄ respectively) on polarized mercury electrode at 110 mV, 10 mV or ?240 mV respectively vs. saturated calomel electrode (SCE), and under conditions of the application of adsorptive stripping voltammetric techniques was studied. It revealed a competitive effect of interfacial activity of the mentioned complexes consisting in a nonmonotonous effect of the bulk concentration of U(VI) on the adsorption of the mentioned complexing reagents at their constant concentrations. At concentrations lower than 5×10^?5 mol L^?1 the complexes U(VI)‐cupferron or U(VI)‐CAA exhibited a relatively strong electrosorption providing the adsorption coefficients β of the order 10⁴ L mol^?1, the maximum surface excess Γ_m ≈ 5 to 10 μmol m^?2 and average Frumkin interaction coefficients reaching their absolute values 2 to 2.6.     

Adsorptive stripping voltammetry of Tartrazine at the hanging mercury drop electrode in soft drinks

Adsorptive stripping voltammetry was used for the determination of trace amounts of the dye Tartrazine (E-102) by square-wave (SWS) and differential pulse techniques (DPS). Its adsorptive voltammetric behaviour was investigated at different pH media. NH₄Cl/NH₃ buffer solution was chosen as the most suitable, taking into account the sensitivity and definition of the reduction peaks obtained. The effects of the experimental parameters on the determination are discussed. Standard deviations of 3.3% and 2.6% were obtained by SWS and DPS for 100 and 50 μg/L Tartrazine solutions, respectively (n = 10). Both methods were applied to determine the dye in several commercial soft drinks, containing very small amounts of it. Measurements were made directly in the commercial samples. A comparison of the results obtained by the proposed voltammetric methods with those of an HPLC method was also made. Good correlations between the voltammetric results and the values supplied by the manufacturer were found, whereas recoveries of the same order of magnitude were obtained by the HPLC method. Received: 23 May 1996 / Revised: 5 July 1996 / Accepted: 10 July 1996     

Sensitive adsorptive stripping voltammetric method for direct determination of trace concentration of lead in the presence of cupferron in natural water samples

This paper reports the use of an adsorptive voltammetric technique for Pb(II) determination using cupferron as a selective complexing agent. After accumulation of the complex onto a hanging mercury drop electrode, the electrode potential was scanned with differential pulse modulation and the reduction current of lead was observed at about??0.5?V. Under optimum conditions (5?×?10^?4?mol?L^?1 cupferron concentration, 0.1?mol?L^?1 acetate buffer (pH 5.5), adsorption at??50?mV for 30?s) the detection limit was 5.1?×?10^?10?mol?L^?1. The relative standard deviation of five measurements for low lead concentration was 3.1%. The accuracy of the method was tested by analysing certified reference material (SPS-WW1 Waste Water). Finally, the method was successfully applied to the determination of Pb(II) in river water samples without any pretreatments.     

活性艳红K-2G与环糊精相互作用的极谱伏安法研究

研究了单偶氮染料活性艳红K-2G的极谱伏安行为。实验表明：在底液为0．1mol／L的NaGl溶液中活性艳红K-2G有一稳定的、灵敏的还原峰,峰电位约为-0．78mV（vs．SEE）。用线性扫描二阶导数极谱法研究了活性艳红K-2G与不同环糊精的相互作用。采用“电流法”测定了包结常数,比较了不同类型环糊精的包结能力,初探了包结点的可能位置,并对其进行了理论分析。     

Determination of Trace Vanadium by Adsorptive Stripping Voltammetry at a Carbon Paste Electrode

A method for the voltammetric determination of vanadium using a carbon paste electrode (CPE) was described. The new procedure is based on the adsorptive accumulation of the V(V)‐alizarin red S(ARS) complex onto the surface of the CPE, followed by the electrochemical reduction of adsorbed species. The optimal experimental conditions include the use of 0.10 mol/L acetate buffer (pH 5.1), 1.0×10^?5 mol/L ARS, an accumulation potential of ?0.10 V (versus SCE), an accumulation time of 2 min, a scan rate of 200 mV/s and a second‐order derivative linear scan mode. The reduction peak for the complex appears at ?0.52 V. The peak current is proportional to the concentration of V(V) over the range of 0.10–15.0 μg/L, and the detection limit is 0.04 μg/L for a 2 min adsorption time. The relative standard deviations(n=8) for 2.0 and 0.50 μg/L V(V) are 3.1 and 4.7%, respectively. The proposed method was applied to the determination of vanadium in water 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。