Adsorptive stripping voltammetric determination of ofloxacin

The fluoroquinolone antibacterial agent ofloxacin was studied by adsorptive stripping voltammetry. Controlled interfecial accumulation of ofloxacin on a static mercury drop electrode in the hanging mercury drop mode provides high sensitivity. The linear concentration range was 0.079–197.5 μg ml^?1 when using a 60-s preconcentration at ?1 V vs. Ag/AgCl in Britton-Robinson buffer of pH 6.00. The detection limit of ofloxacin was 1 ng ml^?1. The precision is excellent with a relative standard deviation of ca. 0.75% at a concentration of 0.848 μg ml^?1.     

Adsorptive stripping voltammetric determination of antimony

A new method is described for the determination of antimony based on the cathodic adsorptive stripping of Sb(III) complexed with 2′,3,4′,5,7-pentahydroxyflavone(morin) at a static mercury drop electrode (SMDE). The reduction current of the adsorbed antimony complex was measured by 1.5th-order derivative linear-sweep adsorption voltammetry. The peak potential is at −0.51 V (vs. SCE). The effects of various parameters on the response are discussed. The optimized analytical conditions were found to be: supporting electrolyte, chloroacetic acid (0.04 mol/l, pH 2.3); concentration of morin, 5×10⁻⁶ mol/l; accumulation potential, −0.25 V (vs. SCE); scan rate, 100 mV/s. The limit of detection and the linear range were 7×10⁻¹⁰ mol/l and 1.0×10⁻⁹3.0×10⁻⁷ mol/l Sb(III) for a 2-min accumulation time, respectively. This method has been applied to the determination of Sb(III) in steel and brass samples and satisfactory results were obtained. The adsorptive voltammetric characteristics and composition of the Sb(III)–morin complex were studied.     

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.     

吸附转移溶出伏安法测定氟罗沙星注射液含量

氟罗沙星 (ｆｌｅｒｏｘａｃｉｎ ,ＦＬＲＸ)是一种抗菌谱广 ,杀菌力强的三氟喹诺酮类抗菌药[1] 。ＦＬＲＸ含量的测定方式主要有ＨＰＬＣ法[2 ,3] 、紫外分光光度法[3,4 ] 和荧光分光光度法[5] 。本文研究ＦＬＲＸ在不同支持电解质中的电化学行为 ,发现其在石墨电极表面有很强的吸附性 ,在一定的电位下富集几分钟 ,电极冲洗后在底液中扫描 ,仍有很大的峰电流。在此基础上建立了吸附转移溶出伏安法(ＡｄＴＳＶ) [6 ] 测定ＦＬＲＸ。方法的线性范围为 4～42 μｇ/ｍｌ,用于ＦＬＲＸ葡萄糖注射液中ＦＬＲＸ含量的测定 ,比其他方法灵敏、准确、…     

Adsorptive stripping voltammetric determination of chromium in gallium

The electroanalytical chemistry of trace metals has progressed strongly with the development of cathodic stripping voltammetry (CSV) preceded by adsorption collection of organic metal complexes. A sensitive method for the determination of trace amount of chromium in gallium is described. Gallium is dissolved in sodium hydroxide containing hydrogen peroxide. The method is based on the catalytic activity of nitrate ions on the reduction of Cr(III)TTHA (triethylene tetramine-N,N,N',N',N',N'-hexaacetic acid) complex. The sensitivity of this method is further improved by adsorption preconcentration of Cr(III)TTHA complex at a hanging mercury drop electrode (HMDE). The Cr(III) formed at the electrode surface by the reduction of Cr(VI), which is present in the bulk solution, is immediately complexed by TTHA. The adsorbed complex is then reduced at a peak potential of - 1.26 V, and the peak height of Cr(III) reduction is measured. The determination limit was restricted by the amount of chromium present in the reagent blank solution. The method is suitable for the determination of chromium at level as low as 0.2 mug g(-1) (with about 50 mg of sample) and a relative standard deviation of 15%.     

Adsorptive stripping voltammetric determination of ketoconazole in pharmaceutical preparations and urine using carbon paste electrodes

The oxidation of ketoconazole on a bare carbon paste electrode was studied voltammetrically. The results indicated that the process is irreversible and controlled by an adsorption-extraction process which allows the accumulation of the drug at the electrode surface. After the optimization of solution pH, accumulation variables and instrumental parameters, sensitive differential pulse and linear sweep voltammetric peaks were obtained whose peak currents were linearly proportional to the ketoconazole concentration over the ranges 2.4 x 10(-8)-4.8 x 10(-7) and 9.1 x 10(-7)-1.0 x 10(-5) M, respectively. Based on these findings, a simple procedure was developed for the determination of ketoconazole in human urine and formulations.     

Adsorptive stripping voltammetric determination of thiourea and thiourea derivatives

Adsorptive stripping voltammetry of thiourea, α-naphthylthiourea and diphenyl-thiourea is discussed. In perchlorate solution, these compounds are adsorbed at the hanging mercury drop electrode at positive potentials (or at open circuit) and can be stripped in a cathodic scan. Detection limits are 2.5 ng l^?1 for thiourea, 80 ng l^?1 for α-naphthylthiourea and 50 ng l^?4 for diphenylthiourea. The method is applicable in the determination of thiourea in cattle-feed and in the direct analysis of urine.     

Cathodic adsorptive stripping voltammetric determination of nalidixic acid in pharmaceuticals, human urine and serum

The quinolone antibacterial agent nalidixic acid (NAL) was studied by cyclic voltammetry (CV) and cathodic adsorptive stripping voltammetry (CASV). A sensitive method is described for the determination of NAL in its pure form, dosage forms and biological fluids. Controlled adsorptive accumulation of NAL on a hanging mercury drop electrode provides the basis for the direct stripping measurement of that compound in the nanomolar concentration level. Different variables were studied and optimized. The proposed method depends upon the voltammetric activity of NAL in Britton-Robinson buffer, whereby a well-defined cathodic peak is produced at pH 5.0 in presence of NO(3)(-). The calibration graph to determine NAL was linear in the range 7.4x10(-8)-2.5x10(-5) M by CASV. CAS voltammetry has been proved to be advantageous over a liquid chromatographic (LC) technique, allowing to detection limit signal to noise ratio, (s/n=3) of 0.766 ng ml(-1) (3.3x10(-9) M) NAL to be reached. The relative standard deviation (n=5) was 5.2% at concentration level of 1.0x10(-7) M NAL. The degree of interference from coexisting metal ions on the CASV signal for NAL was evaluated. The method was applied to two different commercial pharmaceutical products (Negram tablets and suspension) with very good recoveries. It was also shown that the method was successfully applied to the determination of NAL in human urine and blood serum. Mean recoveries were 98.8+/-0.3 and 98.9+/-0.41%, respectively.     

Cathodic stripping voltammetry of pipemidic acid and ofloxacin in pharmaceutical dosages and human urine

Sensitive cathodic stripping voltammetric methods have been developed for two quinolone antibacterial drugs, pipemidic acid (PIP) and ofloxacin (OFL) using hanging mercury drop electrode as working electrode vs. Ag/AgCl reference electrode. The methods were developed for the determination of drugs individually as well as simultaneously. 0.1 M and 0.01 M hydrochloric acid was used as medium for PIP and OFL, respectively, 0.1 M potassium chloride was used as base electrolyte. Reduction waves were observed for PIP within ?700 mV to ?800 mV and for OFL within ?1100 mV to ?1200 mV. Linear calibration ranges for PIP and OFL were observed within 10–100 μg ml^?1 with detection limits of 50 ng ml^?1 and 1 μg ml^?1, respectively. Relative standard deviations (RSD) for the analysis of 10 gµg ml^?1 of PIP and OFL (n = 6) were 0.5% and 1.4%, respectively. The presence of glucose, lactose, sorbitol, gum arabic, starch, magnesium stearate, methylparaben and propylparaben did not affect the determinations of both PIP and OFL. The methods were used for the analysis of pharmaceutical preparations and the results indicated relative deviation of 0.5–5.5% from labeled values with RSD within 0.49–2.5%. PIP and OFL could also be determined simultaneously, and were determined from spiked human urine.     

Adsorptive stripping voltammetric determination of netilmicin in the presence of formaldehyde

A linear sweep adsorptive stripping voltammetric method for the determination of netilmicin in the presence of formaldehyde has been proposed for the first time. In the presence of 3.0×10⁻³ g ml⁻¹ formaldehyde, netilmicin exhibits a sensitive cathodic peak at −1.30 V (vs. the saturated calomel electrode, SCE) in a medium of Britton–Robinson buffer (pH 8.7) with a scan rate of 100 mV s⁻¹ after a preconcentration period of 120 s at −1.10 V (vs. SCE). The peak current showed a linear dependence on the netilmicin concentration over the range 4.2×10⁻⁹–1.0×10⁻⁷ g ml⁻¹. The achieved limits of detection and quantitation were 1.0×10⁻¹⁰ and 3.3×10⁻¹⁰ g ml⁻¹ netilmicin, respectively. It was deduced from the experiments that the amine–aldehyde condensation product formed between netilmicin and formaldehyde is mainly responsible for the appearance of the peak. The electrochemical behavior of netilmicin in the presence of formaldehyde has been studied. The method was applied to the direct determination of netilmicin in injectable formulations and spiked human urine and serum samples.      

Adsorptive stripping voltammetric determination of the anti-inflammatory drug celecoxib in pharmaceutical formulation and human serum

Celecoxib is a cyclooxygenase inhibitor, that has been recently and intensively prescribed as an anti-inflammatory drug in rheumatic osteoarthiritis. A robust, highly reliable and reproducible square-wave (SW) adsorptive cathodic stripping voltammetric procedure was developed for the determination of celecoxib in pharmaceutical formulation and human serum. The analytical procedure was based on the reduction of the CN of the pyrazole ring of the drug molecule at the mercury electrode surface in Britton-Robinson buffer of pH 7.0. The SW adsorptive cathodic stripping voltammogram of celecoxib showed a single well-defined peak at −1.54 V (vs. Ag/AgCl/KCl_s) using an accumulation potential of −0.70 V, frequency of 120 Hz, scan increment of 10 mV and pulse amplitude of 25 mV. Repeatability was examined for 1×10⁻⁸ M CXB drug solution after 30 s pre-concentration and a mean recovery of 99.4±0.4% (n=5) was achieved. For 90 s preconcentration, a linear concentration range of 1×10⁻⁹-2×10⁻⁸ M CXB and a detection limit of 1.86×10⁻¹⁰ M were achieved. The proposed procedure was successfully applied for the determination of the drug in capsules and human serum with mean recoveries of 101.5±0.6 and 98.8±1.1%, respectively. A detection and quantitation limits of 1.0×10⁻⁹ M (0.4 ng ml⁻¹) and 4.7×10⁻⁹ M (1.3 ng ml⁻¹) were achieved for the determination of the drug in human serum. Moreover, the procedure was useful for study of the pharmacokinetic profile of celecoxib in a healthy volunteer after administration of a single oral dose (celebrex®, 200 mg).     

Adsorptive stripping voltammetric determination of cobalt at ppb levels in high-purity aluminium

Summary A sensitive procedure for the determination of cobalt in high-purity aluminium using DPCSV through adsorptive accumulation of Co(DMG)₂ on HMDE in triethanolamine + NH₄OH buffer is described. Analysis of NBS SRM C-1257 and a reactor grade aluminium sample is reported. Prior to the determination, cobalt was separated from Al and Ni on AG-1 X8 resin in 9 mol/l HCl. The results have been cross-validated by INAA.     

Square wave adsorptive stripping voltammetric determination of famotidine in urine

Electrochemical studies of famotidine were carried out using voltammetric techniques: cyclic voltammetry, linear sweep and square wave adsorptive stripping voltammetry. The dependence of the current on pH, buffer concentration, nature of the buffer, and scan rate was investigated. The best results for the determination of famotidine were obtained in MOPS buffer solution at pH 6.7. This electroanalytical procedure enabled to determine famotidine in the concentration range 1 × 10⁻⁹–4 × 10⁻⁸ mol L⁻¹ by linear sweep adsorptive stripping voltammetry (LS AdSV) and 5 × 10⁻¹⁰–6 × 10⁻⁸ mol L⁻¹ by square wave adsorptive stripping voltammetry (SW AdSV). Repeatability, precision and accuracy of the developed methods were checked. The detection and quantification limits were found to be 1.8 × 10⁻¹⁰ and 6.2 × 10⁻¹⁰ mol L⁻¹ for LS AdSV and 4.9 × 10⁻¹¹ and 1.6 × 10⁻¹⁰ mol L⁻¹ for SW AdSV, respectively. The method was applied for the determination of famotidine in urine.     

Adsorptive stripping square-wave voltammetric behavior of rofecoxib

Adsorption and reduction of rofecoxib were investigated by cyclic and square-wave voltammetry on a hanging mercury drop electrode in electrolytes of various pH values. The reduction process on hanging mercury drop electrodes gave rise to a single peak within the entire pH range (2.0-11.5). In alkaline solutions, rofecoxib gave a sensitive adsorptive reductive peak; approximately 10 times larger than those obtained by applying a square-wave scan without prior accumulation. Application of the method to the determination of rofecoxib in two pharmaceutical products (Vioxx 12.5 and 25 mg), without sample pretreatment, resulted in acceptable deviation from the stated concentrations.     

Adsorptive stripping square-wave voltammetric behavior of insulin

The adsorptive stripping voltammetric behavior of bovine insulin has been studied by both differential pulse and square-wave techniques, leading to analytical methodologies for its determination in aqueous samples and pharmaceutical preparations. The application of a square-wave mode for the stripping of adsorbed bovine insulin has proved to be much more sensitive, yielding signals 20 times larger than those obtained by applying a differential pulse scan. The precision obtained for the voltammetric method, at a concentration level as low as 0.77 mg L^–1 of the protein, was found to be 1.45% (RSD., n = 8) by SWS and 2.20% (RSD., n = 8) by DPS. The pharmaceutical product Actrapid containing biosynthetic human insulin was analyzed by both methods. Received: 25 February 1999 / Revised: 6 April 1999 / Accepted: 12 April 1999     

Adsorptive stripping voltammetric determination of dimenhydrinate at a hanging mercury drop electrode

Dimenhydrinate exhibits a single adsorptive stripping peak at a hanging mercury drop electrode after accumulation at 0.0V vs Ag/AgCl electrode at pH 3.8 (acetate buffer). The addition of trace amounts of copper ions enhanced the dimenhydrinate peak and its height depends on the concentration of each dimenhydrinate and Cu²⁺. The adsorptive stripping response was evaluated with respect to accumulation time and potential, concentration dependence, electrolyte, the presence of other purines, surfactants and other metal ions, and some variables. The calibration graph for dimenhydrinate determination is linear over the range 2.0×10^–8–2.0×10^–7 M (pre-concentration for 60s). The correlation factor is found to be 0.985 and RSD is 3.2% at 1.0×10^–7 M. Detection limit is 1.0×10^–8 M after 5 min accumulation. The determination of dimenhydrinate in pharmaceutical formulations by the proposed method is also reported.     

Adsorptive stripping square-wave voltammetric behavior of insulin

The adsorptive stripping voltammetric behavior of bovine insulin has been studied by both differential pulse and square-wave techniques, leading to analytical methodologies for its determination in aqueous samples and pharmaceutical preparations. The application of a square-wave mode for the stripping of adsorbed bovine insulin has proved to be much more sensitive, yielding signals 20 times larger than those obtained by applying a differential pulse scan. The precision obtained for the voltammetric method, at a concentration level as low as 0.77 mg L^–1 of the protein, was found to be 1.45% (RSD., n = 8) by SWS and 2.20% (RSD., n = 8) by DPS. The pharmaceutical product Actrapid containing biosynthetic human insulin was analyzed by both methods. Received: 25 February 1999 / Revised: 6 April 1999 / Accepted: 12 April 1999     

Adsorptive stripping voltammetric determination of midazolam as a method for quality control

Controlled interfacial accumulation of the benzodiazepine midazolam at a hanging mercury drop electrode provides the basis for a highly sensitive and accurate adsorptive stripping voltammetric procedure. The response was linear in the range 1.9 × 10^?6? × 10^?9 M when using a 120-s preconcentration at ?0.45 V vs. Ag/AgCl in Britton-Robinson buffer of pH 5.00. In this range the relative standard deviation was between 1.21 and 1.62%. The applicability of the method to pharmaceutical preparations is discussed.     

Adsorptive stripping voltammetric determination of cobalt in the presence of dimethylglyoxime and cetyltrimethylammonium bromide

A sensitive procedure for determination of micro-traces of Co(II) by adsorptive stripping voltammetry is proposed. The procedure exploits the enhancement of the cobalt peak obtained by use of the system Co(II)–dimethylglyoxime–piperazine-1,4-bis(2-ethanesulfonic acid)–cetyltrimethylammonium bromide. Using the optimized conditions, a detection limit (based on the 3 criterion) for Co(II) of 1.2×10^–11 mol L^–1 (0.7 ng L^–1) was achieved. The calibration plot for an accumulation time of 30 s was linear from 5×10^–11 to 4×10^–9 mol L^–1. The procedure was validated by analysis of certified reference materials and natural water samples.     

Adsorptive stripping voltammetric determination of the anti-inflammatory drug tolmetin in bulk form, pharmaceutical formulation and human serum

The electro-reduction of tolmetin at the hanging mercury drop electrode was studied in different supporting electrolytes using cyclic voltammetry and square-wave stripping voltammetry techniques. Voltammograms of tolmetin exhibited a single well-defined 2-electron irreversible cathodic peak in media of pH < 4, which may be attributed to reduction of the >C=O double bond of the analyte molecule. Adsorption of tolmetin onto the surface of the hanging mercury electrode was identified and each adsorbed tolmetin molecule was found to occupy an area of 0.23 nm². A square-wave adsorptive cathodic stripping voltammetric procedure was described for the direct determination of tolmetin in bulk form and pharmaceutical formulation (Rumatol® capsules) with a limit of quantitation of 2 × 10^?9 M and a mean percentage recovery of 98.35 ± 1.21% to 99.57 ± 1.23. Moreover, the described procedure was successfully applied for the direct assay of tolmetin in spiked human serum without pretreatment or extraction prior to the analysis while a quantitation limit of 5 × 10^?9 M tolmetin was achieved.