Voltammetric study of ketorolac and its differential pulse polarographic determination in pharmaceuticals

A differential pulse polarographic method for the quantitative determination of ketorolac is described. Ketorolac is an antiinflamatory-analgesic agent that is directly electroreducible at the mercury electrode. The polarographic reduction is due to the reduction of the benzoyl moiety in the ketorolac molecule. For analytical purposes, a very well resolved diffusion controlled differential pulse polarographic peak obtained at pH 9 was selected. This peak was used to develop a new method for the determination of ketorolac in pharmaceutical dosage forms. Recovery study shows that the method is sufficiently accurate and precise to be applied in the individual tablet assay of commercial samples.     

The differential pulse polarographic determination of chromium in gallium arsenide

The method described for the determination of chromium in gallium arsenide is based on the catalytic current produced by nitrate in the electrolytic reduction of the chromium(VI)-diethylenetriaminepentaacetate complex. Matrix effects, primarily caused by gallium, are discussed in detail. The method is suitable for determinations of chromium at levels as low as about 1 μg g^?1 with about 50 mg of sample; the r.s.d. is better than 10%.     

The differential pulse polarographic determination of trace amounts of tin and its application to zinc-aluminium alloys

A differential pulse polarographic procedure for the determination of 0.001-0.02% of tin in zinc-aluminium alloys is described. The tin is first separated from interfering elements such as copper and lead by homogeneous co-precipitation with aluminium succinate. The tin is determined polarographically in a 1M hydrochloric acid + 4M ammonium chloride electrolyte. After the tin has been masked with alkaline citrate a second polarogram is recorded to ascertain whether residual lead is present and, if so, a correction is applied.     

Voltammetric behavior of naratriptan and its determination in tablets

The electrochemical behavior and the analytical application of the selective serotonin agonist naratriptan (N-methyl-3-(1-methyl-4-piperidyl)indole-5-ethanesulfonamide) are presented herein. Naratriptan exhibits an anodic response in aqueous media over a broad pH range (pH 2-12), as determined by differential pulse voltammetry and cyclic voltammetry using glassy carbon electrodes. This response is irreversible in nature, diffusion-controlled and probably caused by the oxidation of the naratriptan indole moiety. The differential pulse voltammetry technique was performed in 0.1 mol L⁻¹ Britton-Robinson buffer (pH = 3), which elicited the most reproducible results. The percentage of naratriptan recovery was 102.1 ± 1.8%, and the limits of detection and quantitation were 9.5 × 10⁻⁶ and 2.0 × 10⁻⁵ mol L⁻¹, respectively. Selectivity trials revealed that the oxidation signal of the drug was not disturbed by the presence of excipients or degradation products. Thus, we conclude that the method presented herein is useful for the quantification of naratriptan in pharmaceutical drugs and that this method requires no separations or extractions. Finally, this voltammetric method was successfully applied to determine the quantity and the content uniformity of naratriptan in drug tablets. A comparison of this technique to the standard high-performance liquid chromatography technique was conducted at the end of our study.     

Differential pulse polarographic determination of salicylaldehyde as its Girard-P derivative

A method for the determination of salicylaldehyde (2 × 10^–6–10^–4 M) by differential-pulse polarography, based on the in situ formation of its Girard-P derivative in aqueous solution at pH 2.5, is proposed. The relative standard deviation was 1.5% (ten determinations of 4 × 10^–5 M level). The applicability of this method was checked in synthetic samples containing salicyl alcohol,o-aminophenol, 2-methylphenol, salicylic acid and 4-aminobenzoic acid.     

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.     

Differential pulse polarographic determination of cyanuric chloride

Cyanuric chloride (2,4,6-trichloro-1,3,5-triazine) can be determined by fastscan differential pulse polarography in methanolic acetate buffer solution at pH 5.6 at a hanging mercury drop electrode. At positive potentials, the insoluble salt formed between cyanuric chloride and mercury(I) is adsorbed on the mercury surface and the d.p.p. current is enhanced. The detection limit is 0.2gmg ml^?1. Cyanuric chloride in air can be determined after absorption in methanol.     

Differential pulse polarographic determination of sulfuric acid

Acetonitrile is used as a solvent for the determination of micromolar amounts of sulfuric acid by differential pulse polarography. Contaminants in the supporting electrolyte and solvent present the biggest problems to the accurate determination of sulfuric acid. The detection limit is 2 × 10^-7 M. Nitric acid. bromide, soluble sulfates, and ammonium hydrogensulfate interfere under certain conditions.     

乙醛酸的微分脉冲极谱法定量分析

建立了乙醛酸的微分脉冲极谱定量分析方法, 乙醛酸在100 g/L KOH底液中, 于-1.35 V (vs. Ag/AgCl)处出现一良好的微分脉冲极谱峰, 并能排除主要杂质草酸的干扰. 乙醛酸浓度与其电流峰幅值呈显著的线性关系, 当标准加入的极谱电流峰高和样品极谱电流峰基本一致时, 测量误差小于0.5%.     

Electrochemical behavior of atomoxetine and its voltammetric determination in capsules

In this work, the electrochemical behavior and the analytical application of atomoxetine, a selective noradrenaline reuptake inhibitor, are studied. Atomoxetine, studied by differential pulse voltammetry and cyclic voltammetry on a glassy carbon electrode, exhibited an anodic response in aqueous media with pH between 1.5 and 7. In non-aqueous medium (acetonitrile), the drug exhibited two irreversible oxidation peaks that are diffusion controlled. From chronocoulometric studies in acetonitrile, it was determined that each oxidation signal involves two and four electrons, respectively. For analytical purposes, a differential pulse voltammetry technique in 0.1 mol L⁻¹ perchloric acid was selected, which exhibited adequate figures of merit. The percent recovery was 96.6 ± 1.2 and the detection and quantitation limits were 6.9 × 10⁻⁵ and 1.0 × 10⁻⁴ mol L⁻¹, respectively. Also, results indicate that excipients do not interfere with the oxidation signal of atomoxetine, which leads to the conclusion that the developed method is satisfactorily selective for atomoxetine quantification in pharmaceuticals with no prior separation or extraction necessary. Finally, the proposed voltammetric method was successfully applied to both the assay and the uniformity content of atomoxetine in capsules. For comparison, high-performance liquid chromatography analysis was also performed.     

Assessment of a new method for the differential pulse polarographic determination of silicon in steel

A procedure is described by which silicon in steel may be determined by differential pulse polarography after removal of iron. Silicomolybdic acid is formed within 20 min by reaction of the silicon with molybdate in the presence of methyl ethyl ketone: subsequent addition of citrate buffer prevents interference from phosphate and excess of molybdate. At the levels present in high-purity iron ( approximately 0.002%) the precision for silicon is better than that usually quoted for the molybdenum blue method. The steel is dissolved by standard procedures but iron must be removed before the silicon is determined. The lower limit imposed by the polarography is about 10(-5)% silicon, but the practical lower limit is probably set by the difficulty of removing the last traces of iron.     

Voltammetric behavior of methaqualone and its determination by single-sweep oscillopolarography

A well derivative reduction wave of methaqualonc (MTQ) was obtained in 0.033 mol dm⁻³ B-R (pH 3.76) buffer solution by single-sweep oscillopolarography. The peak potential is −1.36 V (vs. saturated calomel reference electrode, SCE). The peak current is proportional to the concentration of methaqualone over the range of 7.0×10⁻⁸-9.0×10⁻⁶ mol dm⁻³. The method has been successfully applied to the determination of methaqualone in tablets. The wave is believed to result from irreversible adsorption through studies of its electrochemical behavior and reaction mechanism.     

The polarographic behavior and determination of glafenine

Glafenine was found to be reducible at the dropping-mercury electrode (DME) in Britton-Robinson buffer (BRB) over the whole pH range. In the alkaline range, a well-defined cathodic wave was produced. The wave was characterized as being diffusion-controlled and partially affected by adsorption phenomena. A method was proposed for the determination of glafenine in tablets and the results obtained were satisfactorily accurate and reproducible.     

The application of 2,4,6-trinitrobenzene-1-sulphonic acid in the differential pulse polarographic determination of amines

The differential pulse polarographic behaviour of 2,4,6-trinitrophenyl (TNP) derivatives of several primary amines and amino acids was investigated in the presence of sulphite ion. All the derivatives produced a polarographic peak for their complexes with sulphite (1 × 10^?2 M) in pH 8.0 phosphate buffer (0.05 M)/0.1 M potassium chloride. The derivatives of proteins and peptides did not give such a peak. A 5-min reaction time at room temperature (or 50°C for lysine) and pH 10.5 using 1 × 10^?4 M 2,4,6-trinitrobenzene-1-sulphonic acid provides the optimal conditions for the determination of 5 × 10^?6?2.5 × 10^?5 M amines. The relative standard deviation for determining 1 × 10^?5 M glycine (n = 5) was 1%.     

Differential pulse polarographic determination of procymidone in formulations and wine

The dicarboximide fungicide procymidone was studied systematically by using direct current polarography, cyclic voltammetry, differential pulse polarography (DPP), controlled potential electrolysis, and millicoulometry in the universal buffer medium with dimethylformamide as the solvent. Procymidone exhibited a single well-defined polarographic wave in the pH range 2.0-6.0, leading to the formation of the hydroxy compound. The overall reduction process was diffusion-controlled and adsorption-free. The variation of half-wave potential with pH, the concentration of the analyte, and other experimental conditions are described. The reduction mechanism proposed is an overall 4-electron process, in which the dicarboximide group is reduced. DPP was used to determine procymidone in agricultural formulations and wine at the optimum conditions found; a detection limit of 2.4 x 10(-9) M was estimated. The results obtained by the proposed method were also compared with those obtained by other methods.     

A new simple sensitive differential pulse polarographic method for the determination of acrylamide in aqueous solution

A new simple sensitive differential pulse polarographic (DPP) method was investigated for the determination of acrylamide (AA) directly in a neutral aqueous solution. The AA showed a well-defined and well-resolved peak in pure aqueous LiCl at −1.84 V in the potential range from −1.6 V to −1.97 V at nitrogen pressure of 0.5 kg cm⁻². Among the various electrolytes studied, the AA showed good DPP response in the presence of LiCl and tetra methyl ammonium iodide, while it showed poor response in the presence of tetra butyl ammonium hydroxide and tetra butyl ammonium bromide due to their strong adsorption on the surface of electrode which hindered its reduction. The effect of LiCl concentration, the cyclic voltammetric response and the drop time study showed that AA exhibited an irreversible adsorptive electrochemical behavior. The good electrochemical response in pure aqueous medium suggested that hydrogen bonding might be involved which may favor the electrode reaction. Under optimized conditions, the peak current was linear in the entire concentration range from 0.2 mg L⁻¹ to 20 mg L⁻¹ with the correlation coefficient of R² = 0.9998. The method showed good reproducible results with R.S.D. of 0.3% (n = 16). The detection limit (LOD) was 27 μg L⁻¹. The influence of various interfering agents was also studied. The method was applied successfully for the quantification of AA in water samples without any interference effect from alkali metals.     

Differential pulse polarographic determination of orthophosphate in aqueous media

The determination of orthophosphate in aqueous media by differential pulse polarography is described. It is based on determination of the molybdenum in 12-phosphomolybdic acid. High sensitivity is achieved by measuring the polarographic wave due to the catalytic reduction of perchlorate or nitrate in the presence of molybdenum(VI). The method is suitable for samples as small as 3.5 ml which contain as little as 9 ng of phosphorus per ml. The average relative deviation is 3.0% at the 0.045 mg/l. phosphorus level and 1.6% at the 1.2 mg/l. level. Results for the analysis of EPA quality-control water and real surface-water samples are reported.     

Differential pulse polarographic determination of hydrocortisone in pharmaceutical preparations

Differential pulse polarograms of hydrocortisone recorded from acetate buffer pH 4.6 exhibit a well-defined peak at —1.25 V vs. SCE and the peak current is proportional to the concentration in the range 10^-5–8 × 10^-5 M. The electrode reaction involves one electron and one hydrogen ion. A simple rapid method is proposed for the determination of hydrocortisone in creams and ointments. The procedure does not involve time-consuming extractions, but it is not applicable to samples containing surfactants like polyethyleneglycol which are more strongly adsorbed on the electrode than hydrocortisone. Because degradation in the side chain of hydrocortisone is not detected polarographically, the method is suitable for production control but not for stability tests.     

Electrochemical studies and differential pulse polarographic analysis of lansoprazole in pharmaceuticals

The electrochemical reduction of lansoprazole was investigated by cyclic voltammetry and direct current and differential pulse polarography. The reduction potential was -1.32 V vs. Ag/AgCl with a dropping mercury electrode in a supporting electrolyte consisting of phosphate buffer (pH 9.0)-tetramethylammonium iodide (4 + 1). The reversibility of the electrode reaction and the type of limiting current were studied. The temperature coefficient and the diffusion constant were determined. A mechanism for the electrode reaction was proposed. A new simple and sensitive differential pulse polarographic method was also developed for the quantification of lansoprazole. A linear calibration graph was obtained in the range 0.04-11.35 micrograms ml-1. The limit of detection was 0.03 microgram ml-1 and the intra- and inter-day precisions were 0.84-2.32 and 0.72-3.09%, respectively. The developed method was applied to six different commercial pharmaceutical capsule preparations containing enteric-coated granules. The relative standard deviations ranged from 1.36 to 2.85%. Recovery studies for the accuracy of the method were performed by adding a synthetic mixture to known amounts of lansoprazole and the mean recovery was 100.45%. The data obtained from commercial preparations were compared with those from a published spectrophotometric method. No difference was found statistically.