Amperometric and Conductimetric Methods for Simultaneous Determination of Captopril and Bendroflumethiazide

Abstract

The mixture of captopril (antihypertensive) and bendroflumethiazide (diuretic) was assayed using conductimetric and amperometric methods. Each method was applied for the analysis of laboratory-made sample mixtures in authentic and dosage forms. For captopril, the amperometric and conductimetric methods gave mean percent recoveries of 100.2 ± 1.2 and 99.6 ± 1.2, respectively. These results have shown good agreement when compared with other methods in the literature. When applied to bendroflumethiazide the conductimetric method gave percent recovery of 98.5 ± 1.6 which agreed closely with the spectrophotometric pharmacopoeial method.

The pK₁ for captopril was determined potentiometrically at room temperature (25°C) in aqueous medium. The calculated value, based on Henderson equation was 3.78.     

Potentiometric Determination of Acids and Bases using Silicone Rubber Based Graphite Electrode

Abstract

A silicone rubber based graphite electrode has been used as an indicator electrode for potentiometric acid-base titrations. The electrode potential changes an average of 30 mV per pH-unit. If the electrodes are pretreated with a solution of an oxidant before use, the pH-sensitivity is increased. The electrode can be used in both aqueous and non-aqueous solutions. A measuring cell, composed of a silicone rubber based graphite electrode of small surface area and a chloride-selective reference electrode, can be used for acid-base titrations in the micro range.     

FIA titrations of phenothiazine derivatives in aqueous micellar and non-aqueous media

New methods of flow injection analysis (FIA) neutralization titrations of phenothiazine derivatives in aqueous micellar medium of a cationic surfactant using potentiometric and spectrophotometric detection were proposed; titrations with a mixing gradient chamber and high-speed titrations were compared. The FIA titration method in non-aqueous media based on an official method of determination (titration with perchloric acid in anhydrous acetic acid) was also developed. Under optimized reaction conditions and flow-through parameters, the calibration range and equations, the sensitivity, and the repeatability of all methods were found and discussed. All titrations were assayed for medicinal forms.     

Use of a NICA-Donnan approach for analysis of proton binding to a lignocellulosic substrate extracted from wheat bran

The acid-base properties of a lignocellulosic substrate extracted from wheat bran have been investigated. The lignocellulosic substrate was first studied by use of FTIR, XPS, and solid-state 13C NMR to characterize the surface-active groups. Major contributions arise from the presence of carboxylic and phenolic sites. The former are associated with long-chain fatty acids and the latter are constituent units of lignin. All ionizable sites were quantified by use of the Ca-acetate method and by potentiometric titrations in non-aqueous media. Results were compared with those from conductimetric titrations in water and in the presence of barium ions. Protometric titration curves for the lignocellulosic substrate were obtained at several ionic strengths. Data were also treated with the NICA-Donnan model to determine the intrinsic ionization parameters.     

Non-aqueous cerimetric determination of dithiocarbamates and its application to the determination of amines

A non-aqueous titrimetric method for determination of dithiocarbamates with cerium(IV), is described. The compounds are titrated at room temperature, with visual and potentiometric end-point detection. In visual titrations, the reagent serves as self-indicator and turns the solution yellow at the end-point. Methyl Red can also be used as the indicator. The method has been applied to the determination of amines after their quantitative conversion into dithiocarbamates by reaction with carbon disulphide. The proposed method is accurate to +/- 0.8% with a relative standard deviation of +/- 0.7%.     

A Simple Sensor for Potentiometric Titrations

Abstract

A sensor for potentiometric titrations was prepared by coating a spectroscopic graphite rod with a solution of poly(vinyl chloride) and dioctylphthalate in tetrahydrofuran. The reference was a Ag/AgCl single-junction electrode. The sensor was used in the following potentiometric titrations:

1. precipitation titrations 2. acid-base titrations, 3. compleximetric titrations, and 4. redox titrations.

A survey of its use in such titrations is presented.

Preparation of the coated-graphite sensor is simple and rapid. Moreover, it is quite inexpensive. A limitation is its applicability in aqueous media only, because organic solvents will dissolve the membrane.     

Determination of dissociation constants for coordination compounds of Cr(III) and Co(III) using potentiometric and spectrophotometric methods

The acid–base properties of analogous complex ions of chromium(III) and cobalt(III) in aqueous solution have been studied. The equilibrium constants for all metal complexes were determined by using potentiometric and spectrophotometric titration methods. First, dissociation constants for the studied complexes of Cr(III) and Co(III) were determined by means of the potentiometric titration method and using the STOICHIO computer programme. Then, pH-spectrophotometric titrations were performed and the OriginPro 7.5 computer programme was used to calculate the same constants. The measurements using both methods were carried out under the same conditions of temperature, T = 298.15 K, and over the same pH range 2.00–10.00, respectively. It turned out that the two methods used enabled us to obtain acidity constants in very good agreement.     

Bromamine-B as a new oxidimetric titrant

A new oxidimetric titrant, bromamine-B (sodium salt of N-bromobenzenesulphonamide) is introduced for use in aqueous medium. Direct potentiometric and visual end-point titrations and back-titration procedures have been developed for the determination of typical reductants.     

Determination of mercaptopyrimidines with copper(II) in acetonitrile

A non-aqueous oxidimetric method is described for the determination of mercaptopyrimidines with copper(II) perchlorate in acetonitrile, diphenylamine being used as indicator. A bright platinum wire is used as indicator electrode and a modified calomel or an antimony electrode as reference for potentiometric titrations. The method, based on the oxidation of the mercapto group to the disulphide, is simple, accurate and reliable.     

交流示波极谱滴定的研究(Ⅻ)——中和滴定

本文系统地报导了交流示波极谱滴定在中和滴定中的应用,解决了弱酸弱碱在水溶液中直接滴定等问题。同时提出了中和滴定的两大类指示剂的概念,并且总结了它们的性质。因此,示波极谱中和滴定将大大地丰富中和滴定的内容,扩大其应用范围。     

Determination of Prifinium Bromide in Six Pharmaceutical Formulations by Reverse-Phase Hplc

Abstract

Prifinium bromide is an anti-cholinergic drug, available commercially in various pharmaceutical formulations such as tablets, suppositories, syrups, and ampoules. The present available analytical methods are time-consuming and range from non-aqueous titration to UV-spectrophotometry to ion-pair visible spectrophotometry. The method reported here is a fast, reliable, and stability-indicating reversed phase HPLC for prifinium bromide in its various pharmaceutical formulations. The mobile phase was 0.03 M ammonium acetate in acetonitrile: water (65:35); the pH was adjusted to 4.0 with glacial acetic acid. The column utilized was (250 mm × 4.6 mm i.d.) Supelcosil LC-8-DB (5μ) and detection was carried at 254 nm. Benzophenone was used as internal standard. The assay was applied to commercial products and the results expressed in (% label claim ± RSD) are (99-58 ± 0.36), (100.50 ± 0.40), (99-95 ± 0.70), (99. 94 ± 0.29), (100.28 ± 0.52), and (99-99 ± 0.57) for six commercial formulations. The method was tested for linearity, recovery, and specificity and was found fast, stability-indicating, and free from interferences. The method can be extended to separate     

Simple Rapid Validated RP-LC Method for the Estimation of Flurbiprofen in Rabbit Serum and Aqueous Humor

Abstract

New reversed-phase liquid chromatographic methods, with UV detection, were developed for the quantitative estimation of flurbiprofen in rabbit blood serum and aqueous humor. The mobile phase and other chromatographic conditions were optimized to minimize interference from biological matrix and at the same time provide sufficient sensitivity for the method to be adopted for in vivo studies of ophthalmic formulations of flurbiprofen. Acetonitrile was used to precipitate proteins from serum or aqueous humor during sample preparation. A mobile phase of methanol: acetonitrile: phosphate buffer pH 5.6 (40:20:40) was employed with UV detection at 248 nm for estimation of drug in both the biological matrix. The retention time and asymmetry factor for the proposed method of estimation in serum and aqueous humor was found to be 3.1312±0.0101 min and 1.1310±0.0091 respectively. The linear regression equations obtained by least square regression method, were Area (µV sec) = 52.27 × Conc. (in ng/ml)–1618.70 in serum and Area (µV sec) = 61.79 × Conc. (in ng/ml) ? 783.24 in aqueous humor. The results of analysis were treated statistically, as per ICH guidelines for validation of analytical procedures, USP-2003, and by recovery studies. The results were found to be accurate, reproducible and free from interference. The developed methods were further used for estimation of flurbiprofen in rabbit serum and aqueous humor following single topical administration of in-house aqueous drop and market formulation to rabbit eye.     

Design of composite films and ultrathin membranes of interpolymer complexes

The formation of stoichiometric interpolymer complexes (IPCs) between the poly(vinyl ether) of ethyleneglycol and the copolymer of acrylic acid–butyl vinyl ether, between copolymers of vinyl ether of ethyleneglycol–butyl vinyl ether, and the copolymer of acrylic acid–vinylbutyl ether is demonstrated by conductimetric, potentiometric, viscometric and spectroturbidimetric methods in aqueous solution. The swelling/deswelling behavior of composite films derived from the IPC has been studied in water, alcohol and water–alcohol mixtures, depending on various factors. The formation of polyelectrolyte complexes (PECs) between the copolymer of acrylic acid–vinyl butyl ether and poly(vinyl ether of monoethanolamine) on a dimeric interface of water–butanol has been studied by the potentiometric method. The kinetics of PEC formation on a dimeric interface was measured and the activation energy of this process was calculated. Copyright © 2000 John Wiley & Sons, Ltd.     

Identification of isothiocyanates (Mustard oils) and liquid primary amines via the formation of 1-substituted 2-tetrazoline-5-thione

The oscillometric method is suggested for the determination of alkali salts of organic acids in non-aqueous media. In the titrations of organic sodium and potassium salts the influence of water content and dielectric constant of non-aqueous solvents on the slopes of the titration curves was investigated. Errors obtained were in the range of±0.6 to 1.5%.     

交流示波极谱滴定的研究(ⅩⅢ)——有机碱及有机酸盐类药物在水溶液中的中和滴定

本文用交流示波极谱中和滴定技术,在水溶液中直接滴定有机碱和有机酸的盐类药物,简便、快速、准确。     

Coordination mode and reactivity of nickel(II) with vitamin B6

This contribution presents a selection of results obtained using spectrophotometric and potentiometric titrations. For several reasons, the investigated equilibria present particular challenges to traditional analysis techniques. Equilibrium constants and UV–vis absorption spectra for different ligands in the complexation process of Ni(II) with pyridoxamine (pm), pyridoxal (pl) and pyridoxine are reported. The gradual and cumulative stability constants occurring in aqueous solution are presented for all complexes studied. Additionally, crystal-field parameters were calculated for two nickel(II) complexes synthesized, [Ni(pm)₂]Cl₂ and [Ni(pl)₂]Cl₂, respectively. The minimum inhibitory concentration and minimal bactericidal/fungicidal concentration values for Ni(II) complexes studied were obtained at 25 °C for 24–48 h. The activity data show that the complexes are more potent antimicrobials than the parent ligands.     

Interactions between oxovanadium (IV), glycylvaline and imidazoles: An aqueous potentiometric and spectroscopic study

Speciation has been determined in aqueous oxovanadium, glycylvaline and imidazoles at 25 ± 1°C and μ = 0.1M NaClO₄ using a combination of potentiometry, and visible and EPR spectroscopy. Results of potentiometric and spectroscopic methods are consistent. Calculations of stability constants have been made using the SCOGS computer program.     

Some equilibrium constants of tellurous acid

The various literature values of the equilibrium constants for the system TeO₃²⁻H⁺ are tabulated, and the wide divergence in the values is noted. Solubility measurements and potentiometric titrations were used to re-evaluate some of the constants. The determinations were made in aqueous solutions, and at a range of ionic strengths (sodium perchlorate). The values found for aqueous solution, with no perchlorate, were as follows: pK_HL^H = 9·56 ± 0·02, pK_H2L^H = 6·08 ± 0·06, pK_H3L^H = 2·8 ± 0·2. There was no evidence of polynuclear species at concentrations below 0·05 M.     

Palladium metal electrode and its analytical application to precipitation and acid–base analysis in aqueous and non-aqueous media

Electrochemical characterization of palladium electrode has been reported. The investigated electrode showed a linear dynamic response for p-toluensulfonic acid and iodide ions in the concentrations range between 5?×?10^?1 and 1?×?10^?5 mol L^?1 with a Nernstian slope of 55 mV for p-toluensulfonic acid and 63 mV per decade for iodide ions in water, as well as 53 mV for p-toluensulfonic acid and 51 mV per decade for iodide ions in dioxane. The response time of the electrodes was less than 10 s in the used solvents. Some potential analytical applications of the sensors have been pointed. Palladium electrode for the potentiometric titrations of acids (citric, barbituric, and p-toluensulfonic acid), bases (N,N’-diphenylguanidine, tributylamine, and 2,2'–bipyridine), halides, and some real samples in aqueous and non-aqueous solutions were studied. Тetrabutylammonium hydroxide, perchloric acid, and silver nitrate proved to be very suitable titrating agents for these titrations. The standard deviation of the determination of the investigated compounds was less than 0.9 % from those obtained with a glass electrode, i.e., silver electrode.