A micellar liquid chromatographic procedure for the determination of amiloride, bendroflumethiazide, chlorthalidone, spironolactone and triamterene in pharmaceuticals

Spironolactone voltammetric determination on renewable amalgam film electrode

In this study a new high sensitive method of spironolactone (SP) determination is proposed using voltammetric technique. As the working electrode amalgam film silver based electrode (Hg(Ag)FE) was applied, that resulted in obtaining low limit of spironolactone detection, ex. for the preconcentration time 45 s obtained detection limit was 4.7·10^-9 mol L^-1 (1.96·10^-6 g L^-1). The linear response of spironolactone signal on mercury film electrode was obtained in the range of concentration from 15·10^-9 to 3.0·10^-6 mol L^-1 and the obtained repeatability measured as RSD was very good, with the value of 2.0% (n = 5; concentration 0.5·10^-6 mol L^-1). The proposed method was successfully applied and validated by studying the recovery in commercially available pharmaceutical formulations containing known amount of spironolactone.

Direct determination of triamterene by potentiometry using a coated wire selective electrode

A coated wire triamterene-selective electrode based on the incorporation of a triamterene-tetraphenylborate ion-pair in a poly(vinylchloride) coating membrane was constructed. The influence of membrane composition, temperature, pH of the test solution, and foreign ions on the electrode performance were investigated. The electrode showed a Nernstian response over a triamterene concentration range from 1.0 x 10(-6) to 3.5 x 10(-2) M, at 25 degrees C, and was found to be very selective, precise, and usable within the pH range 4.5-7.5. The standard electrode potentials, E degrees, were determined at 15, 20, 25, 30, 35, 40 and 45 degrees C and used to calculate the isothermal temperature coefficient (dE degrees /dt) of the electrode. Temperatures higher than 45 degrees C seriously affected the electrode performance. The electrode was successfully applied to the potentiometric determination of triamterene hydrochloride both in pure solutions and in pharmaceutical preparations.

Simultaneous direct determination of amiloride and triamterene in urine using isopotential fluorometry

A method for the simultaneous fluorometric determination of two diuretics in urine is proposed. The combination of matrix isopotential synchronous fluorescence (MISF) and first derivative techniques provides good analytical results. MISF spectra are obtained by calculating the isopotential trajectory in the three-dimensional fluorescence spectrum for a urine solution. In the spectral contour, the trajectory is taken to be the portion of the line that passes by the fluorescence maxima of both diuretics (lambda(ex) = 365 and lambda(em) = 413 nm for amiloride and lambda(ex) = 365 and lambda(em) = 437 nm for triamterene). Because contour lines connect points of identical intensity and the trajectory is part of a contour line, it is called "isopotential." Analyses was carried out in a 1/1 (v/v) ethanol/water mixture, using an apparent pH of 6.3 provided by 0.01 M sodium/citrate citric acid buffer. Urine samples are diluted 50 times and provide linear calibration plots at amiloride and triamterene concentrations up to 320 and 100 ng mL(-1), respectively. The goodness of the analytical signal was checked by using variance analysis. Signals recorded throughout the calibration range were subjected to three calibrations per each analyte, both in the absence and in the presence of variable amounts of the other analyte. Differences between individual calibrations and slopes were compared with those within individual calibrations. Based on the results, triamterene and amiloride can be accurately quantified in the presence of each other. The limit of detection calculated according to Clayton who uses error propagation throughout the calibration curve and a noncentralized security factor was 16.8 and 2.4 ng mL(-1) for amiloride and triamterene, respectively.

Comparison of the performance of butanol and pentanol as modifiers in the micellar chromatographic determination of some phenethylamines

A procedure was developed for the determination of several phenethylamines (amphetamine, arterenol, ephedrine, phenylephrine, phenylpropanolamine, mephentermine, methoxyphenamine, pseudoephedrine and tyramine), using micellar mobile phases of sodium dodecyl sulfate (SDS), a C18 column and UV detection. The drugs were eluted at short retention times with conventional acetonitrile-water or methanol-water mobile phases. In contrast, in the micellar system, they were strongly retained due to association with the surfactant adsorbed on the stationary phase, and needed the addition of butanol or pentanol to be eluted from the column. These modifiers allowed a simple way of controlling the retention. The chromatographic efficiencies obtained with the hybrid mobile phases of SDS-butanol and SDS-pentanol were also very high, mostly in the N=3000-7000 range, significantly greater than those achieved with a conventional acetonitrile-methanol-water mobile phase. Butanol and pentanol yielded similar selectivities, but the latter modifier permitted significantly shorter retention times than butanol, and was preferred to expedite the analysis of the pharmaceuticals. Most binary combinations of the nine phenethylamines can be resolved with these mobile phases. A mobile phase of 0.15 M SDS-5% pentanol was used to assay five of the phenethylamines (amphetamine, ephedrine, phenylephrine, phenylpropanolamine and pseudoephedrine) in 22 pharmaceutical preparations, which contained diverse accompanying compounds. The results agreed with the declared compositions and with those obtained with a mobile phase of methanol-acetonitrile-0.05 M phosphate buffer (pH 3) 10:5:85, with no interferences and relative errors usually below 2%. However, with the aqueous-organic mobile phase, the retention time for phenylephrine was too low and could not be usually evaluated.

Reliability of the capacity factor at zero micellar concentration and the solute-micelle association constant estimates by micellar liquid chromatography

In micellar liquid chromatography, MLC, the hydrophobicity of a compound is the predominant effect on its retention and interaction with micelles. The capacity factors at zero micellar concentration, k(m), and the solute-micelle association constants, KAM- have recently been used as the hydrophobicity index of compounds and are important in QSAR studies. These parameters could be estimated (by regression) from the (k,[M]) data, where k is the capacity factor and [M] the surfactant concentration minus the critical micelle concentration. km and KAM are usually obtained from the intercept and slope, respectively, of the plot 1/k vs. [M]. In spite of the general use of this equation, the reliability of the estimates has not received special attention. Two new regression models have been proposed: a nonlinear model (plot k vs. [M]) and a new linear model (k vs. k.[M]). The reliability of the km and KAM estimates is studied with the aid of simulated data, and the conclusions obtained from the theoretical study are contrasted with experimental data. The influence of variables like the hydrophobicity of compounds, the KAM/km ratio, the uncertainty of experimental k data and the experimental design have been considered. Some critical aspects of the models and recommendations for their use are provided.

Performance of micellar mobile phases in reversed-phase chromatography for the analysis of pharmaceuticals containing beta-blockers and other antihypertensive drugs

A rapid and simple reversed-phase micellar liquid chromatographic procedure for the simultaneous determination of the beta-blockers atenolol, metoprolol and oxprenolol, the diuretics amiloride, bendroflumethiazide, chlorthalidone and hydrochlorothiazide and the vasodilator hydralazine in pharmaceuticals, is proposed. An interpretive optimization procedure, which uses the chromatographic data for only five mobile phases, was applied to select a suitable micellar mobile phase. A comparative study was also made of the performance of micellar and aqueous-organic mobile phases in the analysis of pharmaceuticals that combine beta-blockers and diuretics. The determination of all the drugs could be made with a micellar mobile phase of 0.15 mol l-1 sodium dodecyl sulfate and 7% propanol in 0.01 mol l-1 phosphate buffer at pH 3, with retention times below 20 min, whereas two different aqueous-organic mobile phases were needed to make the same analyses.

High-performance micellar liquid chromatography determination of sulphonamides in pharmaceuticals after azodye precolumn derivatization

A chromatographic procedure with precolumn derivatization to form the N-(1-naphthyl)ethylenediamine dihydrochloride azodyes is proposed for the analysis of several sulphonamides (sodium sulphacetamide, sulphadiazine, sulphaguanidine, sulphamerazine, sulphamethizole, sulphamethoxazole, sulphanilamide and sulphathiazole) in pharmaceutical preparations (tablets, pills, capsules, suspensions and drops). The separation is performed with a 0.05 M sodium dodecyl sulphate/2.4% pentanol eluent at pH 7. The precolumn derivatization improved the resolution in the chromatograms and increased the selectivity in the determination of mixtures of sulphonamides and in preparations where other drugs were present. The derivatization reaction was readily performed in a micellar medium of SDS at pH 1, leading to a rapid and simple procedure. The recoveries were in the 97-104% range with relative standard deviations usually below 3%.