High Performance Liquid Chromatographic Determination of Diuretic-Antihypertensive Combination Products. I. Prazosin and Polythiazide

Ion-selective electrode for the determination of prazosin in tablets

A poly (vinylchloride) (PVC) membrane electrode selective for prazosinium cation based on prazosinium-phosphotungstate (PZ)(3)PT ion-associate is prepared. The electrode exhibits a linear response with an approximate Nernstian slope over the range of 2.7 x 10(-6)-10(-2) M. Calibration graph slope of the electrode is 58 mV PZ(-1) concentration decade when preconditioned by soaking in distilled water for 1 h-20 days. The working pH of the electrode ranged from 1.5 to 6.4 and exhibits very good selectivity for the PZ with respect to a large number of inorganic cations and organic substances of biological importance. The standard additions method and potentiometric titration are used to determine the PZ in pure solution and in pharmaceutical preparations with satisfactory results.

Voltammetric and spectrophotometric techniques for the determination of the antihypertensive drug Prazosin in urine and formulations

A sensitive method was developed to determine Prazosin using a nafion modified carbon paste electrode (NMCPE). Prazosin was accumulated at a potential of 750 mV in Britton-Robinson buffer (pH 6.0) and then a negative sweep was made obtaining a cathodic peak close to 0 V. Cyclic voltammetric studies indicated that the process was quasi-reversible, and fundamentally controlled by adsorption. To obtain a good sensitivity, the instrumental and accumulation variables were studied using differential pulse voltammetry (DPV). Adsorptive voltammetric peak currents showed a linear response for Prazosin concentrations in the range between 4.0 x 10(-11) and 4.0 x 10(-8) M with two different slopes, and a detection limit (LOD) of 3.1 x 10(-11)M was obtained. The variation coefficient (CV) for a 8.0 x 10(-10) M solution (n = 10) was 4.08%. A spectrophotometric study of Prazosin was also carried out and two absorption bands were obtained at 246 and 329 nm (pH 1.8). The band at 329 nm was pH-dependent and its height and position changed with the pH values, so this allowed the pK'a determination (7.14 +/- 0.20) using different methods. The detection limit reached by means of UV-spectrophotometry was 0.9 x 10(-7) M, and the variation coefficient for 1.5 x 10(-5) M Prazosin solutions was 1.14% (n = 10). Although the sensitivity of the UV-spectrophotometric method was lower than that obtained using adsorptive stripping-differential pulse voltammetry (AdS-DPV), it could be applied to the determination of Prazosin in Minipres tablets. The voltammetric method was used for the determination of the drug in human urine samples at trace levels with good recoveries.

Spectrophotometric determination of some pharmaceutical piperazine derivatives through charge-transfer and ion-pair complexation reactions

Simple and sensitive spectrophotometric methods are described for the assay of three piperazine derivatives; ketoconazole, piribedil and prazosin hydrochloride based on charge-transfer and ion-pair complexation reactions. The first method is based on the reaction of the basic drug with 2,3-dichloro-5,6-dicyano-p-benzoquinone (DDQ) in acetonitrile. The orange-red colour formed due to the formation of charge-transfer complex showed maximum absorbance at 460 nm. The second method is based upon the interaction of the basic drug in dry chloroform with bromophenol blue (BPB) in the same solvent to produce a stable yellow ion-pair complex which absorbs at 410 nm. Beer's law was obeyed for both methods and the relative standard deviations were found to be less than 1%. The two methods can be applied to the analysis of tablets, with no evidence of interference from excipients. A more detailed investigation of the complex was made with respect to its composition, association constant and free energy change.

Spectrophotometric study of polythiazide-palladium (II) complex

A quantitative spectrophotometric method using Pd(II) chloride as analytical reagent for the determination of polythiazide in pharmaceutical preparations is described in this study. It has been found that polythiazide reacts with Pd(II) chloride in the pH range 3.6-5.8, forming a red, water-soluble (1:1) complex with maximum absorbance at 527 nm. At the optimum pH of 4.8 and an ionic strength mu = 0.1 M, the conditional stability constant of the complex is found to be log K' = 4.77. The molar absorptivity at 527 nm is 3.2 x 10(3) l mol-1 cm-1. Good agreement with Beer's law was found for polythiazide concentrations up to 2.2 mmol l-1. The nominal percent recovery of polythiazide was 99.5% (n = 20). The simplicity, selectivity and sensitivity of the method described is suitable for rapid and accurate determinations of polythiazide in tablets.