Potentiometric and thermal studies of a coated-wire benazepril-selective electrode

Comparative Study of Potassium Ion-Selective Electrodes with Solid Contact: Impact of Intermediate Layer Material on Temperature Resistance

This paper presents a comparative study on the temperature resistance of solid-contact ion-selective electrodes, depending on the type of solid-contact material. Five types of potassium electrodes, with a valinomycin-based model membrane, were developed using different types of mediation layers, namely a conductive polymer (poly(3-octylthiophene-2,5-diyl) and a perinone polymer), multi-walled carbon nanotubes, copper(II) oxide nanoparticles, and a nanocomposite consisting of multi-walled carbon nanotubes and copper(II) oxide. We examined how the measurement temperature (10 °C, 23 °C, and 36 °C) affects the sensitivity, measurement range, detection limit, selectivity, as well as the stability and reversibility of the electrode potential. Electrodes modified with a nanocomposite (GCE/NC/ISM) and a perinone polymer (GCE/PPer/ISM) showed the best resistance to temperature changes. An almost Nernst response and a stable measurement range and the lowest detection limit values for each temperature were obtained for them. The introduction of mediation layers significantly improved the stability and potential reversibility of all the modified electrodes relative to the unmodified electrode (GCE/ISM). Still, it was the GCE/PPer/ISM and GCE/NC/ISM that stood out from the others, with stability of 0.11 and 0.12 µV/s for 10 °C, 0.05 and 0.08 µV/s for 23 °C, and 0.06 and 0.09 µV/s for 36 °C, respectively.

A novel coated platinum electrode for oseltamivir determination in pharmaceuticals

New coated platinum selective electrodes have been prepared and used for the determination of oseltamivir phosphate (OSL) in bulk drug solutions and in pharmaceutical preparations. Electrodes were using plasticized PVC membranes doped with ion-pair complexes based on drug-phosphomolybdate and drug-tetraphenylborate as electroactive materials. The influence of membrane composition (plasticizers and ion-pair complexes) has been investigated. Optimum performance was obtained for two polymeric membranes: PVC:o-NPPE:OSL-TPB in the ratio of 30:68:2 (%, w:w:w) and PVC:DPP:OSL-PMA in the ratio of 30:68:2 (%, w:w:w). The electrodes exhibited linear responses over large concentration ranges (1.0×10(-5)-1.0×10(-2) and 5.0×10(-5)-5.0×10(-2)M, respectively) with near-Nernstian responses (58.9 and 57.3mV/decade, respectively). The selectivity coefficients indicated good selectivity for OSL drug over a large number of organic compounds and some inorganic cations. The proposed electrodes were successfully applied to the determination of OSL in raw material and in pharmaceutical formulations. The results were validated by comparison with a capillary electrophoresis method.

Potentiometric membrane sensor based on 6-(4-nitrophenyl)-2,4-diphenyl-3,5-diaza-bicyclo[3.1.0]hex-2-ene for detection of Sn(II) in real samples

A Sn2+ ion-selective electrode which was prepared with a polymeric membrane based on 6-(4-nitrophenyl)-2,4-diphenyl-3,5-diaza-bicyclo[3.1.0]hex-2-ene (NDDBH) as a ionophore. Effects of experimental parameters such as membrane composition, nature and amount of plasticizer, the amount of additive and concentration of internal solution on the potential response of Sn2+ sensor were investigated. The electrode exhibited a Nernstian slope of 28.8+/-1.1 mV/decade of Sn2+ over a concentration range of 1.0 x 10(-5) to 1.0 x 10(-1) M of Sn2+ in an acidic solution (pH 1). The limit of detection was 4.0 x 10(-6) M. The results show that this electrode can be used in ethanol media until 20% (v/v) concentration without interference. It can be used for more than 6 weeks without any considerable divergence in the potentials. The proposed membrane electrode revealed very good selectivity for Sn(II) ions over a wide variety of other cations and could be used in acidic media. The standard electrode potentials were determined at different temperatures and used to calculate the isothermal coefficient of the electrode. The stability constant (log K(s)) of the Sn(II)-ionophore complex was determined at 25 degrees C by potentiometric titration in mixed aqueous solution. It was used as indicator electrode in potentiometric determination of Sn(II) ion in real samples.

Stability indicating RP-HPLC method for simultaneous determination of amlodipine and benazepril hydrochloride from their combination drug product

A stability indicating reversed-phase HPLC method has been developed and subsequently validated for simultaneous estimation of amlodipine (AM) present as amlodipine besylate (AB), and benazepril hydrochloride (BH) from their combination product. The proposed RP-HPLC method utilizes a Zorbax SB C18, 5 microm, 250 mm x 4.6 mm i.d. column, mobile phase consisting of phosphate buffer and acetonitrile in the proportion of 65:35 (v/v) with apparent pH adjusted to 7.0, and UV detection at 240 nm using a photodiode array detector. AB, BH, and their combination drug product were exposed to thermal, photolytic, hydrolytic, and oxidative stress conditions, and the stressed samples were analysed by the proposed method. Peak homogeneity data of AM and BH peaks obtained using photodiode array detector, in the stressed sample chromatograms, demonstrated the specificity of the method for their estimation in presence of degradants. The described method was linear over a range of 6-14 microg/ml for AM and 12-28 microg/ml for BH. The mean recoveries were 99.91 and 100.53% for AM and BH, respectively. F-test and t-test at 95% confidence level were used to check the intermediate precision data obtained under different experimental setups; the calculated value was found to be less than critical value.