New pencil graphite electrodes for potentiometric determination of fexofenadine hydrochloride and montelukast sodium in their pure, synthetic mixtures, and combined dosage form

This paper introduces the first electrochemical approach for the determination of Fexofenadine hydrochloride and Montelukast sodium as a combined form by constructing three new graphite electrodes coated with a polymeric membrane. The first electrode was constructed using ammonium molybdate reagent as an ion pair with fexofenadine cation for the determination of Fexofenadine drug, the second electrode was constructed using cobalt nitrate as an ion pair with montelukast anion for the determination of Montelukast drug, the third electrode was prepared by incorporating the two previously mentioned ion pairs in the same graphite sensor, which makes this sensor sensitive to each Fexofenadine and Montelukast drug. The coating material was a polymeric film comprises of Poly Vinyl Chloride (PVC), Di-butyl phthalate as a plasticizer (DBP), ion pairs of drugs with previously mentioned reagents. The electrodes showed a Nernstian response with a mean calibration graph slopes of [59.227, 28.430, (59.048, 28,643)] mv.decade⁻¹ for the three pencil electrodes respectively, with detection limits 0.025 μM for Fexofenadine and 0.019 μM for Montelukast drug which makes this method outperforms the reported method for the determination of this combination. The electrodes work effectively over pH range (2–4.5) for Fexofenadine hydrochloride and (5–9.5) for Montelukast sodium. The influence of the proposed interfering species was negligible as shown by selectivity coefficient values. The effectiveness of the electrodes continued in a period of time (45–69) days. The suggested sensors demonstrated useful analytical features for the determination of both drugs in bulk powder, in laboratory prepared mixtures and their combined dosage form. We have validated the method following ICH protocol, and we have reached very significant results in terms of the linearity, accuracy, selectivity, and precision of the method.

Improving the detection limits of antispasmodic drugs electrodes by using modified membrane sensors with inner solid contact

Three coated wire electrodes (CWEs) for the antispasmodic drugs; dicyclomine (Dc), mebeverine (Mv) and drotaverine (Dv) hydrochlorides were developed. Each electrode based on ion-associate of a heteropoly anion with the drug cation incorporated in membrane sensor modified with graphite and deposited on silver internal solid contact. The influence of addition of graphite to the membranes and the type of the internal solid contact on the potentiometric responses of the electrodes was investigated. The characteristics of the new electrodes were compared to the characteristics of previously reported traditional liquid inner contact electrodes of the same drugs. The lower detection limits of the proposed electrodes were somewhat better than those observed with the corresponding liquid contact ISEs and reached (1.2-2.0)x10(-7)M. The potentiometric selectivity of the CWEs revealed a significant improvement and much faster response times compared to the liquid contact ISEs. The practical utility of each electrode has been demonstrated by using it successfully in potentiometric determination of its respective drug in pharmaceutical preparations both in batch and flow injection conditions. Each electrode was also used as an indicator electrode in the potentiometric titration of the drug against standard silicotungstic acid and in potentiometric determination of the drug concentration in urine samples.

Salicylic acid determination in cow urine and drugs using a bienzymatic sensor

An enzymatic biosensor was developed for salicylic acid (salicylate ion) determined using a Clark type gas diffusion electrode and two enzymes (tyrosinase and salicylate hydroxylase) entrapped in a cellulose triacetate membrane. After optimization, the method was applied to the determination of salicylic acid in cow urine. Relatively good recoveries were achieved, between about 83% and 109%, using the calibration curve, and acceptable precision (R.S.D. about 8%). The method is now being tested for the determination of salicylic acid contained in commercially available drug specialities or galenic products. So far agreement with nominal values has been found to be between 75% and 110% with a R.S.D. of less than 8%.

Prospects of second generation artificial intelligence tools in calibration of chemical sensors

Multivariate data driven calibration models with neural networks (NNs) are developed for binary (Cu++ and Ca++) and quaternary (K+, Ca++, NO3- and Cl-) ion-selective electrode (ISE) data. The response profiles of ISEs with concentrations are non-linear and sub-Nernstian. This task represents function approximation of multi-variate, multi-response, correlated, non-linear data with unknown noise structure i.e. multi-component calibration/prediction in chemometric parlance. Radial distribution function (RBF) and Fuzzy-ARTMAP-NN models implemented in the software packages, TRAJAN and Professional II, are employed for the calibration. The optimum NN models reported are based on residuals in concentration space. Being a data driven information technology, NN does not require a model, prior- or posterior- distribution of data or noise structure. Missing information, spikes or newer trends in different concentration ranges can be modeled through novelty detection. Two simulated data sets generated from mathematical functions are modeled as a function of number of data points and network parameters like number of neurons and nearest neighbors. The success of RBF and Fuzzy-ARTMAP-NNs to develop adequate calibration models for experimental data and function approximation models for more complex simulated data sets ensures AI2 (artificial intelligence, 2nd generation) as a promising technology in quantitation.

Nitrate-selective membrane electrode based on bis(2-hydroxyanil)acetylacetone lead(II) neutral carrier

A nitrate-selective electrode based on a recently synthesized bis(2-hydroxyanil)acetylacetone lead(II) complex [(haacac)Pb] has been developed. Among different compositions studied, a membrane containing 30.7% poly(vinyl chloride) (PVC), 61.3% dibutyl phthalate (DBP) as a plasticizer, 3% methyltrioctylammonium chloride (MTOAC) as a cationic additive and 5% ionophore (all w/w) exhibited the best potentiometric response toward nitrate ion in aqueous solutions. The potentiometric response of the electrode was linear with a Nernstian slope of -58.8 mV decade(-1) within the NO3- concentration range of 2 x 10(-5)-1 x 10(-1) mol dm(-3). The response time of the electrode was < or =10 s over the entire linear concentration range of the calibration plot. The electrode is suitable for use within the pH range of 5.3-11. The selectivity coefficients for the proposed electrode were improved for some interferences, when compared with those of commercially available nitrate-selective electrodes.