Determination of Enalapril in Pharmaceuticals using Electrochemical Sensing with Amperometric Detection

In this work a new electrochemical method will be presented for the determination of enalapril in pharmaceutical tablets using unmodified screen printed electrode (SPE). The studies were done using amperommetric detection. Enalapril provides well defined, ovalshape oxidation peak at +1.05 V (vs. Ag/AgCl, 3.0 M KCl) in Britton-Robinson buffer solution (BRBS) at pH 5.0. After optimization of the experimental conditions, the influence of most common interferent compounds was tested. Under optimized experimental conditions, the signals were linearly proportional to the concentration of enalapril in the range from 2.5 to 90 mu M with a detection limit of 0.9 mu M. Repeatability of ten replicate measurements of 5 mu M enalapril was estimated to be 1.5%. Proposed method was successfully applied for the determination of the total amount of enalapril content in pharmaceutical preparations. Nevertheless, proposed method could be beneficial for the quick quantifications of enalapril in drugs using unmodified SPE electrode without any further treatment

Simple and Effective Procedure for Immobilization of Oxidases onto MnO2-bulk-modified, Screen-printed Carbon Electrodes

Nafion(R) film entrapment of oxidases onto the surface of MnO2-(5%, m:m) bulk-modified, screen-printed carbon electrodes was studied taking the inexpensive glucose oxidase as a model enzyme. The Nafion(R)-enzyme film was formed by drop-coating the suspension onto the surface of the electrode. Comparisons weremadeamong biosensors developed by using as-received, neutralized, and diluted (to 1% in methanol, ethanol or phosphate buffer) Nafion(R) in a flow injection (FI) mode. The amperometric response to injections of standard glucose solution was the highest for biosensors produced using neutralized Nafion(R). The effect of enzyme load per electrode (10-1190 mg) was investigated and 50 mg enzyme in the film per electrode was found to produce very good sensitivity as well as to be economical. Good reproducibility was achieved for three different biosensors (RSD of the means = 5.7%). The operational parameters for the glucose biosensor produced with this immobilization procedure were assessed and figures of merit obtained at the selected parameters. It has been observed that the effect of Nafion(R) to repel interfering ions like ascorbate and urate was lacking in this system. A preliminary investigation incorporating a hydrogen peroxide permselective membrane layer prior to enzyme immobilization gave promising result with polyurethane. South African Journal of Chemistry Vol.57 2004: 1-

A Stable Glutamate Biosensor Based on MnO2 Bulk-modified Screen-printed Carbon Electrode and Nafion(R) Film-immobilized Glutamate Oxidase

An amperometric glutamate biosensor was developed using screen-printed carbon electrodes bulk-modified with MnO2 (5%, m:m) onto which glutamate oxidase was immobilized via Nafion(R) film entrapment. The analytical performance of the biosensor was assessed in a flow injection mode and peak heights of the current response were used to evaluate results. Best responses were recorded at an applied potential of 440 mV (vs Ag/AgCl) a flow rate of 0.2 mL min-1, and a pH of 7.75 of the carrier (0.1 mol L-1 phosphate buffer). The calibration curve exhibited linearity in the concentration range 10-160 mg L-1, with a detection limit (as 3s value) of 1.7mg L-1, and a relative standard deviation 3.3% (c=20 mg L-1, n=10). This biosensor was used for the determination of monosodium glutamate in food seasonings, and the values obtained were similar to those obtained with spectrophotometry. The biosensor exhibited extraordinary stability when left on the FI system at a flow rate of 0.1 mL min-1 at room temperature retaining 50% of the original response towards glutamate even after 65 days. Stored in the working buffer for more than 60 days, the same biosensor showed extended linear range, 20-710 mg L-1. This 'aged' (stored) biosensor was used to determine monosodium glutamate in food seasonings and gave similar result to those obtained with a freshly prepared biosensor. (South African Journal of Chemistry: 2003 56: 54-59

Supplementary data for article: Stanković, D. M.; Mehmeti, E.; Svorc, L.; Kalcher, K. Simple, Rapid and Sensitive Electrochemical Method for the Determination of the Triketone Herbicide Sulcotrione in River Water Using a Glassy Carbon Electrode. Electroanalysis 2015, 27 (7), 1587–1593. https://doi.org/10.1002/elan.201400729

Supporting information for: [https://doi.org/10.1002/elan.201400729]Related to published version: [http://cherry.chem.bg.ac.rs/handle/123456789/1731

Supplementary data for article: Mehmeti, E.; Stanković, D. M.; Ortner, A.; Zavašnik, J.; Kalcher, K. Highly Selective Electrochemical Determination of Phlorizin Using Square Wave Voltammetry at a Boron-Doped Diamond Electrode. Food Analytical Methods 2017, 10 (11), 3747–3752. https://doi.org/10.1007/s12161-017-0935-x

Supplementary material for: [https://doi.org/10.1007/s12161-017-0935-x]Related to published version: [http://cherry.chem.bg.ac.rs/handle/123456789/2531

Supplementary data for the article: Lakic, M.; Vukadinovic, A.; Kalcher, K.; Nikolic, A. S.; Stankovic, D. M. Effect of Cobalt Doping Level of Ferrites in Enhancing Sensitivity of Analytical Performances of Carbon Paste Electrode for Simultaneous Determination of Catechol and Hydroquinone. Talanta 2016, 161, 668–674. https://doi.org/10.1016/j.talanta.2016.09.029

Supplementary material for: [https://doi.org/10.1016/j.talanta.2016.09.029]Related to published version: [http://cherry.chem.bg.ac.rs/handle/123456789/2343

Electrocatalytic Oxidation of Nitric Oxide at Carbon Paste Electrode Modified with Chromium (III) Oxide

Chromium (III) oxide was used as a bulk mediator in carbon paste electrodes to improve the better performance of the carbon electrodes for the detection of nitric oxide in comparison with unmodified electrodes. The reaction mechanism of the electrocatalytic oxidation of NO at the modified electrode was studied using cyclic voltammetry and differential pulse voltammetry. The chemical sensor could be operated under physiological conditions (pH 7.5, 0.1 M phosphate buffer), with an operating potential of 750 mV (vs. Ag/AgCl), in hydrodynamic amperometry. The amperometric response of the sensor showed good linearity up to 200 mmol/L with a detection limit (3σ) of 0.69 mmol/L. The effect of the interferent nitrite was not fatal and could be eliminated by the use of the standard addition method. The new chemical sensor seems also promising to detect NO in car exhaust fumes

Supplementary data for article: Mehmeti, E.; Stanković, D. M.; Chaiyo, S.; Zavasnik, J.; Žagar, K.; Kalcher, K. Wiring of Glucose Oxidase with Graphene Nanoribbons: An Electrochemical Third Generation Glucose Biosensor. Microchimica Acta 2017, 184 (4), 1127–1134. https://doi.org/10.1007/s00604-017-2115-5

Supplementary material for: [https://doi.org/10.1007/s00604-017-2115-5]Related to published version: [http://cherry.chem.bg.ac.rs/handle/123456789/2438

Supplementary data for the article: Stanković, V.; Đurđić, S.; Ognjanović, M.; Mutić, J.; Kalcher, K.; Stanković, D. M. A Novel Nonenzymatic Hydrogen Peroxide Amperometric Sensor Based on AgNp@GNR Nanocomposites Modified Screen-Printed Carbon Electrode. Journal of Electroanalytical Chemistry 2020, 876, 114487. https://doi.org/10.1016/j.jelechem.2020.114487

Supplementary material for: [https://doi.org/10.1016/j.jelechem.2020.114487]Related to published version: [http://cherry.chem.bg.ac.rs/handle/123456789/4033

A new amperometric ß-ODAP biosensor

Introduction The Lathyrus/lathyrism challenge is broad-based by its nature and requires multi-disciplinary efforts of specialists in the field of epidemiology, neurology, biochemistry, chemistry, nutrition, and agronomy. The role of chemists is in systematic determination of minor natural products in L. sativus seeds so that the sole responsibility of ß-ODAP for neurolathyrism is ascertaine