Voltammetric determination of pyridoxine (Vitamin B6) at a carbon paste electrode modified with vanadyl(IV)–Salen complex

Electrochemical Sensors Containing Schiff Bases and their Transition Metal Complexes to Detect Analytes of Forensic, Pharmaceutical and Environmental Interest. A Review

Schiff bases and their transition metal complexes are inexpensive and easy to synthesize. These compounds display several structural and electronic features that allow their application in numerous research fields. Over the last three decades, electroanalytical scientists of various areas have developed electrochemical sensors from many compounds. The present review discusses the applicability of Schiff bases, their transition metal complexes and new materials containing these compounds as electrode modifiers in sensors to detect analytes of forensic, pharmaceutical and environmental interest. In forensic sciences, Schiff bases are mainly used to analyze illicit drugs: chemical reactions involving Schiff bases can help to elucidate illicit drug production and to determine analytes in seized samples. In the environmental area, given that most methodologies provide Limit of Detection (LOD) values below the values recommended by regulatory agencies, Schiff bases constitute a promising strategy. As for pharmaceutical applications, Schiff bases represent an approach for analysis of complex biological samples containing low levels of the target analytes in the presence of a large quantity of interfering compounds. This review will show that new highly specific materials can be synthesized based on Schiff bases and applied in the pharmaceutical industry, toxicological studies, electrocatalysis and biosensors. Most literature papers have reported on Schiff bases combined with carbon paste to give a chemically modified electrode that is easy and inexpensive to produce and which displays specific and selective sensing capacity for different applications.

Highly sensitive interference-free electrochemical determination of pyridoxine at graphene modified electrode: Importance in Parkinson and Asthma treatments

To reduce the side effects in the medication of Parkinson and Asthma, pyridoxine (PY) is administered along with l-3,4-dihydroxyphenyl alanine (l-dopa) and theophylline (TP), respectively. However, excessive dosage of PY leads to nervous disorder. Thus, a sensitive and selective electrochemical method was developed for the determination of PY in the presence of major interferences including TP, l-dopa, ascorbic acid (AA) and riboflavin (RB) using electrochemically reduced graphene oxide (ERGO) film modified glassy carbon electrode (GCE) in this paper. The ERGO fabrication process involves the nucleophilic substitution of graphene oxide at basic pH on amine terminal of 1,6-hexadiamine which was pre-assembled on GCE followed by electrochemical reduction. The electrocatalytic activity of the ERGO modified electrode was examined towards the oxidation of PY. It greatly enhanced the oxidation current of PY in contrast to bare and GO modified GCEs due to facile electron transfer besides π-π interaction between ERGO film and PY. Since TP and l-dopa drugs antagonize the drug action of PY, ERGO modified GCE was also used for the simultaneous determination of PY and l-dopa and PY and TP. Further, the selective determination of PY in the presence of other water soluble vitamins such as ascorbic acid and riboflavin was also demonstrated. Using amperometry, detection of 100nM PY was achieved and the detection limit was found to be 5.6×10(-8)M (S/N=3). The practical application of the present method was demonstrated by determining the concentration of PY in human blood serum and commercial drugs.

Application of the high-performance liquid chromatography method with coulometric detection for determination of vitamin B(6) in human plasma and serum

A reversed-phase high-performance liquid chromatography method (HPLC) with coulometric electrochemical detection has been developed and validated for the simultaneous analysis of pyridoxamine-5'-phosphate (PMP), pyridoxamine (PM), pyridoxal 5'-phosphate (PLP), pyridoxal (PL), pyridoxine (PN) and 4-pyridoxic acid (4-PA) in human plasma and serum. The isocratic separation was achieved on C(18) column (250mmx4.6mm, I.D., 5microm) with a mobile phase consisted of 35mM sodium phosphate containing 2.5mM heptanesulfonic acid, adjusted to pH 3.2 with 85% orthophosphoric acid and 12% methanol (v/v). Within-run and between-run precisions expressed by the relative standard deviations were less than 2.7% and 7.7% for all the analysed vitamins and 4-PA, respectively. The limits of detection (LOD) and quantification (LOQ) were: 0.8 and 2.6nM, 1.1 and 3.8nM, 1.5 and 4.5nM, 1.3 and 4.2nM, 1.1 and 3.7nM, 2.1 and 6.3nM for PMP, PM, PLP, PL, PN and 4-PA, respectively. The recoveries ranged from 90.4% to 98.4%. Stability of vitamins was checked under a variety of storage conditions. The developed application demonstrated acceptable sensitivity, precision, accuracy, stability, and linearity over the physiological concentration range. The major advantage of the proposed method is its great simplicity.

High-performance liquid chromatography method for the simultaneous determination of thiamine hydrochloride, pyridoxine hydrochloride and cyanocobalamin in pharmaceutical formulations using coulometric electrochemical and ultraviolet detection

The method for the simultaneous determination of thiamine hydrochloride, pyridoxine hydrochloride and cyanocobalamin by high-performance liquid chromatography (HPLC) with coulometric electrochemical and UV detections is presented. The retention time of vitamins was repeatedly determined by isocratic elution using 0.05 M phosphate buffer-10% methanol and 0.018 M trimethylamine (1 ml min(-1), pH 3.55) as mobile phase with the Supelco LC 18 column 5 microm (25 cm x 4.6 mm). The specificity of the method was demonstrated by the retention characteristics, coulometric electrochemical and UV detection. The limits of detection of thiamine, pyridoxine and cyanocobalamin were: 9.2, 2.7 and 0.08 ng/ml, respectively. The method was characterized also by wide concentration range, high sensitivity and good accuracy (99.6-102.7%). The repeatability of the method was evaluated at different level of concentration of vitamins and the relative standard deviation was below 4.5%. The method was successfully applied for the quantification of Vitamins B1, B6 and B12 in pharmaceutical preparations and dietary supplements.

Phosphorus-doped and undoped glassy carbon indicator electrodes in controlled-current potentiometric titrations of bromide- or chloride-containing active ingredients in some pharmaceutical preparations

Phosphorus-doped glassy carbon (as a novel material) and glassy carbon (Sigri commercial sample) were applied as potentiometric indicator electrodes in the titrimetric determination of active components with bromide or chloride in their molecules in different pharmaceutical preparations (Buscopan, Prostigmine, Isoptin, Bedoxin, Akineton and Trodon). After the necessary pre-treatment of the electrode surfaces and sample dissolution, the halide was titrated with a standard solution of silver nitrate (indirect determination). Amounts of 10-20 micromol of the investigated active ingredients per titration were determined with a relative standard deviation that, depending on the nature of indicator electrode, determined molecules and filler components, was in the range of 0.3-2.7%. The results obtained were compared with those of the official methods and with those obtained by potentiometric titrations using silver electrode. The titrimetric procedures developed are relatively fast, easy, economical and can be used to analyse of a large number of pharmaceutical products.

Voltammetric determination of pyridoxine (Vitamin B6) by use of a chemically-modified glassy carbon electrode

A novel carbon nanotube-modified glassy carbon electrode was described for the direct determination of pyridoxine. The electrochemical behavior of pyridoxine was investigated, and a well-defined oxidation peak with high sensitivity was observed at the modified electrode. Owing to the unique structure and extraordinary properties of multi-wall carbon nanotube (MWNT), the MWNT-modified glassy carbon electrode shows obvious electrocatalytic activity to the oxidation of pyridoxine, since it greatly enhances the oxidation peak current of pyridoxine as well as lowers its oxidation overpotential. Based on this, a very sensitive and simple voltammetric method was developed for the measurement of pyridoxine. A sensitive linear voltammetric response for pyridoxine was obtained in the concentration range of 5 x 10(-7)-1 x 10(-4)mol/L, and the detection limit is 2 x 10(-7)mol/L using differential pulse voltammetry. Compared with other voltammetric methods, this proposed method possesses many advantages such as very low detection limit, fast response, low cost and simplicity. The practical application of this new analytical method was demonstrated with pyridoxine drugs.