Nanomolar Determination of Methyldopa in the Presence of Large Amounts of Hydrochlorothiazide Using a Carbon Paste Electrode Modified with Graphene Oxide Nanosheets and 3-(4′-Amino-3′-hydroxy-biphenyl-4-yl)-acrylic Acid

Synthesis of New Azo Compounds and Their Application for a Simple Spectrophotometric Determination of Methyldopa Drug Using Anthranilic Acid and 2-Aminopyrimidine as Reagents

The goal of the current work is to synthesize methyldopa derivatives. Based on these reactions, two easy, speedy, accurate, inexpensive, and sensitive spectrophotometric approaches have been established for determining methyldopa (MED) in both pure and pharmaceutical forms. The proposed azo-coupling method depends on forming an azo compound between methyldopa drug and 2-AMPY or ANTH to produce two compounds of MED-2AMPY and MED-ANTH in the alkaline medium. The characterization of synthesized compounds utilizing UV-Visible and FT-IR spectra. FT-IR spectra of 2AMPY-MED confirm the existence of OH, C-Hor, C-Hal, NH, N=N, C=O, and C=C vibration at 3455, 3059, 2973, 3100, 1476,1692, and 1560 cm-1, and FT-IR spectra of ANTH-MED confirm the existence of OH, C-Hor, NH, C=O and N=N vibration at 3490, 3050, 3100, 1701 and 1462 cm-1, correspondingly. The obtained color of azo compounds is spectrophotometrically measured for the previously mentioned azo compounds at 450 and 455 nm, respectively. Under perfect conditions, the azo compound solutions exhibited molar absorptivities of 1563.0058 and 2091.0285 L.mol-1.cm-1, Sandell's sensitivity of 0.135 and 0.10 µg.cm-1, and Beer-Lambert's law are obeyed over the ranges 6.25- 62.5 mg. L-1 for the two developed procedures, respectively.

Determination of Methyldopa and Paracetamol in Pharmaceutical Samples by a Low Cost Genipa americana L. Polyphenol Oxidase Based Biosensor

Purpose: Jenipapo fruit (Genipa americana L) is a natural source of polyphenol oxidases (PPOs) whose potential in pharmaceutical analysis is noteworthy. Henceforth, this work reports the electrochemical study of a low-cost PPO-based biosensor produced from the crude extract of Jenipapo fruits and accounts a practical approach to employ this biosensor in the determination of methyldopa and paracetamol in pharmaceutical samples.

Methods: In order to investigate the electrochemical properties of the biosensor, theoretical and practical approaches were employed, and both samples and the biosensor were analyzed through electrochemical impedance spectroscopy (EIS) and voltammetric techniques, namely: differential pulse voltammetry (DPV) and cyclic voltammetry (CV).

Results: showcased that the biosensor presented good analytical features, as well as low detection limits (8 μmol L-1 for methyldopa and 5 μmol L-1 for paracetamol). The relative standard deviation was less than 5% mid-assay.

Conclusion: The use of this biosensor is a reliable, low cost and useful alternative in the pharmaceutic determination of phenolic drugs (e.g. methyldopa and paracetamol).

Electroanalysis of Catecholamine Drugs using Graphene Modified Electrodes

Background:

Catecholamine drugs are a family of electroactive pharmaceutics, which are widely analyzed through electrochemical methods. However, for low level online determination and monitoring of these compounds, which is very important for clinical and biological studies, modified electrodes having high signal to noise ratios are needed. Numerous materials including nanomaterials have been widely used as electrode modifies for these families during the years. Among them, graphene and its family, due to their remarkable properties in electrochemistry, were extensively used in modification of electrochemical sensors.

Objective:

In this review, working electrodes which have been modified with graphene and its derivatives and applied for electroanalyses of some important catecholamine drugs are considered.