Electrochemical oxidation of tiopronin at diamond film electrodes and its determination by amperometric flow injection analysis

Design of cobalt-doped graphene quantum dot-decorated vanadium pentoxide nanosheet-based Off-On fluorescent sensor system for tiopronin sensing

Despite the high medicinal value of tiopronin, there are substantial adverse effects such as yellow skin, yellow eyes, muscle aches, etc. Therefore, there is a huge necessity to identify tiopronin using advanced sensors in provided samples. Recently, the preference for graphene quantum dots (GQDs) and inorganic nanomaterial-based fluorescent sensors for the detection of pharmaceuticals has been extensively documented due to their plentiful advantages. Therefore, in this work, the cobalt-doped GQDs decorated vanadium pentoxide nanosheet-based fluorescence switch 'Off-On' sensor (Co-GQDs@V2O5-NS) was designed for highly sensitive and selective detection of tiopronin. Briefly, the green synthesis of highly fluorescent Co-GQDs was carried out using a hydrothermal method. Meanwhile, the synthesis of V2O5-NS was synthesized using the liquid exfoliation method. The synthesis of Co-GQDs@V2O5-NS was accomplished wherein Co-GQDs adsorbed on the surface of V2O5-NS that offered the quenching of fluorescence of Co-GQDs. Afterward, the addition of tiopronin into the quenched probe disclosed the proportional recovery of fluorescence of Co-GQDs. Here, the addition of tiopronin provides the decomposition of V2O5-NS and conversion into the V4+ that aids in releasing the quenched fluorescence of Co-GQDs. The limit of detection and linearity range for tiopronin was found to be 1.43 ng/mL and 10-700 ng/mL, respectively. Moreover, it demonstrated high selectivity, good stability at experimental conditions, and practicality in analyzing tiopronin in spiked sample analysis. Hence, the designed Co-GQDs@V2O5-NS nanosized sensor enables high sensitivity, selectivity, simplicity, label-free, and eco-friendly tiopronin recognition. In the future, the utility of Co-GQDs@V2O5-NS can open a new door for sensing tiopronin in provided samples.

Boron Doped Diamond Electrodes in Flow-Based Systems

Boron-doped diamond (BDD) electrodes present several notable properties, such as the largest potential window of all electrode materials (especially in anodic potentials), low background and capacitive currents, reduced fouling compared to other electrodes, mechanical robustness, and good stability over time. On the other hand, flow-based systems are known as well-established approaches to minimize reagent consumption and waste generation and with good compromise between sample throughput and analytical performance (mechanization of chemical assays). This review focuses on the use of BDD electrodes for electrochemical detection in flow systems, such as flow injection analysis (FIA), batch injection analysis (BIA), high performance liquid chromatography (HPLC), and capillary electrophoresis (CE). The discussion deals with the historical evolution of BDD, types of electrochemical pre-treatments (cathodically/H-terminated or anodically/O-terminated), cell configurations, and analytical performance. Articles are discussed in chronological order and subdivided according to the type of flow system: FIA, BIA, HPLC, and CE.

Determination of thiamazole in pharmaceutical samples by phosphorus molybdenum blue spectrophotometry

A novel method is established to determine thiamazole by phosphorus molybdenum blue spectrophotometry. The experiment indicates that PO(4)(3-) reacts with Mo(7)O(24)(6-) in 0.30mol/L H(2)SO(4) solution to form a product with phosphorus-molybdenum heteropoly acid ([H(2)PMo(12)O(40)](-)). Then [H(2)PMo(12)O(40)](-) is deoxidized to form phosphorus molybdenum blue (H(3)PO(4)·10MoO(3)·Mo(2)O(5)) by thiamazole. The amount of thiamazole can be determined based on the absorbance of phosphorus molybdenum blue (λ(max)=710nm). A good linear relationship is obtained between the absorbance and the concentration of thiamazole in the range of 0.035-70μg/mL. The equation of the linear regression is A=0.03384+0.00834c (μg/mL), with a linear correlation coefficient of 0.9990. The apparent molar absorption coefficient is 1.0×10(3)L/(molcm). The method has been successfully applied to the determination of thiamazole in pharmaceutical samples with satisfactory results, and recoveries are in the range of 99.6-100.6%.

A highly sensitive fluorescent probe for tiopronin based on the cleavage of 2, 4-dinitrobenzenesulfonate

A highly sensitive fluorogenic probe for tiopronin was proposed. 2,4-Dinitrobenzenesulfonyl-fluorescein (I) is an almost nonfluorescent compound. Upon mixing with tiopronin in aqueous solution, the 2,4-dinitrobenzenesulfonyl group of I was efficiently removed and its parent dye fluorescein was released, hence leading to dramatic increases in both fluorescence and absorbance of the reaction mixture. Under optimal conditions, the fluorescence increase is linear with tiopronin concentration in the range 5.0-600 ng mL(-1), with a detection limit of 1.5 ng mL(-1) (3sigma). The proposed method has been successfully applied to tiopronin determination in pharmaceutical preparations and in spiked human urine samples.

Validation of a tubular bismuth film amperometric detector

A tubular bismuth film electrode (BFE), installed as part of a multisyringe flow injection system, was used as an amperometric detector to determine the concentration of diclofenac sodium in pharmaceutical formulations. A tubular voltammetric detection cell was employed, in which the hydrodynamic flow conditions were not disturbed. This automated method allows the continuous regeneration of the BFE, preventing passivation of the detector and improving the sensitivity of detection. The influence of several variables on this sensitivity, such as the injection volume, deposition time and flow rate were evaluated; a two-level factorial experimental design was employed for this. In optimal conditions, the linear range of the calibration curve varied from 6.0-50.0 micromol L(-1), with a detection limit of 4.3 micromol L(-1). A sampling rate of 90 determinations/h was achieved; the relative standard deviation of analytical repeatability was <3.5%. After 30 injections the bismuth film on the electrode surface was automatically renewed. The method was validated by comparing the results obtained with those provided by RP-HPLC; no significant difference were seen (p<0.05).

Cost-Effective Flow Cell for the Determination of Malachite Green and Leucomalachite Green at a Boron-Doped Diamond Thin-Film Electrode

An electrooxidation and a cost-effective flow-based analysis of malachite green (MG) and leucomalachite green (LMG) were investigated at a boron-doped diamond thin-film (BDD) electrode. Cyclic voltammetry as a function of the pH of the supporting electrolyte solution was studied. Comparison experiments were performed with a glassy carbon electrode. A well-defined cyclic voltammogram, providing the highest peak current, was obtained when using phosphate buffer at pH 2. The potential sweep-rate dependence of MG and LMG oxidation (peak currents for 1 mM MG and LMG linearly proportional to v 1/2, within the range of 0.01 to 0.3 V/s) indicates that the oxidation current is a diffusion-controlled process on the BDD surface. In addition, hydrodynamic voltammetry and amperometric detection using the BDD electrode combined with a flow injection analysis system was also studied. A homemade flow cell was used, and the results were compared with a commercial flow cell. A detection potential of 0.85 V was selected when using a commercial flow cell, at which MG and LMG exhibited the highest signal-to-background ratios. For the homemade flow cell, a detection potential of 1.1 V was chosen because MG and LMG exhibited a steady response. The flow analysis results showed linear concentration ranges of 1-100 microM and 4-80 microM for MG and LMG, respectively. The detection limit for both compounds was 50 nM.

Fluorometric assay of tiopronin based on inhibition of multienzyme redox system

In this paper, a simple and sensitive fluorimetric method for the determination of tiopronin (N-(2-mercaptopropionyl)-glycine) is proposed. The method is based on the strong inhibitory effect of tiopronin on the multienzyme redox system of hemoglobin, nicotinamide adenine dinucleotide (NADH) and H(2)O(2), in which the intrinsic fluorescence of NADH was employed as the detection signal. The calibration graph is linear in the range 6.13 x 10(-7) to 6.13 x 10(-6) M with a detection limit of 1.65 x 10(-7) M and the relative standard deviation of 2.02%. Kinetics in the pseudo-first-order conditions was investigated by stopped-flow spectrofluorometry and the inhibition mechanism of tiopronin was verified of the competitive type.

Electroanalysis of Tetracycline Using Nickel-implanted Boron-doped Diamond Thin Film Electrode Applied to Flow Injection System

The electrochemical analysis of tetracycline was investigated using nickel-implanted boron-doped diamond thin film electrode by cyclic voltammetry and amperometry with a flow injection system. Cyclic voltammetry was used to study the electrochemical oxidation of tetracycline. Comparison experiments were carried out using as-deposited boron-doped diamond thin film electrode (BDD). Nickel-implanted boron-doped diamond thin film electrode (Ni-DIA) provided well-resolved oxidation irreversible cyclic voltammograms. The current signals were higher than those obtained using the as-deposited BDD electrode. Results using nickel-implanted boron-doped diamond thin film electrode in flow injection system coupled with amperometric detection are presented. The optimum potential for tetracycline was 1.55 V versus Ag/AgCl. The linear range of 1.0 to 100 microM and the detection limit of 10 nM were obtained. In addition, the application for drug formulation was also investigated.