Flow-Injection Amperometric Method for Indirect Determination of Dopamine in the Presence of a Large Excess of Ascorbic Acid

Reusable graphite-based electrochemical sensors for L-dopa and dopamine detection

A fully reusable electrochemical device is proposed for the first time made from laser cutting and a homemade conductive ink composed of carbon and nail polish. As a sensor substrate, we applied polymethyl methacrylate, which allows the surface to be renewed by simply removing and reapplying a new layer of ink. In addition to the ease of renewing the sensor's conductive surface, the design of the device has allowed for the integration of different forms of analysis. The determination of L-Dopa was performed using DPV, which presented a linear response range between 5.0 and 1000.0 μmol L-1, and a LOD of 0.11 μmol L-1. For dopamine, a flow injection analysis system was employed, and using the amperometric technique measurements were performed with a linear ranging from 2.0 to 100.0 μmol L-1 and a LOD of 0.26 μmol L-1. To demonstrate its applicability, the device was used in the quantification of analytes in pharmaceutical drug and synthetic urine samples.

Simultaneous detection of dopamine and ascorbic acid by using a thread-based microfluidic device and multiple pulse amperometry

This study presents a novel approach for the simultaneous detection of ascorbic acid (AA) and dopamine (DA) using an affordable and user-friendly microfluidic device. Microfluidic devices, when combined with electrochemical detectors like screen-printed electrodes (SPEs), offer numerous advantages such as portability, high sample throughput, and low reagent consumption. In this study, a 3D-printed microfluidic device called a μTED was developed, utilizing textile threads as microfluidic channels and an unmodified SPE as the amperometric detector. The method employed multiple pulse amperometry (MPA) with carefully selected potential values (+0.65 V and -0.10 V). The reduction current signals generated by dopamine o-quinone were used to calculate a correction factor for the oxidation signals of ascorbic acid, enabling simultaneous quantification. The developed microfluidic device ensured a stable flow rate of the carrier solution at 1.19 μL s-1, minimizing the consumption of samples and reagents (injection volume of 2.0 μL). Under the optimized experimental conditions, a linear range from 50 to 900 μmol L-1 was achieved for both DA and AA. The obtained sensitivities were 2.24 μA L mmol-1 for AA and 5.09 μA L mmol-1 for DA, with corresponding limits of detection (LOD) of 2.60 μmol L-1 and 1.54 μmol L-1, respectively. To confirm the effectiveness of the proposed method, it was successfully applied to analyze AA and DA in a commercial blood serum sample spiked at three different concentration levels, with a medium recovery rate of 70%. Furthermore, the MPA technique demonstrated its simplicity by enabling the simultaneous determination of AA and DA without the need for prior separation steps or the use of chemically modified electrodes.

Halochromic Polystyrene Nanofibers Obtained by Solution Blow Spinning for Wine pH Sensing

Colorimetric sensors developed by the solution blow spinning (SBS) technique have a rapid response to a variation in different physicochemical properties. In this study, polystyrene nanofibrous (PSNF) mats containing the bromothymol blue (BTB) indicator were obtained by SBS for the pH sensing of wine sample. The incorporation of the indicator did not promote changes in fiber diameter but led to the appearance of beads, allowing for the encapsulation of BTB. The halochromic property of BTB was retained in the PSNF material, and the migration tests showed that the indicator mats presented values below the maximum acceptable limit (10 mg dm-2) established by EU Commission Regulation No. 10/2011 for foods with an alcohol content up to 20%. The present study opens the possibility of applying nanostructured materials to innovative food packaging which, through nanosensory zones, change color as a function of the food pH.

Two new electrochemical methods for fast and simultaneous determination of codeine and diclofenac

In this paper, we present two new electrochemical methods for fast and simultaneous determination of codeine (CO) and diclofenac (DCF). The first one is based on batch injection analysis with amperometric detection (BIA-MPA) and the second one is based on capillary electrophoresis with capacitively coupled contactless conductivity detection (CE-C(4)D). The proposed BIA-MPA method is highly-precise (RSD of 1.1% and 0.9% for DCF and CO, respectively; n=10), fast (300 injections h(-1)) and has low detection limits (1.1 and 1.0 µmol L(-1) for DCF and CO, respectively). The proposed CE-C(4)D method allows the determination of CO and DFC in less than 1 min with high precision (RSD of 0.3% and 0.7% for DCF and CO, respectively; n=10) and low detection limits (11 and 21 µmol L(-1) for DCF and CO, respectively). Both proposed methods were applied to the determination of CO and DCF in pharmaceutical samples with similar results to those achieved by high-performance liquid chromatography (HPLC) at a 95% confidence level.

Direct amperometric determination of tert-butylhydroquinone in biodiesel

The direct amperometric determination of tert-butylhydroquinone (TBHQ) in biodiesel at an unmodified glassy carbon electrode is reported. A biodiesel aliquot was added into an electrochemical cell containing a 75% (v/v) ethanol-water solution under stirring (with final concentration of 50 mmol L(-1) HClO(4)). The amperometric method involved the continuous application of three sequential potential pulses to the working electrode (700 mV for 300 ms, 0 mV for 100 ms and -50 mV for 1s). TBHQ was continuously monitored at the first (direct oxidation) and optionally at the second (reduction) potential pulse while the third potential pulse was applied for cleaning of the electrode surface. For comparison, the samples were also analyzed by high-performance liquid-chromatography and a good agreement between the results was verified. Recovery values for spiked samples were between 90% and 95% and the reproducibility of the proposed method was around 5% (n=5). The proposed method can be easily adapted for on-site analysis.