Suchada Chuanuwatanakul

Electroanalysis of sulfonamides by flow injection system/high-performance liquid chromatography coupled with amperometric detection using boron-doped diamond electrode☆

Sulfonamides (SAs) were electrochemically investigated using cyclic voltammetry at a boron-doped diamond (BDD) electrode. Comparison experiments were carried out using a glassy carbon electrode. The BDD electrode provided well-resolved oxidation, irreversible cyclic voltammograms and higher current signals when compared to the glassy carbon electrode. Results obtained from using the BDD electrode in a flow injection system coupled with amperometric detection were illustrated. The optimum potential from a hydrodynamic voltammogram was found to be 1100mV versus Ag/AgCl, which was chosen for the HPLC-amperometric system. Excellent results of linear range and detection limit were obtained. This method was also used for determination of sulfonamides in egg samples. The standard solutions of 5, 10, and 15ppm were spiked in a real sample, and percentage of recoveries was found to be between 90.0 and 107.7.

Graphene-carbon paste electrode for cadmium and lead ion monitoring in a flow-based system

An environment friendly electrode for determining Cd(2+) and Pb(2+) levels in an automated flow system was successfully developed. Cyclic voltammetry and square wave anodic stripping voltammetry (SWASV) coupled with sequential injection analysis (SIA) were employed to study the electrochemical behavior of the electrode. The in situ bismuth-modified graphene-carbon paste electrode (Bi-GCPE) exhibited excellent electrooxidation of Cd(2+) and Pb(2+) in the automated flow system with a significantly higher peak current for both metal ions compared with the unmodified CPE. The limits of detection from this method were 0.07 and 0.04 μg L(-1) for Cd(2+) and Pb(2+), respectively, with a linear oxidation peak current response for Cd(2+) and Pb(2+) in the range of 0.10-50.0 μg L(-1) under optimum conditions. The Bi-GCPE was also applied for the determination of Cd(2+) and Pb(2+) in low- (tap water) and high- (sea bass fish and undulated surf clam tissues) matrix complexity samples by automated flow system. The recoveries were acceptable and ranged from 70.4% to 120% for Cd(2+) and 65.8% to 113.5% for Pb(2+).

On-line preconcentration and determination of lead and cadmium by sequential injection/anodic stripping voltammetry

The highly sensitive determination of lead (Pb(II)) and cadmium (Cd(II)) ions, with a limit of detection of 0.01μgL(-1) for Pb(II) and Cd(II), by on-line preconcentration and anodic stripping voltammetry (ASV) controlled by a sequential injection analysis (SIA) system is reported here. The SIA system consisted of a syringe pump, an 8-port selection valve and a 6-port switching valve and was incorporated with a bismuth coated screen-printed carbon nanotube electrode (Bi-SPCNTE). The preconcentration of metal ions was performed by solid phase extraction using an Analig TE-05 chelating resin mini-column on a switching valve. The metal ions collected were then eluted from the resin with 1M hydrochloric acid (HCl), deposited on the electrode surface at -1.3V vs. Ag/AgCl and then measured with ASV. The pH of the sample, eluent volume, flow rate, concentration of the bismuth plating solution and the square-wave voltammetric parameters were optimized. Under the optimum conditions, an enrichment factor of 11.9-fold and 6.6-fold for Pb(II) and Cd(II) ions, respectively, was attained. Detection of Pb(II) and Cd(II) had two different linear ranges (0.5-15μgL(-1) and 15-70μgL(-1)).

Use of nickel implanted boron-doped diamond thin film electrode coupled to HPLC system for the determination of tetracyclines ☆

The electrochemical analysis of tetracyclines was investigated using nickel-implanted boron-doped diamond thin film electrode (Ni-DIA) by cyclic voltammetry and high performance liquid chromatographic with amperometry. Cyclic voltammetry was used to study the electrochemical oxidation of tetracyclines. Comparison experiments were carried out utilizing as-deposited BDD and glassy carbon electrodes. Ni-DIA electrode provided well-resolved oxidative irreversible cyclic voltammograms and the highest current signals among the electrode studied. High performance liquid chromatography (HPLC) with amperometric detection was also studied. The chromatography was performed using a commercially available Inertsil C18 column, with the mobile phase being: 80% phosphate buffer (pH 2.5)-20% acetonitrile and detected at 1.55V. The methods were validated over the concentration range 0.05-100ppm with the overall average recoveries from 83.3 to 102.5% and R.S.D. of less than 10%. The proposed method was further applied to analyse shrimp samples.

Method development for the determination of arsenic by sequential injection/anodic stripping voltammetry using long-lasting gold-modified screen-printed carbon electrode

An automated method has been developed for determining the concentration of inorganic arsenic. The technique uses sequential injection/anodic stripping voltammetry with a long-lasting gold-modified screen-printed carbon electrode. The long-lasting gold electrode was electrochemically deposited onto a screen-printed carbon electrode at a potential of -0.5 V vs. Ag/AgCl in a supporting electrolyte solution of 1M hydrochloric acid. Under optimal conditions and the applied potentials, the electrode demonstrated that it can be used for a long time without a renewal process. The linear range for the determination of arsenic(III) was 1-100 μg L(-1), and the limit of detection (LOD) in standard solutions was as low as 0.03 μg L(-1) for a deposition time of 120 s and sample volume of 1 mL. This method was used to determine the concentration of arsenic(III) in water samples with satisfactory results. The LOD in real samples was found to be 0.5 μg L(-1). In addition, speciation between arsenic(III) and arsenic(V) has been achieved with the proposed method using deposition potentials of -0.5 V and -1.5 V for the determination of the arsenic(III) concentration and the total arsenic concentration, respectively; the results were acceptable. The proposed method is an automated system that offers a less expensive alternative for determining trace amounts of inorganic arsenic.

Polyaniline/graphene quantum dot-modified screen-printed carbon electrode for the rapid determination of Cr(VI) using stopped-flow analysis coupled with voltammetric technique.

Polyaniline/graphene quantum dots (PANI/GQDs) were used to modify a screen-printed carbon electrode (SPCE) in a flow-based system. A method for rapidly determining the Cr(VI) concentrations by using stopped-flow analysis has been developed using an Auto-Pret system coupled with linear-sweep voltammetry using the PANI/GQD-modified SPCE. The GQDs, synthesized in a botton-up manner from citric acid, were mixed with aniline monomer in an optimized ratio. The mixture was injected into an electrochemical flow cell in which electro-polymerization of the aniline monomer occurred. Under conditions optimized for determining Cr(VI), wide linearity was obtained in the range of 0.1-10 mg L(-1), with a detection limit of 0.097 mg L(-1). For a sample volume of 0.5 m L, the modified SPCE can be used continuously with a sample-throughput of more than 90 samples per hour. In addition, this proposed method was successfully applied to mineral water samples with acceptable accuracy, and the quantitative agreement was accomplished in deteriorated Cr-plating solutions with a standard traditional method for Cr(VI) detection.

Voltammetric detection of carbofuran determination using screen-printed carbon electrodes modified with gold nanoparticles and graphene oxide

Carbofuran is a highly toxic pesticide that is heavily used in agriculture due to its high effectiveness and low cost. Improved methods that are simpler and lower cost are needed for carbofuran detection in food and agricultural samples. Herein, we describe the development of a unique electrochemical method for carbofuran-phenol, which is the main hydrolysis product of carbofuran. We have successfully developed a highly accurate and precise method in a portable size using a screen-printed carbon electrode (SPCE) that is modified with graphene oxide (GO) and gold nanoparticles (AuNPs). Consequently, the developed electrode is highly sensitive to and selective for carbofuran. Using the central composite design (CCD) approach, we optimized the method for analysis parameters including the electrode surface loadings of GO and AuNPs as well as the working solution pH. The method exhibited a wide linear range of 1-250µM for analyte detection using differential pulse voltammetry (DPV) on AuNPs/GO-SPCE under the optimized conditions. The limits of detection and quantitation were 0.22 and 0.72µM, respectively. In addition, we also report the application of the method for carbofuran determination in real cucumber and rice samples. This sensitive and selective carbofuran detection method is very promising for simple and low cost analysis in real agricultural fields.

Determination of nickel(II) by ion-transfer to hydroxide medium using sequential injection-electrochemical analysis (SIECA)

A method for the determination of Ni(II) using ion-transfer to a hydroxide medium has been developed by the sequential injection-electrochemical analysis (SIECA), a combination between an automated flow-based analysis and electrochemical techniques with a homemade screen-printed carbon electrode (SPCE). A sample/standard solution was introduced into an electrochemical flow cell where the Ni(II) in the solution was electrochemically reduced and accumulated on the SPCE. The accumulated Ni was then oxidized to Ni(II) in a hydroxide medium, which led to the formation of nickel hydroxide (Ni(OH)2) and nickel oxyhydroxide (NiOOH) on the SPCE. The electrochemical response associated with Ni(OH)2 and NiOOH was subsequently determined by square-wave voltammetry to account for Ni(II). Under optimal conditions, the proposed method provides a low detection limit of 0.02mgmL-1. This method was further applied to determine the Ni(II) content of standard-spiked mineral water samples with satisfactory results.