Voltammetric detection of vitamin B1 (thiamine) in neutral solution at a glassy carbon electrode:Via in situ pH modulation

Voltammetric analysis is often dependent on pH and on the addition of buffer reagents to optimise the analytical procedure. This approach is not always possible for in situ analytical measurements, for example when studying biological fluids or ingredients in food. Therefore, a method is proposed herein, which employs a working electrode to do both, that is, to locally modulate the pH value and to measure the analytical response. As a model system, thiamine (vitamin B1) is detected in aqueous KCl with a pH modulation brought about with negative potentials applied to the working electrode. Interferences from ascorbic acid and uric acid are considered. Exploratory data are presented and methods for improving the detection limit are suggested. Their potential for applications in electroanalysis (and in a broader range of processes) is discussed and the detection of thiamine in rice is demonstrated.</p

Development of Differential Pulse Anodic Stripping Voltammetry Technique for Cadmium(II) Detection and Its Application in Water Spinach

Cadmium is a toxic pollutant that is harmful to the environment and humans. The purpose of this research was to develop a method for cadmium(II) detection using differential pulse anodic stripping voltammetry (DPASV) using a glassy carbon electrode. The developed method was then applied for cadmium detection in the vegetable samples which is water spinach. The developed method was optimized in several parameters such as potential window, deposition potential, deposition time, and scan rate. The developed method for cadmium(II) detection was also investigated in its analytical performance includes linearity, precision, detection limit, and quantitation limit. The optimum conditions for cadmium(II) detection in 0.1 M KCl using DPASV technique obtained such as potential window from -1200 to -100 mV, deposition potential of -1100 mV (vs Ag/AgCl), and deposition time of 360 s. It was obtained good linearity for cadmium(II) detection using the DPASV technique with an&nbsp;R2 of 0.996. The precision was expressed as %SBR with 0.66%. The detection and quantitation limits for cadmium(II) detection were 0.4206 µM~0.0771 ppm and 0.5525 µM~0.1013 ppm, respectively. The developed method was then applied for cadmium(II) measurement in the water spinach sample and the obtained cadmium(II) concentration in water spinach was 0.2399 mg/Kg

CARBON PASTE ELECTRODE HEXADECYLTRIMETHYLAMMONIUM BROMIDE MODIFIED NATURAL ZEOLITE FOR CHROMIUM(VI) DETECTION

A simple voltammetric technique for quantification of chromium(VI) is presented in this work. The technique is based on linear sweep voltammetric reduction Cr(VI) on hexadecyltrimethylammonium bromide (HDTMABr) modified Lampung zeolite carbon paste electrode. Selected HDTMABr concentration for natural zeolite modification is obtained 200 mM. Working electrode for chromium(VI) detection is made by graphite, paraffin oil and HDTMABr modified Lampung zeolite. The effect of supporting electrolyte matrix, pH and also scan rate is also investigated. The calibration curve for chromium(VI) detection using the proposed method shows linearity from 0.2 to 1.0 mM with sensitivity, detection and quantification limit, and precision was 0.4294 mM, 3.63 x 10-4 mM, 1.197 x 10-3 mM, 4.49%, respectively

A Brief Review on Fabrication of Screen-Printed Carbon Electrode: Materials and Techniques

Screen-printed carbon electrode (SPCE) is one of the most interesting designs to combine a working (from carbon based material), reference, and counter electrode in a single-printed substrate. SPCE has been used in many electrochemical measurements due to its advantages for analysis in microscale. This paper summarises the main information about SPCE fabrication from the material and fabrication technique aspect on the flat substrate based on the work that has been published in the last 30 years. The success of SPCE fabrication is highly dependent on the composition of conductive ink which consists of conductive materials, binder, and solvents; substrate; and fabrication techniques. Among the carbon-based materials, the most widely used for SPCE fabrications are graphite, graphene, and carbon nanotubes. The frequent binder used are polymer-based materials such as polystyrene, polyaniline, poly 3,4-ethylenedioxythiophene:polystyrene sulfonate (PEDOT:PSS), and polyvinyl chloride. The solvents used for SPCE fabrication are varied including water and various organic solvents. The main characteristics of the SPCE substrate should be inert in order to avoid any interferences during electrochemical measurements. The screen printing and inkjet printing technique are preferred for SPCE fabrication due to easy fabrication and the possibility for mass production of SPCE

Cationic diodes by hot-pressing of Fumasep FKS-30 ionomer film onto a microhole in polyethylene terephthalate (PET)

A cationic diode is fabricated by hot-pressing a commercial cation-conducting ionomer membrane (Fumasep FKS-30) onto a polyethylene terephthalate (PET) substrate with microhole of 5, 10, 20, or 40 mu m diameter. Both, symmetric (ionomer on both sides) and asymmetric (ionomer only on the working electrode side) cases are investigated in a 4-electrode measurement cell. A 5-electrode measurement cell in generator-collector mode is employed to directly detect competing proton transport through the ionomer. Only the asymmetric device allows ion current rectification to be observed. With decreasing microhole diameter the rectification effect increases. With increasing electrolyte concentration (for aqueous HCl, NaCl, LiCl, NH4Cl, MgCl2, CaCl2) the rectification effect diminishes. Competition between cation transport and proton transport is observed in all cases. A qualitative impedance model is developed to diagnose the quality and performance of these cationic diodes.</p

Ionic Diode Characteristics at a Polymer of Intrinsic Microporosity (PIM) | Nafion “Heterojunction” Deposit on a Microhole Poly(ethylene-terephthalate) Substrate

Ionic diode phenomena occur at asymmetric ionomer | aqueous electrolyte microhole interfaces. Depending on the applied potential, either an “open” or a “closed” diode state is observed switching between a high ion flow rate and a low ion flow rate. Physically, the “open” state is associated mainly with conductivity towards the microhole within the ionomer layer and the “closed” state is dominated by restricted diffusion-migration access to the microhole interface opposite to the ionomer. In this report we explore a “heterojunction” based on an asymmetric polymer of intrinsic microporosity (PIM) | Nafion ionomer microhole interface. Improved diode characteristics and current rectification are observed in aqueous NaCl. The effects of creating the PIM | Nafion micro-interface are investigated and suggested to lead to novel sensor architectures