Development of instrumentation for amperometric and coulometric detection using ultramicroelectrodes

Abstract

Neste trabalho é apresentado o desenvolvimento de uma instrumentação simples, portátil e de baixo custo para detecção amperométrica e coulométrica usando ultramicroeletrodos em diferentes sistemas analíticos. O programa, desenvolvido em LabVIEW 7.1 TM , é capaz de realizar três modos de detecção (amperométrico, coulométrico e amperométrico pulsado) e voltametria cíclica. A instrumentação desenvolvida foi avaliada utilizando os seguintes sistemas: voltametria cíclica de eletrodos metálicos em solução alcalina, detecção eletroquímica em fluxo de glicose e glicina, e também na determinação direta do herbicida glifosato (detecção eletroquímica aliada à cromatografia líquida de alta eficiência, CLAE).In this work it is presented the development of a simple, portable and inexpensive instrumentation for amperometric and coulometric detection in different analytical instrumentation systems utilizing ultramicroelectrodes. The software, developed in LabVIEW 7.1 TM , is capable to carry out three main detection techniques (amperometric, pulsed amperometric and coulometric detection) and a voltammetric technique (cyclic voltammetry). The instrumentation was successfully evaluated using the following systems: cyclic voltammograms of metallic electrodes in alkaline solutions, flow electrochemical detection of glucose and glycine and direct determination of herbicide glyphosate (electrochemical detection coupled to HPLC). Keywords: instrumentation, portable, electrochemical detection, ultramicroelectrodes, flow system IntroductionAmperometry has become a widely used detection method for a variety of analytical techniques including flow injection analysis (FIA), high-performance liquid chromatography (HPLC), capillary liquid chromatography (cLC) and capillary electrophoresis (CE).1,2 Its popularity stems from a combination of sensitivity, selectivity, and versatility.3 Amperometric detection is usually performed at a solid electrode under constant applied potential, which is typically denoted as dc amperometry.Nowadays, constant potential amperometric detection of many compounds has been successfully accomplish using glassy carbon, Cu, Ni, Co, and others non-noble metal electrodes. 4 Numerous aromatic compounds (e.g., phenols, aminophenols, catecholamines, and other metabolic amines) are easily detected by anodic reactions in dc amperometry utilizing these electrodes. Electronic resonance in the aromatic compounds functions to stabilize the free-radical intermediate products of anodic oxidations and as a consequence, the activation barrier for electrochemical reaction is lowered significantly. 5However, although the high electroactivity of the aromatic compounds in the glassy carbon electrode, it does not J. Braz. Chem. Soc. 132 Development of Instrumentation for Amperometric and Coulometric Detection enable the oxidation of some polar aliphatic compounds (e.g., carbohydrates, amines and alcohols). This is due the lack of a stabilization process of the free-radial intermediate products of the anodic oxidation these compounds...

Analytical chemistry in Brazil: healthy and growing

“…Ultramicroelectrodes for detection by coulometry or amperometry in flowing systems were also developed. 291 The applicability was demonstrated by measurement of glucose and glycine in a flow-based system and of glyphosate, coupling the detector to a HPLC system.…”