Flow Injection Electrochemical Quartz Microbalance with ICP-OES Detection

Abstract

The electrochemical quartz crystal microbalance (EQCM) has been previously reported in flow injection (FI) mode as a microgravimetric sensor for analytes that can be deposited onto an electrode surface through various mechanisms such as adsorption, covalent bond, or electrodeposition. Since this methodology does not provide the composition of the deposited species, it must be coupled with other analytical techniques.In this work, a new hyphenated technique, flow injection – electrochemical quartz crystal microbalance – inductively coupled plasma optical emission spectroscopy (FI-EQCM-ICP-OES), is used to study the deposition and stripping of metallic ions under hydrodynamic conditions in a modified commercially-available EQCM flow cell with a reaction volume of 50 uL. An automatic flow injection valve (FIV) delivers a fixed volume of analyte from a sample loop to the EQCM flow cell, where the electrodeposition reaction occurs, and the current and frequency change corresponding to the mass deposited on the electrode is measured in real time. After a film of the analyte has formed it can be rapidly stripped by changing the potential of the electrode. An ICP-OES connected downstream of the EQCM provides continuous elemental analysis throughout the deposition and stripping processes. One of the advantages is the possibility of sequential deposition-stripping experiments without having to disturb the working electrode in the flow cell.This platform was tested via flow injection of cupric sulfate samples in a sulfuric acid matrix at 200 uL/min, with cathodic electrodeposition and anodic stripping performed at different potentials. We also developed a finite element 3D model of the electrochemical flow cell in COMSOL Multiphysics®, with the simulated results in reasonable agreement to the measured current and mass deposition in the copper experiments. The image below shows the simulated [Cu+2] profile in COMSOL Multiphysics® during cathodic electrodeposition, 62 seconds after the sample enters the reaction chamber of the flow cell. Figure 1