Year

1998

Degree Name

Doctor of Philosophy

Department

Department of Chemistry

Abstract

A generic electrochemical sensing system for ion chromatography has been developed. The system comprised of a number of hardware and software components. These included photolithographically produced, microelectrodes coated with conducting electroactive polymer (CEP) as sensing elements, with multichannel data acquisition, signal processing and data analysis elements. This system was applied to pulsed amperometric detection of a range of anions and cations after their separation by ion chromatography. In conjunction with chemometric data analysis, the problem of potassium (K) and methylamine (MA) peak integrity was addressed. In the course of this work, the sensor array was effectively tuned by the principal components analysis (PCA) of K and M A flow injection analysis (FIA) data. In this way, the optimal chemical and electrochemical detection parameters were identifíed as being: PP/Cl, PP/MSA, PP/PSS (between switching potentials of-0.75V and -0.25V vs Ag/AgCI reference electrode), PP/DS and PP/Tir (between switching potentials of-0.95V and -0.45V vs Ag/AgCI reference electrode).

Analysis of score and biplots generated by the PCA of CV data represents a fast and experimentally simpler method of tuning sensor selectivity. This was a novel treatment of C V data and certainly the first reported for the identification of pulsed detection parameters for FIA. This method produced results which were in agreement with those obtained with the FIA data.

The optimised array, in conjunction with partial least squares (PLS) regression analysis, was able to discriminate between purê and impure K and MA peaks of up to 5 % MA impurity in K or to 20% K impurity in MA . Through this work, the flexibility offered to the system by post-acquisition data manipulation was demonstrated. The use of current responses gathered over whole pulses rather than discrete current sample points was shown to be an effective strategy in this application.

The analytical performance of the CEP sensors to a range of electroinactive anions and cations did not compare favourably to conductivity detection. Calibration curves revealed that the CEP sensors are subject to polymer "saturation" effects, in that the analytical signal did not increase indefínitely with analyte concentration. This, along with sensitivity data for polymers and conductivity detection, was evidence that the C E P responses were not dominated by the change in solution conductivity.

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