Resolution of amino acid mixtures by an array of potentiometric sensors based on boronic acid derivative in a SIA flow system

The objective of this work was to perform the quantitative analysis of 4 amino acids mixtures: phenylalanine, tyrosine, ornithine and glutamic acid. For this purpose a potentiometric sensor array (electronic tongue) and Sequential Injection Analysis (SIA) measurement system were employed. The flow-through sensor array was composed of 6 miniaturized classical ion-selective electrodes based on polymeric membranes (plasticized PVC) containing 4-octyloxyphenylboronic acid as an ionophore and/or an ion exchanger. Partial Least Squares (PLS) analysis of the steady-state sensor array responses, measured in amino acids mixtures prepared by the SIA system (in two buffer solutions), permitted a correct quantitative analysis only of glutamic acid and ornithine. While a further chemometric treatment, involving the extraction of dynamic components of the transient response employing the Wavelet transform, the removal of less-significant coefficients by means of Causal Index pruning and training of an Artificial Neural Network (ANN) with the selected coefficients, allowed the simultaneous determination of the four amino acids.