Analytica Chimica Acta 507 (2004) 247–253 Analysis of amino acids in complex samples by using voltammetry and multivariate calibration methods Laura Moreno a , Arben Merkoçi a , Salvador Alegret a , Santiago Hernández-Cassou b , Javier Saurina b,∗ a Sensors and Biosensors Group, Department of Chemistry, Autonomous University of Barcelona, 08193 Bellaterra, Barcelona, Spain b Department of Analytical Chemistry, University of Barcelona, Diagonal 647, Barcelona-08028, Spain Received 23 May 2003; received in revised form 28 October 2003; accepted 12 November 2003 Abstract A voltammetric method is proposed for the simultaneous determination of tryptophan, cysteine, and tyrosine using multivariate calibration techniques. Various electrodes and voltammetric techniques were explored to ascertain the optimum measurement strategy. Among them, differential pulse voltammetry (DPV) with a Pt electrode was selected as analytical technique since it provided a suitable compromise between sensitivity and reproducibility while allowing the oxidation peaks of the three compounds to be reasonably discriminated. The sensitivity of DPV with Pt electrode for Trp standards was 8.4 × 10 -2 A l mol -1 , the repeatability 3.7% and the detection limit below 10 -7 M. The lack of full selectivity of the voltammetric data was overcome using multivariate calibration methods on the basis of the differences in the voltammetric waves of each compound. The accuracy of predictions was evaluated preliminarily from the analysis of three-component synthetic mixtures. Subsequently, this method was applied to the analysis of oxidizable amino acids in feed samples. Results obtained were in good concordance with those given by the standard method using an amino acid analyzer. © 2003 Elsevier B.V. All rights reserved. Keywords: Oxidizable amino acids; Differential pulse voltammetry; Multivariate calibration; Partial least square regression 1. Introduction The analysis of amino acids is commonly based on liquid chromatography [1,2] and capillary electrophoresis [3,4] with pre- or post-column labeling and spectroscopic detection of the corresponding derivatives. However, the electrochemical detection in combination with separation techniques (HPLC–ED) [5–8] cannot be overlooked as addi- tional advantages may be gained. In this case, a highly sen- sitive and direct detection of analytes can be accomplished without needing any derivatization. Nowadays, simpler and faster procedures are needed to satisfy the great demand of amino acid determinations in fields such as food process- ing, biochemistry, pharmaceuticals, and clinical analysis. Voltammetric methods may be an interesting alternative to separation techniques for the analysis of oxidizable amino ∗ Corresponding author. Tel.: +34-934-034-445; fax: +34-934-021-233. E-mail address: xavi@apolo.qui.ub.es (J. Saurina). acids on the basis of the inherent electroactivity of thiol or aromatic groups [9–14]. For these applications, traditional electrode materials such as carbon, platinum and gold are commonly used, although significant improvements can be achieved by using modified electrodes [15–17]. For instance, the development of new copper-metal alloy electrodes opens up the possibility of a sensitive detection of a wider variety of amino acids since their electrocatalitic activity [18,19]. The main disadvantage of voltammetric detection is its rather complex response in comparison with spectroscopy. For this reason, extracting qualitative and quantitative infor- mation from electrochemical data may result in a difficult task. However, the data analysis can be facilitated greatly by using chemometric techniques which permit the relevant information to be recovered [20,21]. The study of electroanalytical data by means of chemo- metrics is a new research trend which has attracted the in- terest of analytical chemists. Although the possibilities of this combination have been little explored to date because of the data complexity, in some cases multivariate techniques 0003-2670/$ – see front matter © 2003 Elsevier B.V. All rights reserved. doi:10.1016/j.aca.2003.11.048