Analytica Chimica Acta 514 (2004) 211–218 Simultaneous spectrophotometric determination of Vitamin K 3 and 1,4-naphthoquinone after cloud point extraction by using genetic algorithm based wavelength selection-partial least squares regression Hamid Abdollahi ∗ , Leila Bagheri Department of Chemistry, Institute for Advanced Studies in Basic Sciences, Zanjan 45195-159, Iran Received 27 October 2003; received in revised form 8 March 2004; accepted 16 March 2004 Abstract Cloud point extraction has been used for the preconcentration of Vitamin K 3 and 1,4-naphthoquinone, after their reaction by aniline, and later simultaneous spectrophotometric analysis by genetic algorithm-partial least squares (GA-PLS) calibration using octylphenoxy- polyethoxyethanol (Triton X-114) as surfactant. The chemical variables affecting the analytical performance of the methodology were studied and optimized. Under the optimum conditions [i.e., [aniline] = 0.033 M, [Triton X-114] = 0.22% (w/v), equilibration time 15 min and cloud point 25 ◦ C], preconcentration of 15 ml of sample solution permitted the detection of 0.05 and 0.08 g ml -1 for Vitamin K 3 and 1,4-naphtaquinone, respectively. The predictive abilities of partial least squares regression (PLS), genetic algorithm-partial least squares regression, iterative target transformation factor analysis (ITTFA) and principal components-artificial neural networks (PC-ANN) were ex- amined for simultaneous determination of two quinines. The GA-PLS shows superiority over other applied multivariate methods due to the wavelength selection in PLS calibration using a genetic algorithm without loss of prediction capacity, provides useful information about the chemical system. © 2004 Elsevier B.V. All rights reserved. Keywords: Cloud point extraction; GA-PLS; Vitamin K 3 ; 1,4-Naphthoquinone 1. Introduction Surfactants are a special type of analytical reagent which provide excellent improvement in almost every area of chemistry [1]. The possibility of forming microheteroge- neous structures in solution, namely micelles, gives rise to perhaps the most important characteristic, that is the ability to solubilize otherwise water-insoluble molecules in what is essentially an aqueous matrix. It has been demonstrated that the surfactant solutions pro- vide a reaction medium, able to modify reaction rate, equi- librium position, product obtained and spectral or analytical parameters. It is also possible to enhance sensitivity of chro- matic reactions and avoid undesired lateral reaction [2,3]. The analytical potential of micellar systems can be further increased due to the fact that non-ionic isotropic micellar solution are separated into two phases, when a certain tem- ∗ Corresponding author. Tel.: +98-2414152162; fax: +98-2414249023. E-mail address: abd@iasbs.ac.ir (H. Abdollahi). perature called cloud point is reached [4,5]. The separated phases include a surfactant-rich phase and a bulk aqueous phase. The hydrophobic solutes can be enriched into the surfactant-rich phase. The small volume of surfactant-rich phase obtained with this methodology permits the design of extraction schemes that are simple and cheap, and have lower toxicity than extraction with organic solvents. They can pro- vide results comparable to those obtained by other separa- tion techniques. The comprehensive reviews of the theory and applications of surfactant-mediated separation in analyt- ical chemistry are available [4,6]. Although many successful applications have been reported, several workers agree that these complex systems require a great deal of fundamental research [7]. Quinones are compounds of wide occurrence in nature, their importance in biochemistry as bacteriostatic [8], anti- fungicidal action [9], in the inhibitory influence on certain enzymes like carboxylase and urease [8], the antitumor activ- ity, which makes some quinones useful in cancer chemother- apy [10]. In addition the role of Vitamin K in blood clot- 0003-2670/$ – see front matter © 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.aca.2004.03.048