Analytica Chimica Acta 666 (2010) 55–61 Contents lists available at ScienceDirect Analytica Chimica Acta journal homepage: www.elsevier.com/locate/aca A novel dual-valve sequential injection manifold (DV-SIA) for automated liquid–liquid extraction. Application for the determination of picric acid Jana ˇ Skrlíková a,∗ , Vasil Andruch a,∗ , Hana Sklenᡠrová b,∗ , Petr Chocholouˇ s b , Petr Solich b , Ioseph S. Balogh c a Department of Analytical Chemistry, University of P.J. ˇ Safárik, SK-04154 Koˇ sice, Slovak Republic b Department of Analytical Chemistry, Faculty of Pharmacy, Charles University, CZ-50005 Hradec Králové, Czech Republic c Department of Chemistry, College of Nyíregyháza, HU-4400 Nyíregyháza, Hungary article info Article history: Received 8 January 2010 Received in revised form 10 March 2010 Accepted 18 March 2010 Available online 1 April 2010 Keywords: Sequential injection analysis Dual-valve system Liquid–liquid extraction Picric acid abstract A novel dual-valve sequential injection system (DV-SIA) for online liquid–liquid extraction which resolves the main problems of LLE utilization in SIA has been designed. The main idea behind this new design was to construct an SIA system by connecting two independent units, one for aqueous–organic mixture flow and the second specifically for organic phase flow. As a result, the DV-SIA manifold consists of an Extraction unit and a Detection unit. Processing a mixture of aqueous–organic phase in the Extraction unit and a separated organic phase in the Detection unit solves the problems associated with the change of phases having dif- ferent affinities to the walls of the Teflon tubing used in the SI-system. The developed manifold is a simple, user-friendly and universal system built entirely from commercially available components. The system can be used for a variety of samples and organic solvents and is simple enough to be easily handled by oper- ators less familiar with flow systems. The efficiency of the DV-SIA system is demonstrated by the extrac- tion of picric acid in the form of an ion associate with 2-[2-(4-metoxy-fenylamino)-vinyl]-1,3,3-trimetyl- 3H-indolium reagent, with subsequent spectrophotometric detection. The suggested DV-SIA concept can be expected to stimulate new experiments in analytical laboratories and can be applied to the elaboration of procedures for the determination of other compounds extractable by organic solvents. It could thus form a basis for the design of simple, single-purpose commercial instruments used in LLE procedures. © 2010 Elsevier B.V. All rights reserved. 1. Introduction Liquid–liquid extraction (LLE) is a powerful, versatile separation technique still widely used for both the separation and precon- centration of a wide variety of analytes. Conventional, manually performed LLE has a number of serious limitations, since all sol- vents used are volatile, hazardous and even flammable in some cases. Many attempts have been made at overcoming these draw- backs in the LLE process. Several other separation techniques, called “miniaturized preconcentration methods based on liquid–liquid extraction” [1–4] and using only a small amount of organic solvent, have been described in recent years. Another potential method for avoiding the disadvantages of manual LLE is automation. Incorporating LLE into flow injection analysis (FIA) provides a number of advantages when compared with the manual procedure: a reduced consumption of hazardous ∗ Corresponding authors. E-mail addresses: jana.skrlikova@googlemail.com (J. ˇ Skrlíková), vasil.andruch@gmail.com (V. Andruch), Hana.Sklenarova@faf.cuni.cz (H. Sklenᡠrová). organic solvents, a decrease in the amount of human handling and thus less exposure to toxic vapours, as well as better reproducibility [5]. Numerous manifold configurations incorporating LLE into flow systems of differing complexity have been described in the lit- erature. Recently, Silvestre et al. provide a critical overview of existing arrangements and distinct extraction strategies, such as single extraction, multiple extractions, back-extraction, systems without phase separation and systems without phase segmenta- tion and separation [6]. Also, numerous reviews and monographs on this subject exist. Therefore, our aim was not to provide a com- plete overview of all existing LLE techniques in flow systems but only to list in this section those which are either important for our work or which represent interesting examples. Among the first articles dealing with this FIA-LLE system were those of Karlberg and Thelander [7] and Bergamin et al. [8]. Karl- berg and Thelander devised a system consisting of a pump, a rotary valve and a spectrophotometer. In their system, the organic phase divided the aqueous stream, which contained the sample, into small segments. The stream then passed through a Teflon coil in order to get the two phases into a regular pattern. The phases were then sep- arated, and the absorbance of the organic phase was measured. The 0003-2670/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.aca.2010.03.039