Analytical note Field-flow fractionation: An efficient approach for matrix removal of soil extract for inductively coupled plasma optical emission spectrometry Supharart Sangsawong, Weerawan Waiyawat, Juwadee Shiowatana, Atitaya Siripinyanond ⁎ Department of Chemistry and Center for Innovation in Chemistry, Faculty of Science, Mahidol University, Rama VI Rd., Bangkok 10400, Thailand abstract article info Article history: Received 27 August 2010 Accepted 26 April 2011 Available online 3 May 2011 Keywords: Field-flow fractionation Continuous-flow sequential extraction Inductively coupled plasma optical emission spectrometry Matrix removal Soil extract An on-line coupling between a continuous-flow sequential extraction (CFSE) unit and flow field-flow fractionation with cross flow matrix removal (FlFFF/CFM) with ICP-OES detection was developed for determination of metal leachability from soil. The use of high concentration of Mg(NO 3 ) 2 in exchangeable phase can cause undesirable matrix effects by shifting ionization equilibrium in the plasma, etc., resulting in a clear need for matrix removal. Therefore, the capability of FlFFF/CFM to remove Mg matrix ion from soil extract was evaluated. Poly(ethylene imine) (PEI) having molecular weight of 25,000 Da was added to form complexes with analyte elements (Cu, Mn, Pb, and Zn) but not the matrix element (Mg). The free Mg matrix ions were then removed by filtering off through the ultrafiltration membrane, having a 1000-Da molecular weight cut-off, inside the FlFFF channel. With the use of FlFFF/CFM, matrix removal efficiency was approximately 83.5%, which was equivalent to approximately 6-fold dilution of the matrix ion. The proposed hyphenated system of CFSE and FlFFF/CFM with ICP-OES detection was examined for its reliability by checking with SRM 2710 (a highly contaminated soil from Montana). The metal contents determined by the proposed method were not significantly different (at 95% confidence) from the certified values. © 2011 Elsevier B.V. All rights reserved. 1. Introduction The prediction of metal mobility and bioavailability has become important to evaluate their potential effects on the environment. This is often sought out by studying the leachability of metals by appropriate extractant [1,2] or using various solvents sequentially [3]. The chemical reagents used to perform sequential extraction are selected based on the goals pursued and on the physical character- istics of the sample [4]. These extractants include water to extract water soluble compartment, Mg(NO 3 ) 2 to extract exchangeable phase, acetic acid to extract acid soluble component, and hydroxyl ammonium chloride to target the reducible phase. Among these extractants, Mg(NO 3 ) 2 can cause severe matrix effect in inductively coupled plasma optical emission spectrometric (ICP-OES) detection [5] such as change in solution viscosity [6], shifting ionization equilibrium in the plasma [7] etc., and methods for matrix removal are thus needed. The use of ICP-OES to determine the extractable metal contents in soil has increased the productivity of the sequential extraction method and enabled a broader study of the geochemical association in soils [8]. Despite the advantage of ICP-OES as a suitable, multi-element technique, its principal disadvantage of low tolerance to high salt content can cause problems in many cases [9–11]. The extracting reagents used in sequential extraction schemes and soil matrices can cause spectral and non-spectral interferences. The former can be avoided by careful selection of the emission lines monitored. Nonethe- less, the latter is affected by many factors and causes signal suppression or enhancement. Therefore, non-spectral interferences require sample pretreatment to dilute or remove matrix elements from sample solutions before ICP-OES detection. Several approaches have been developed to overcome such interferences. Various approaches that were used to overcome matrix interference problems in ICP-MS, which were caused by change in ionization equilibrium or differences in the physical properties of calibration standards and analyzed samples, may be applied to ICP-OES. In some cases, a simple dilution for minimizing matrix effects can be performed [12]. Separation of matrix from the analyte elements is considered the most effective approach [13–15]. The matrix removal procedures reported in the literatures include solid phase extraction [16,17], chromatographic separation [18–20], and electrodeposition [21]. An alternative on-channel flow field-flow fractionation (FlFFF) for simultaneous matrix removal and analyte preconcentration procedure was also proposed by Al-Ammar et al. [22]. In their study, the matrix elements were removed by filtering off through the FlFFF membrane. The analyte elements were retained in the FlFFF channel by chelating with polymeric complexing agent, i.e., poly (ethylene imine) or PEI [23] for further elution and detection. Further developments on FlFFF matrix removal procedure were also reported recently [24,25]. According to Sangsawong et al. [24], FlFFF with cross flow matrix removal (CFM), or FlFFF/CFM, is an alternative way as a one step procedure for handling samples containing high salt Spectrochimica Acta Part B 66 (2011) 476–482 ⁎ Corresponding author. Tel.: +66 2 201 5129; fax: +66 2 354 7151. E-mail address: scasp@mahidol.ac.th (A. Siripinyanond). 0584-8547/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.sab.2011.04.012 Contents lists available at ScienceDirect Spectrochimica Acta Part B journal homepage: www.elsevier.com/locate/sab