Journal of Chromatography A, 1206 (2008) 160–165 Contents lists available at ScienceDirect Journal of Chromatography A j o u r n a l h o m e p a g e : w w w . e l s e v i e r . c o m / l o c a t e / c h r o m a Optimisation of asymmetrical flow field flow fractionation for environmental nanoparticles separation S. Dubascoux a,∗ , F. Von Der Kammer b , I. Le Hécho a , M. Potin Gautier a , G. Lespes a a LCABIE CNRS UMR 5254 IPREM, Helioparc, av du Président Pierre Angot, 64053 PAU, France b Center of Earth Sciences, Nanogeosciences, Vienna University Althanstrasse 14, A-1090 Vienna, Austria a r t i c l e i n f o Article history: Received 10 June 2008 Accepted 14 July 2008 Available online 18 July 2008 Keywords: Asymmetrical Flow Field Flow Fractionation Optimisation Environmental nanoparticles a b s t r a c t The fractionation of natural nanoparticles by Asymmetrical Flow Field Flow Fractionation (As-Fl-FFF) was optimised by considering the following operating conditions: ionic strength, surfactant concentration and crossflow rate. The method performances such as fractionation recovery and fractionation efficiency were evaluated on a stable solution of colloidal-size natural inorganic particles. The online multi-detection by ultraviolet/visible spectrophotometer (UV) and multi-angle laser light scattering (MALLS) provided the monitoring of the sample during the separation and the evaluation of the fractionation efficiency. The lowest ionic strength and surfactant concentrations (i.e. 10 −3 mol L −1 NH4NO3 and 3 × 10 −4 mol L −1 SDS) allowed to obtain the highest sample recovery and lowest loss of the largest particles. The crossflow rate was investigated in order to avoid significant membrane–sample interaction. The applicability of the fractionation in optimised conditions was evaluated on a natural soil leachate, which was filtrated with different filter cut-offs. Filtration efficiency was stressed by the decrease of the large unfractionated particle influence in the void volume.For the first time,robust operating conditions were proposed to well size-fractionate and characterize soil nanoparticles within a single multi-detection analysis. © 2008 Elsevier B.V. All rights reserved. 1. Introduction Environmental colloids are of high interest because of their role especially in pollutant and trace element mobility, bioavailabil- ity and transfer [1,2]. The IUPAC definition of colloids refers to compounds (organic or inorganic) with size ranged from 1 nm to 1 ␮m in one dimension. Natural colloids are extremely diversified in the environment due to the definition by the spatial dimen- sion, covering a large variety of different entities in environmental media such as clays, iron oxyhydroxide, humic compounds, micro- organisms,their associations,aggregates and many others [3]. In groundwater,they could be divided into two main parts: organic matter compounds (small organic colloids with sizes in the lower nanometre range) and inorganic particles (ranging from some nm to hundreds nm) [4]. This second part is often called nanoparticles. Different techniques exist to separate colloids and particles: sieving and (ultra-)filtration, sedimentation and centrifugation, Field Flow Fractionation (FFF),size exclusion chromatography and capillary electrophoresis [5,6]. Even if sieving/filtration and sedimenta- tion/centrifugation remain the most used fractionation techniques for environmental colloids, FFF is the most capable and versa- ∗ Corresponding author. Tel.: +33 559407762. E-mail address: gaetane.lespes@univ-pau.fr (S. Dubascoux). tile technique for colloid separation in terms of separation range, selectivity and resolution [1,6].FFF theory is now well described [7]. The technique is used in several fields: polymer technology, biotechnology, pharmaceutics, biopharmaceutics and environmen- tal chemistry [8–11]. The coupling to a series of specific detectors enables a detailed characterization of colloid properties as a func- tion of their sizes. Briefly the FFF colloidal separation principle takes place under the effect of a field applied perpendicularly to a main parabolic flow of mobile phase. The main difference between FFF and chro- matography is that the separation is not based on interaction between analytes and a stationary phase but on the interaction of the analytes with the field in a non-uniform flow [7]. Sub- techniques of FFF are distinguished according to the nature of the field applied. Flow Field Flow Fractionation (Fl-FFF) is one of these sub-techniques where the field is created by a secondary flow of mobile phase perpendicular to the main one (cross- flow). In Asymmetrical Flow Field Flow Fractionation (As-Fl-FFF) the crossflow is applied in a semi-permeable channel covered by a membrane characterized by variable cut-off and nature. The main difference between symmetrical and asymmetrical channel is that in As-Fl-FFF the crossflow is created by a difference in carrier in- and outflow volumetric flow rate instead of a secondary pump directing the crossflow via a top-channel frit into the channel. This 0021-9673/$ – see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.chroma.2008.07.032