Gaëtane Lespes

Field-flow fractionation and inductively coupled plasma mass spectrometer coupling: History, development and applications

Field-Flow Fractionation (FFF) is now recognised as a versatile pool of techniques allowing particle size or molar mass to be obtained in a wide variety of samples covering numerous applications in the fields of environment, materials or biology. In the same time, Inductively Coupled Plasma-Mass Spectrometry (ICP-MS) has an indisputable place in the field of elemental detectors and the coupling between FFF and ICP-MS can be considered as an emerging technique capable to reach relevant physico-chemical information at sub-micrometre scale and trace element concentration level. This paper gives some key elements of FFF-based fractionation linking theory and practical analytical aspects, from injection and preconcentration to analysis. The different components of the coupling are described. Summary tables of the main operating conditions of FFF-ICP-MS coupling are presented and operating conditions such as carrier composition, flow and nebulizers are discussed. Special attention is given to the FFF-ICP-MS interface. Qualitative and quantitative analysis is also discussed. Applications in the fields of environment, bioanalysis and nanoparticles are presented in order to illustrate the potentialities of such coupling.

Improved routine speciation of organotin compounds in environmental samples by pulsed flame photometric detection

The high toxicity of the organotin species requires sensitive analytical methods in order to understand the origins of pollution and perform monitoring programs in the water cycle. The optimisation of a new detection method, pulsed flame photometric detection (PFPD), is reported for the simultaneous determination of butyl-, phenyl- and octyltins. The methodology of the experimental designs at two levels was used. It allows the evaluation of the influence of the three gas flow-rates on the peak heights and resolution between the closest peaks obtained using two different wavelengths of detection (390 and 611 nm). The modelling of these two responses, according to second-order polynomials, leads to the precise adjustment of the operating conditions. PFPD has shown two significant improvements over conventional flame photometric detection: increased sensitivity (absolute detection limits: 0.07 to 2 pg as Sn) and greater selectivity, whatever the wavelength used. This new analytical process was validated by the analysis of certified reference material and spiked river water. It was used in routine analysis of environmental samples (wastewater, sludge, sand and oyster).

Optimisation of asymmetrical flow field flow fractionation for environmental nanoparticles separation

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 x 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.

Rapid determination of organotin compounds by headspace solid-phase microextraction.

Headspace solid-phase microextraction (SPME) followed by gas chromatography (GC) coupled to pulsed flame photometric detection have been investigated for the simultaneous speciation analysis of 14 organotin compounds, including methyl-, butyl-, phenyl-, and octyltins compounds. The analytical process (sorption on SPME fibre and thermal desorption in GC injection port) has been optimised using experimental designs. Six operating factors were considered in order to evaluate their influence on the performances of a SPME-based procedure. The evaluation of accuracy, precision and limits of detection (LODs) according to ISO standards and IUPAC recommendations has allowed the method to be validated. The LODs obtained for the 14 studied organotins compounds are widely sub-ng(Sn) l(-1). The precision evaluated using relative standard deviation ranges between 9 and 25% from five determinations of the analytes at 0.25-125 ng(Sn) l(-1) concentrations. The accuracy was studied throughout the analysis of spiked environmental samples. These first results show that headspace SPME appears really as attractive for organotins determination in the environment and the monitoring of their biogeochemical cycle.

Optimization of solid-phase microextraction for the speciation of butyl- and phenyltins using experimental designs

Abstract This paper deals with the optimization of solid-phase microextraction (SPME) for organotin speciation in water. The analytical method consists of an in situ ethylation, simultaneous solid-phase microextraction of the derivatives, followed by a gas chromatographic analysis with flame photometric detection. Experimental design methodology was used to evaluate the influence of six analytical parameters on the mean peak area (Smean). The adsorption of the compounds on the SPME fibre was found to be the most important parameter and two other factors are positively significant: the adsorption time and the sample volume. The adsorption profiles and the optimal operating conditions were determined from the modelling of Smean. The detection limits range from 2 to 4 ng l−1 (monophenyltin excepted: 18 ng l−1) and linearity is from 50 to 600 ng l−1. The relative standard deviations are 7–10% for five determinations. Water samples were analysed in order to verify the accuracy of the optimized method by comparing results with those obtained using a conventional solvent extraction of the ethylated organotins.

Solid phase microextraction (SPME) : a new procedure for the control of butyl- and phenyltin pollution in the environment by GC-FPD

A new alternative to liquid–liquid extraction for the speciation of organotin compounds is proposed using NaBEt4 ethylation–simultaneous solid phase microextraction (SPME)–GC-FPD. SPME is carried out using a polydimethylsiloxane (PDMS) fibre immersed in 100 ml of solution for an adsorption time of 60 min. The optimisation step confirms the importance of stirring the solution. The higher efficiency of mechanical stirring is also clearly demonstrated. Under these conditions, SPME was applied for the first time to the simultaneous extraction of butyl- and phenyltins and the analytical performances were evaluated. Very low detection limits were reached, in the range 0.006–0.031 ng Sn l−1 for butyltins and 0.2–0.6 ng Sn l−1 for phenyltins. The repeatability is also improved compared with classical liquid–liquid extraction thanks to the small volume of the fibre and the on-line procedure (between 3 and 9% except for triphenyltin). The new method was applied to various environmental samples such as natural aqueous samples, sediment and sewage sludge. The competitive extractions between some organotins and organic matter present in complex matrices are discussed.

Determination of Butyltin and Phenyltin by GC–FPD Following Ethylation by NaBEt4

An organotin speciation method was optimized for the simultaneous determination of mono-, di- and tri-butyltin compounds and mono-, di- and tri-phenyltin compounds in water. The procedure was based on a one-step simultaneous ethylation and extraction using the sodium tetraethylborate reagent directly in the aqueous phase in the presence of an isooctane layer. Direct extract analysis was performed using capillary gas chromatography and flame photometric detection (GC-FPD). This derivatization procedure reduces drastically the number of analytical steps, thus saving time and improving reliability. Relative detection limits range from 0.4 to 0.8 ng dm -3 for butyltin species and from 0.7 to 2.1 ngdm -3 for phenyltin species; the linearity ranges from 0 to 400 ngdm -3 . Analysis of environmental aqueous samples and a Certified Reference Material (CRM) demonstrates the accuracy of the analytical method.

Hyphenated analytical techniques for multidimensional characterisation of submicron particles: A review

The stakes concerning the characterisation of particles ranged in the size from 1 to 1000 nm, namely submicron particles, are today more and more important. Because of the variety of particles even inside a given sample in terms of dimension, mass, charge or chemical composition a characterisation as complete as possible is needed. The possibility of obtaining a multidimensional information by relevant analytical methods is then of the greatest interest. One very interesting strategy consists in using hyphenated techniques, which are intrinsically capable to provide rapidly and accurately such information. This paper summarises the different hyphenated techniques that can be used to characterise submicron particles and is focussed on their main applications to illustrate their current and potential uses. In order to have a relevant overview various on-line separation techniques are considered in a comparative way. In the same way various on-line detectors are then presented. Finally the concepts of multidetection and multidimensional analysis are discussed and their interest showed through different typical examples of hyphenated techniques illustrating submicron particle characterisation in fields of applications such as environmental and nanomaterial sciences.

Colloidal organic matter from wastewater treatment plant effluents: Characterization and role in metal distribution

Colloidal organic matter from wastewater treatment plants was characterized and examined with respect to its role in metal distribution by using tangential flow ultrafiltration, liquid chromatography coupled with organic carbon and UV detectors, and an asymmetrical flow field-flow fractionation (AFlFFF) multidetection platform. Results revealed that a humic-like fraction of low aromaticity with an average molar mass ranging from 1600 to 2600Da was the main colloidal component. High molar mass fractions (HMM), with molar mass ranges between 20 and 200kDa, were present in lower proportions. Ag, Cd, Cu, Cr, Mn and Zn were found mainly in the dissolved phase (<0.45microm) and their distribution between colloidal and truly dissolved fractions was strongly influenced by the distribution of dissolved organic carbon. AFlFFF coupled to ICP-MS showed that Ag, Cd, Cu, Cr, Mn and Zn associate to the low molar mass fraction of the colloidal pool, whereas Al, Fe and Pb were equally bound to low and high molar mass fractions.

Determination of butyl- and phenyltin compounds in sediments by GC-FPD after NaBEt4 ethylation

A reliable and rapid speciation method for the simultaneous determination of butyl- and phenyltin species in sediment samples has been developed. Two extraction procedures are compared: methanolic hydrochloric acid (at four different concentrations) and ethanoic acid leaching. Derivatization is carried out by the one-step ethylation/extraction procedure using the sodium tetraethylborate reagent directly in aqueous phase in the presence of an isooctane layer. Analysis is performed by capillary gas chromatography hyphenated to flame photometric detection (GC-FPD). Detection limits range from 0.5 to 1.5 ng(Sn) g(-1)(dry weight). Analysis of environmental samples and certified reference materials demonstrate the accuracy of the analytical method.