Abstract
Asymmetrical flow field-flow fractionation (AF4) is a powerful technique employed for the separation of macromolecules, nanoparticles, and their assemblages according to their hydrodynamic behavior. It is well known that at this size range, complex interactions can occur between components (e.g. surface adsorption, aggregation) controlling the fate of trace metals (TMs) bound to them. AF4 coupling to inductively coupled plasma mass spectrometry (ICP-MS) allows the quantification of metal-containing species at trace levels present in environmental and biological systems on a size-composition basis. The combination of AF4-ICP-MS with other online detectors provides additional information that allows the assessment of the origin of analytes present in mixtures and complex matrixes with minimal sample preparation, which is crucial for understanding the behavior of trace metal contaminants. Despite the increasing use of AF4-ICP-MS in environmental contexts, we acknowledge that the quantification of inorganic species using such combined techniques requires further development of standardized procedures and need certified reference materials. In this review, we also discuss critical endpoints within the ICP-MS instrument coupled to AF4 that need to be controlled before quantitative measurements can be validated. Then, we illustrate how the combination of different online detectors in addition to ICP-MS offers an integrated picture of natural components states, thus providing key information on the changes in behavior of trace metal species and metallic nanoparticles (MNPs) as observed in both environmental samples and biofluids.
Highlights
Determining the physicochemical speciation of trace metals (TMs) is a central topic in inorganic biogeochemistry, as various chemical and physical forms exhibit different fate, bioavailability, and impact on aquatic environments
We tested three independent ways of quantifying the metal content for the peptide metallothionein (MT1) from fractograms obtained with the AF4 outflow coupled directly to the nebulizer (Fig. 2): using continuous introduction of ionic multi-element standards and non-transient time acquisition of the signals with dilution made in either (i) 2% HNO3, or in (ii) 10 mM HEPES pH = 7.0 (2-[4-(2-hydroxyethyl) piperazin-1-yl]ethanesulfonic acid, organic eluent for MT1 optimized fractionation) but supplemented with a chelator (2,2',2'',2'''-(ethane-1,2-diyldinitrilo) tetra-acetic acid, EDTA) to stabilize cations in solution, and (iii) flow injection analysis (FIA) of EDTA-stabilized standards where the outflow of the AF4 was coupled directly to the nebulizer inductively coupled plasma mass spectrometry (ICP-MS)
In this review, we critically discussed the current state-ofthe-art concerning AF4-ICP-MS coupling with an emphasis on the existing challenges and possible solutions when this versatile technique is used for quantification and size-characterization of metal-containing species in complex samples from environmental and biological origin
Summary
Determining the physicochemical speciation of trace metals (TMs) is a central topic in inorganic biogeochemistry, as various chemical and physical forms exhibit different fate, bioavailability, and impact on aquatic environments. AF4 provides some advantages as compared to other size separation techniques, for the online ICP-MS analysis of low concentrations of analytes: (i) minimal exposure of the analytes to surfaces that lessens their loss, (ii) possibility to separate analytes in mobile phases appropriate for ICP-MS,[20] (iii) minimizing sample handling decreasing the risk of metal contaminations of the samples, and (iv) allows the introduction of large volumes in the channel (up to 100 mL) given the initial focusing step during sample injection,[21] improving the detection limit of trace components.[22]. We will provide different illustrations of the multidimensional information obtained with the use of series of online detectors that allows simultaneous quantification of these species according to their size and their nature Such information is central for understanding their physicochemical speciation and their reactivity and impacts in aquatic environments and biofluids. Low concentration of natural nano-sized species can make their detection a challenge
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