High resolution ICPMS as an on-line detector for flow field-flow fractionation; multi-element determination of colloidal size distributions in a natural water sample

Results are described from the first application of high resolution ICPMS coupled to flow field-flow fractionation (FlFFF-HR ICPMS), for the elemental characterization of small colloidal material (1-50 nm hydrodynamic diameter) in a natural freshwater sample. Detection limits for a 45 mL preconcentrated sample were 200 ng L−1 to 5 μg L−1 for major elements, 1-30 ng L−1 for most of the first row transition elements and <1 ng L−1 for rare earth elements. R.S.D. of the concentrations determined in five replicate measurements were less than 10% for 42 of the elements quantified. In total, 45 elements could be quantified, 15 more than were quantified in an earlier study performed with a quadrupole ICPMS. Direct on-channel preconcentration was used and the degree of preconcentration necessary was examined. The linearity between sample volume and calculated colloidal concentrations was good, but possible indications of sample losses were observed. Peak deconvolution analysis was carried out on some elements in order to obtain an estimate of the distribution of elements between organic carbon- and iron-rich colloids. Among the elements not previously studied, P, V and Ti were shown to associate strongly to iron-rich colloids, Br and I were exclusively bound to organic carbon colloids while As and Cd were equally distributed between the two. Sc corresponded to the pattern of lanthanides and Cr to the pattern of the other first row transition elements.