Hyphenation of field-flow fractionation and single particle ICP-MS for the assessment of number-based particle size distributions at ultratrace levels

R. Reed, T. Pfaffe, S. Tadjiki, E. Moldenhauer, F. Meier, T. Klein
Postnova Analytics Inc.,
United States

Keywords: nano, field flow fractionation, single particle ICP-MS, characterization, number concentration, particle size

Summary:

One of the challenges in characterization of complex nanomaterials in the environment is to obtain number based information such as particle concentration and size distribution at environmentally relevant concentrations, typically predicted to be in the ng/L or µg/L range in surface waters. The combination of field-flow fractionation and inductively coupled plasma mass spectrometry (FFF-ICP-MS) has been proven to be a powerful analytical technique for characterization of environmental samples [1-3], but it lacks a direct measurement of particle number concentration since the ICP-MS is used in the traditional “bulk” analysis mode. Single particle ICP-MS (spICP-MS) is a relatively new and rapidly advancing analytical technique which can provide number based information for monodisperse metal and metal oxide nanoparticles at ng/L concentrations [4, 5]. This presentation reports direct hyphenation of spICP-MS to both asymmetrical flow FFF and centrifugal FFF systems. The spICP-MS was utilized as an online particle number detector for characterization of gold, silver, silica and titania nanoparticles as well as different mixtures thereof. The hyphenated technique was able to measure the number-based concentrations and size distributions of the nanoparticles by counting and sizing the respective nanoparticle mixtures in one single run. In general, the ability of spICP-MS to discriminate particle pulses from background is diminished when there is a large amount of dissolved analyte present. Dissolved Ag (µg/L levels) was added to a mixture of Ag nanoparticles (ng/L levels) prior to separation by asymmetrical flow FFF. The semi-permeable membrane (10 kDa cut-off) in the FFF channel allowed the removal of dissolved Ag during the focusing step, thereby improving the ability of the coupled spICP-MS detector to discriminate particles from background. References 1. Taylor, H.E., et al., Inductively coupled plasma-mass spectrometry as an element-specific detector for field-flow fractionation particle separation. Analytical Chemistry, 1992. 64(18): p. 2036-2041. 2. Lesher, E., et al., Field-Flow Fractionation Coupled to Inductively Coupled Plasma-Mass Spectrometry (FFF-ICP-MS): Methodology and Application to Environmental Nanoparticle Research, in Field-Flow Fractionation in Biopolymer Analysis, S.K.R. Williams and K.D. Caldwell, Editors. 2012, Springer Vienna. p. 277-299. 3. v. d. Kammer, F., et al., Colloidal Particles in Sediment Pore Waters: Particle Size Distributions and Associated Element Size Distribution in Anoxic and Re-oxidized Samples, Obtained by FFF-ICP-MS Coupling. Acta hydrochimica et hydrobiologica, 2003. 31(4-5): p. 400-410. 4. Pace, H.E., et al., Single Particle Inductively Coupled Plasma-Mass Spectrometry: A Performance Evaluation and Method Comparison in the Determination of Nanoparticle Size. Environmental Science & Technology, 2012. 46(22): p. 12272-12280. 5. Mitrano, D.M., et al., Silver nanoparticle characterization using single particle ICP-MS (SP-ICP-MS) and asymmetrical flow field flow fractionation ICP-MS (AF4-ICP-MS). Journal of Analytical Atomic Spectrometry, 2012. 27(7): p. 1131-1142.