Capillary electrophoresis/inductively-coupled plasma-mass spectrometry: development and optimization of a high resolution analytical tool for the size-based characterization of nanomaterials in dietary supplements.

We report the development and optimization of a system consisting of capillary electrophoresis (CE) interfaced with inductively coupled plasma mass spectrometry (ICPMS) for rapid and high resolution speciation and characterization of metallic (e.g., gold, platinum, and palladium) nanoparticles in a dietary supplement. Multiple factors, including surfactant type and concentration, pH of running buffer, and applied voltage, were investigated to optimize the separation conditions. It was found that by using the anionic surfactant sodium dodecyl benzenesulfonate (SDBS) in the running buffer the separation resolution was significantly improved, allowing for easy distinction of adjacent size fractions in a gold nanoparticle mixture with very small size differences (e.g., 5, 15, 20, and 30 nm). The type and concentration of the surfactant was found to be critical in obtaining sufficient separation while applied voltage and pH values of the running buffers largely affected the elution times by varying the electroosmotic flow. Quantum dots were used as mobility markers to eliminate the run-to-run variation. The diameters of the nanoparticles followed a linear relationship with their relative electrophoretic mobility, and size information on unknown samples could be extrapolated from a standard curve. The accuracy and precision of this method was confirmed using 10 and 30 nm gold nanoparticle standard reference materials. Furthermore, the method was successfully applied to the analysis of commercially available metallic nanoparticle-based dietary supplements, as evidenced by good agreement between the particle sizes calculated by CE/ICPMS and transmission electron microscopy (TEM).