Analysis of gold nanoparticle mixtures: A comparison of hydrodynamic chromatography (HDC) and asymmetrical flow field-flow fractionation (AF4) coupled to ICP-MS

Robust methods to detect and characterize engineered nanoparticles (ENPs) in environmental samples are an urgent need, particularly given the increasing use of ENPs in consumer products. To be successful, methods should enable differentiation of ENPs from background nanoparticulates and other system components. The element specificity of inductively coupled plasma mass spectrometry (ICP-MS) can, to some degree, satisfy this requirement. Given the polydisperse nature of particles in natural systems, combining ICP-MS with a size separation method holds particular promise. This paper compares hydrodynamic chromatography (HDC) and asymmetrical flow field flow fractionation (AF4), both coupled with ICP-MS, in their capacity to detect, quantify, and characterize nanoparticles. The detection limits, resolution, and recoveries for both techniques were determined using gold nanoparticle standards. AF4 is capable of separating mixtures of 5, 20, 50 and 100 nm gold ENPs with significantly greater resolution than HDC, with these resolution differences being most pronounced in the smaller size range. However, HDC recoveries ranged from 77 to 96%, while recovery during AF4 ranged from 4 to 89%. The low AF4 recoveries generally occurred for the largest ENPs at the lowest concentrations examined. The limits of detection for both techniques were found to be approximately 5 μg L ^-1, however different experimental conditions could lower this value. HDC provides an additional benefit over AF4 by proving capable of separating a dissolved signal from a NP sample.