Desolvating the sample aerosol with microwave radiation: further theoretical and experimental insight into the significance of such approach

This study aims to determine the feasibility of using microwave energy to achieve significant improvements in sample introduction by desolvating a sample aerosol. The efficiency and mechanism of microwave desolvation were investigated. Evidence for significant interaction between aqueous droplets and microwave energy was evaluated by experimental and theoretical methods. A microwave desolvation system incorporating a Nafion dryer was evaluated for ICP-MS. A small improvement in transport to the plasma (between 51 and 60%) was observed for magnesium, lead, and rhodium with 100% microwave power. The mechanism of desolvation was investigated using a different microwave system connected to a flame spectrometer. This system was heated, and sample introduced in the presence of a microwave field and in the absence of microwaves. No significant difference between the two cases was found indicating that the primary mechanism for increased sample transport was conductive heating of the droplets. A numerical model was developed and showed that small droplets (5 μm) are incapable of absorbing sufficient energy from a 2.45 GHz field to heat significantly due to very small absorption efficiencies as predicted by Mie theory calculations.