Towards nanoparticle analysis using N₂ MICAP-MS: Employed gases, carbon enhancement, and alcohol tolerance

To evaluate the capabilities of the nitrogen-sustained MICAP-MS for nanoparticle analysis with a dual sample introduction setup, the droplet detection efficiencies were determined when employing He, N₂, or a mixture thereof. Introducing droplets in a pure nitrogen environment was possible, but it lowered the droplet transport and increased temporal jitter. Analysis of gold nanoparticles was carried out using the droplet calibration approach for nanoparticle size and number concentration, yielding a good agreement with the reference values. Investigating a possible increase in the gold sensitivity via the carbon enhancement effect, solutions containing up to 94 % v/v methanol were analysed using nitrogen, argon, and air as nebulizer gases. As opposed to Ar ICP-MS, no substantial signal enhancement could be achieved with N₂ or Ar for As, Se, and Au, even with the highest concentration. A notable increase was obtained only for Au when using air, but the fundamentally lower sensitivity limits its analytical usefulness. Furthermore, the N₂ MICAP-MS could be operated stably with alcohol contents up to 96 % v/v EtOH and 75 % v/v 2-PrOH. Analyte sensitivities for high IE elements in these solvents were maximized at 75 % v/v MeOH and 25 %v/v 2-PrOH, while 75 % v/v EtOH yielded improvement for all investigated elements except Au. Limits of detection in the three alcohols were highly dependent on IE and m/z, and sub ng kg^-1 values for Y and Cs, while LODs of 10s of ng kg^-1 were obtained for As, Se, and Au in MeOH.