New Orientation: A Downward-pointing Vertical Inductively Coupled Plasma Mass Spectrometer for the Analysis of Microsamples.

We present a prototype of a vertical-downward configuration of an inductively coupled plasma mass spectrometer (ICPMS) allowing the sample introduction from the top. With this novel approach to orient the ICP downward, we aim to expand the sample transport capabilities in ICPMS especially for the transport of droplets or particles with a final goal to analyze individual cells. Because of this gravity-assisted sampling approach, the transport of larger sized droplets, that is, droplets that would be difficult to transport into a horizontally oriented ICPMS, becomes possible and, furthermore, becomes independent of the droplets' size or size distribution. We demonstrate that droplets of an initial size of 70 μm can be successfully transported into the plasma at dispensing frequencies up to 1 kHz without the need for a desolvation device. In addition, we observed that the implementation of a desolvation device, that is, a gas-exchange device (GED), can improve the detection efficiencies (DEs). Compared to operating conditions that are commonly reported for ICPMS experiments, significantly different optimization parameters (radio frequency power and gas flow rates) were tested in the presented experiments here while instrument type-specific DEs were obtained.