µ-dDIHEN: a new micro-flow liquid sample introduction system for direct injection nebulization in ICP-MS

The µ-dDIHEN allows direct nebulization of small samples into the plasma at flow rate down to 5 µL/min. It is composed of a demountable direct injection high efficiency nebulizer (d-DIHEN), a flow injection analysis (FIA) valve and a gas displacement pump (GDP) connected to a µ-mass-flow meter delivering very stable liquid flow. The system was successfully tested with sample loops of 10 and 50 µL and for liquid flow rates between 5 and 50 µL/min on two different inductively coupled plasma mass spectrometry (ICP-MS) instruments, an HR-ICP-MS and an MC-ICP-MS, and for three different applications: boron isotopic ratio measurement of geological samples, multi-element analyses of natural water samples and gold nanoparticules characterization by single particle ICPMS (spICPMS). Signal sensitivity was increasing with liquid uptake rate of the µ-dDIHEN (and GDP gas flow rate), but not anymore above 30 µL/min, due to bad spray quality and poor ionization in extra-wet conditions. We successfully measured boron isotopic ratios (δ11B) for reference material solutions with B concentrations between 10 and 200 ppb, the reproducibility of the measurements depending on both the B concentration of the sample and the uptake rate: 10B signals below 20-30 mV (with 1011 ohms amplifiers) gave 2SD reproducibility ≥ 0.5 ‰ (n=5). Best measurement conditions were not necessarily with the lowest uptake rate but rather at 25 µL/min, allowing for higher signals. We also tested transient versus continuous measurement modes for a series of natural samples (with 10 and 50 µL sample loops). The two modes gave fully comparable results but the transient mode allows triplicated δ11B measurements and is recommended for very small samples (≤100 µL and B content of a few ng). For multi-element analyses by HR-ICP-MS, the limits of quantification (LOQ) of the majority of the trace and ultra-trace elements were lower (up to 15 times) with the µ-dDIHEN than with a concentric nebulizer and spray chamber, due to the much lower sample volume needed. Lastly, the µ-dDIHEN is highly promising for nanoparticles (NP) characterization by spICPMS. The first measurements for gold NPs of 40 nm certified size led to a transport efficiency of 85%.