Single particle and single cell analysis by ICP-MS with pneumatic nebulisation: Comparing sample introduction systems

Inductively coupled plasma-mass spectrometry (ICP-MS) operated in the single particle (sp) and singe cell (sc) modes belongs to the methods of elemental analysis that has significantly grown during the last years. Its contribution to the characterisation of nanomaterials and cell populations has opened new avenues and possibilities in many different disciplines. In this context, pneumatic nebulisation plays a pivotal role since it is still the preferable sample introduction system in ICP-MS. Reliable quantitative data are only accessible with known transport efficiency (TE) of the small objects, so that the determination of this parameter is extremely critical. In this study, we investigated various combinations of commercially available nebulizers and spray chambers for testing their performance in sp- and sc-ICP-MS. Two configurations made use of high sample flow rates of 0.4 mL/min with a "traditional" cyclonic spray chamber, and another four combinations employed spray chambers especially designed for total consumption used at optimum flow rates of 10 μL/min (Cytospray and HE-SIS). Achievable sensitivities were significantly better for the high consumption set-ups (about 5-fold). Transport efficiencies determined by the particle number method were evaluated by the use of three different model suspensions: i) 30 nm standard gold nanoparticles LGCQC5050, ii) europium-loaded polystyrene beads, and iii) selenized yeast SELM-1. Significant differences between the three suspensions were observed obtaining results up to 90 % for certain configurations. In fact, these differences imply that for different approaches (sp- or sc-ICP-MS) a suitable calibrant has to be used for the accurate determination of the transport efficiency.