High performance concentric nebulizer for low-flow rate liquid sample introduction to ICP-MS

A high performance concentric nebulizer (HPCN) was developed for sample introduction to inductively coupled plasma mass spectrometer (ICP-MS) at liquid flow rates of less than 10 mu L min(-1). The HPCN has a triple tube concentric structure and consists of a concentric type nebulizer body and a fused silica glass capillary (i.d./o.d.: 50 mu m/150 mu m) mounted in the center of the nebulizer body as a sample introduction capillary. The nebulizing performance was greatly improved by tapering the liquid capillary (tip orifice i.d.: 20 mu m, tip wall thickness: <8 mu m) and by setting the liquid capillary tip at a proper position. When the set position was recessed by 25 mu m to 50 mu m with respect to the nebulizer nozzle tip, a liquid jet was produced inside the nozzle by a flow focusing effect. This phenomenon gives a fine aerosol generation. At a liquid flow rate of 5 mu L min(-1) and a nebulizer gas flow rate of 1 L min(-1), the Sauter mean diameter D-3,D-2 of the primary drops generated by the HPCN (2.4 mu m) was almost the same as that generated by the HEN-120-A.01 (2.6 mu m) and was smaller than those generated by the HEN-90-A.01 (4.6 mu m), CEI-100 (5.9 mu m), and AriMist-HP (6.3 mu m). The sensitivity in ICP-MS with the HPCN was over two-fold higher than those with the other microflow nebulizers, except for the HEN-120-A.01. The HEN-120-A.01 provides almost the same sensitivity as the HPCN, but it requires two-fold higher gas pressure than the HPCN. The HPCN can continuously and stably nebulize 1% NaCl solution for over 8 h without clogging. The HPCN combined with an on-axis cylinder chamber was applied to capillary liquid chromatography-ICP-MS, by which the speciation of eight arsenic compounds was demonstrated. We concluded the HPCN is a useful nebulizer for less than 10 mu L min(-1) sample introduction to ICP-MS.