Modified high performance concentric nebulizer for inductively coupled plasma optical emission spectrometry

Abstract

The high performance triple-tube concentric nebulizer (HPCN) was modified and evaluated for sample introduction into inductively coupled plasma optical emission spectrometry (ICP-OES) at liquid flow rates of 0.25 to 0.8 mL min⁻¹. The acceptable liquid flow rate for the use of HPCN was extended by replacing the tapered center capillary tube of the nebulizer (i.d./o.d.: 50 μm/150 μm) with a large bore tube (i.d./o.d.: 110 μm/170 μm). The nebulization efficiency was much improved by reducing the inner diameter of the nebulizer nozzle from 250 μm to 200 μm. At a liquid flow rate of 0.8 mL min⁻¹ and a nebulizer gas flow rate of 1 L min⁻¹, the Sauter mean diameter (D_3,2) of the primary aerosol generated by the modified HPCN was 3.4 μm, and over 90% (v/v) of the aerosol droplets were below 10 μm in diameter. The D_3,2 value was smaller than those generated by conventional nebulizers, Meinhard nebulizer type C (8.2 μm), Glass Expansion Conikal nebulizer (15.8 μm), SeaSpray (14.8 μm), and MiraMist (5.6 μm). The amount of the tertiary aerosol of the modified HPCN generated through a non-baffled cyclone chamber was approximately 1.8 to 3.1 times higher than those of the other nebulizers, with similar size distributions. The sensitivity in ICP-OES with the modified HPCN was 1.5- to 3.2-fold higher than those with the other nebulizers when the liquid flow rates were the same. The plasma robustness estimated from the commonly used ratio Mg(II)/Mg(I) was the same or slightly better than that of the conventional nebulizers. The HPCN also showed a good tolerance to high total dissolved solids (TDS) using 20% NaCl solution. Validation of the modified HPCN was performed by a recovery test of spiked seawater and analyzing the NMIJ CRM 7502-a white rice flour. The observed values for the ten elements Na, Mg, P, K, Ca, Mn, Fe, Cu, Zn and Cd were in good agreement with their certified values. We concluded the modified HPCN is a very useful nebulizer for ICP-OES with good performance at a large range of sample flow rates.