A novel concentric grid nebulizer for inductively coupled plasma optical emission spectrometry

Abstract

A novel concentric type grid nebulizer (CGrid) was developed for sample introduction into an inductively coupled plasma optical emission spectrometer (ICP-OES). The CGrid has a concentric structure and a grid screen (over 350 meshes per inch) that is set inside the nozzle. The grid screen acts as both an effective gas–liquid mixing filter and a gas flow damper, and then the liquid breaks up into small droplets by passing through the grid with low velocity. By this unique nebulizing process, the CGrid showed excellent nebulizer performances on comparing with commercially available nebulizers, such as Meinhard nebulizer type C (MHN), modified high performance concentric nebulizer (m-HPCN), and OneNeb. The primary aerosols generated with the CGrid were finer and their velocities were lower than those with the other nebulizers. This nebulization feature gave a high transport efficiency of aerosols into the plasma, resulting in high sensitivity in ICP-OES. In the range of the liquid flow rate of 0.25 mL min⁻¹ to 2.0 mL min⁻¹ with the optimized nebulizer gas flow rate for obtaining the highest Mg(II)/Mg(I) signal intensity ratio, the maximum loading amount of aerosols into the plasma obtained with the CGrid was higher than those with the MHN (2.1-fold) and m-HPCN (1.4-fold), and almost the same as that with the OneNeb. The maximum sensitivity in ICP-OES obtained with the CGrid was 1.8- to 3.7-fold, 1.5- to 1.9-fold, and 1.1- to 1.2-fold higher than those with the MHN, m-HPCN, and OneNeb, respectively. The CGrid also showed a good tolerance for high total dissolved solid (TDS) concentrations. No clogging was observed when saturated NaCl solution was continuously nebulized for 5 hours. The limits of detection (LODs) obtained with the CGrid were better than those of the MHN, 1.6- to 5.3-fold improved, except for Cd I 228.802 nm, and similar to those of the m-HPCN and OneNeb. The plasma robustness estimated from the Mg(II)/Mg(I) signal intensity ratio obtained with the CGrid (10.6) was also better than those of the MHN (9.6), and similar to those of the m-HPCN (10.2) and OneNeb (10.4). The short-term stability on measuring spiked seawater (45 min) was within 3% of the relative standard deviation, and the recoveries of the spiked elements were in the range of 99% to 106%. The validation of the CGrid was performed by analyzing the NMIJ CRM 7531-a brown rice flour. The observed values for the five elements Mn, Fe, Cu, Zn, and Cd were in good agreement with their certified values. It was concluded that the CGrid is very useful for ICP-OES with good performance on sensitivity and high TDS solution analysis.