Development of Direct Injection Multi-gas ICP and Its Application of Elemental Analysis

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Inductively coupled plasma mass spectrometry(ICP-MS) and ICP atomic emission spectrometry (ICP-AES) using argon ICP as an ionization or an excitation source have been widely utilized for trace elemental analysis. Unfortunately, it was difficult to excite high ionization potential elements because the ionization ability of argon plasma is not enough high. To overcome this problem, development of other powerful plasma sources, for example helium ICP, are expected.In our research group, a new direct injection multi-gas ICP source for MS and AES has been developed. With the new ICP source, not only Ar but He, O_2, N_2, CO_2, N_2O, air and their mixture plasmas can be stably generated in atmospheric pressure. The torch consists of coaxial three quartz glass tube structure and the cooling gas, the plasma gas and the carrier gas flow between the tubes. To generate an adequate vortex flow at the plasma generating region even when helium gas is used, the torch has smaller gas inlet and short to … More rch configuration. Helium has about nine times higher kinematic viscosity than other gases so the vortex flow of helium easily turn into the laminar flow. It is apprehended that the cooling gas may immix into the plasma and it cause increasing of background emission for AES and background ion for MS. In this study, effect of the cooling gas kind and the flow rate on the emission properties in Ar and He ICP are investigated. The radial emission intensities of N_2, Ar and He are measured. As a result, it was found that when appropriate gas and flow rate are chosen, mixture of not only cooling gas but atmosphere into the plasma are reduced.Furthermore, aqueous solutions can be directly introduced into the plasma like DIN (direct injection nebulize) or DIHEN (direct injection high-efficiency nebulizer) using conventional nebulizers. The new torch has a support gas flow around the nebulized solutions to reduce diffusion of the solutions into the plasma. As a result, the diffusion angle of the injected solutions effectively reduced. Then the emission intensities from the sample are increased and the experimental conditions for stable generation of plasmas with direct injection are expanded. The spectroscopic characteristics of the new direct injection multi-as ICP source are investigated. Less