Production of High-Power Microwave-Induced Helium Plasma at Atmospheric Pressure for Trace Element Analysis

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A high-power (〜1 kW, 2.45 GHz) annular-shaped microwave-induced helium plasma at atmospheric pressure was developed for determination of nonmetals in the aqueous solutions. The plasma was generated by an Okamoto cavity (Y. Okamoto, Anal. Sci. 7 (1991) 283) which was modified to focus the energy and low gas flow rate )101/min). No external cooling was used to stabilized the plasma. An aqueous solution was injected into the plasma by an ultrasonic system with desolvation and condensation. The electron density and iron excitation temperature were on the order of 10^<14>cm3 and 5000 K, respectively. Introduction of aqueous fluoride in the form of NaF, chloride in the form of NaCl, and bromide in the form of KBr produced intense emission and detection limits of 100 ppb for FI(685.6 nm), 100 ppb for Cl II(479.5 nm), and 200 ppb for Br II(470.5 nm) were obtained.