Characteristics of a High-Power Microwave-Induced Helium Plasma at Atmospheric Pressure for the Determination of Nonmetals in Aqueous Solution

Abstract

A high-power [∼ 1000 W continuous wave (CW), 2.45 GHz] annular-shaped microwave-induced helium plasma (He-MIP) was developed for the determination of nonmetals in aqueous solutions, and the characteristics are presented. The plasma was generated at atmospheric pressure by an Okamoto cavity that was modified to focus the energy. No external cooling was used to stabilize 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 10¹⁴/cm³ and 5000 K, respectively. Introduction of aqueous chloride in the form of NaCl and bromide in the form of KBr produced intense ion emission, and detection limits of 100 ppb for Cl(II) (479.5 nm) and 200 ppb for Br(II) (470.5 nm) were obtained.