Abstract

A low-pressure inductively coupled plasma atomic emission system with a double membrane desolvator (DMD) was built in the laboratory. For high solvent removal efficiency by the DMD, the plasma was easily turned on and sustained for more than 8 h while an aqueous sample solution was nebulized. The dimensions of the torch are similar to that of a mini-torch, but there is no intermediate tube. Inner diameters of the torch and the sample injector tube are 10 mm and 1.5 mm, respectively. The plasma gas flowed tangentially and formed a plasma. A narrow central channel was formed inside the plasma when the aerosol gas flowed, and atomic emission was observed at the end-on side of the plasma. The system was optimized by changing various operating factors while the Mg signal was monitored. As the flow rate of the plasma gas changed from 0.2 to 1.0 L min⁻¹, the signal-to-background ratio (S/B) increased. When the total gas flow of the DMD changed from 1.4 to 3.5 L min⁻¹ and the flow rate ratio of the inner to the outer gas was fixed at 5∶2, the S/B of Mg II doubled while the OH emission intensity decreased by approximately 67%. The chamber pressure was maintained in the range of a few Torr, which also influenced system optimization. Unlike atmospheric pressure ICP-AES, this low-pressure ICP system showed a much stronger intensity of the Mg II, 280.270 nm line compared to that of Mg I, 285.213 nm.