A Critical Comparison of Ar and Ar-N₂ Inductively Coupled Plasmas as Excitation Sources for Atomic Emission Spectrometry

Abstract

Ar-N2 plasmas generated by introducing N2 into the outer and the aerosol carrier gas flows were investigated using a 5 kW, 27.12 MHz crystal-controlled rf generator. The dependence of plasma geometry, plasma background intensity, net analyte emission intensity, signal/background ratio, signal/noise ratios, and the detection limits on forward power (1000 to 4000 W), the outer gas flow (15 to 50 liters/min) and aerosol carrier gas flow (1 to 2.5 liters/min), sample uptake rate (1 to 5 ml/min), and gas composition (0 to 100% N2) were studied for observation heights of 5 to 40 mm. Measurements were conducted simultaneously for 20 ion and neutral atom spectral lines. Ultrasonic nebulization, with aerosol desolvation, was employed. Except for the observation height, which was 10 mm, the optimum conditions for Ar-N2 plasmas containing 5 to 15% N2 in the outer gas flow were roughly identical to those of a conventional Ar plasma. When pure N2 was used in the outer flow, two sets of optimum conditions, quite different than the optimum conditions for the conventional Ar plasma, were found for the high and medium excitation energy lines. Detection limits and signal/background ratios of ion and neutral atom lines of the high excitation energies, excited in a pure Ar plasma, were superior to the results obtained in the Ar-N2 plasma when pure N2 was used in the outer flow. The opposite trend was observed for neutral atom lines of medium excitation energies. The use of N2 aerosol carrier gas, when the outer gas flow was pure Ar, deteriorated the detection limits of all elements.

Improvement of Analytical Sensitivity by Ar-N2 Inductively Coupled Plasma in Axially Viewing Optical Emission Spectrometry

“…Similar phenomena were also reported for Ar-N2 ICP in radially viewing OES. [4][5][6] When the N2 gas was added into the Ar ICP, enhancements of the net signal intensity of elements were observed as shown in Figs. 1 and 2, though no optimization on the spectrometer with respect to the Ar-N2 ICP was performed.…”

“…The analytical sensitivities on these elements with relatively higher ionization energies obtained by axially viewing Ar-N2 ICP-OES in the present study were superior to those obtained by radially viewing Ar-N2 ICP-OES reported previously. [4][5][6]9,10 It is expected that the axially viewing Ar-N2 ICP-OES also show better analytical performance for elements with higher ionization energies, such as As, Br, Cl, I, Hg, P, S, Se.…”

“…The uptake rate of solutions introduced into the ICP was controlled at 1.0 mL min -1 by a peristaltic pump. Sciences,[1][2][3][4][5][6][7] Obuchi, Japan The analytical sensitivities of elements were improved by Ar-N2 inductively coupled plasma (Ar-N2 ICP) in axially viewing optical emission spectrometry (OES). A commercially available ICP-OES instrument was used, and only N2 gas was added at flow rates of up to 1.0 L min -1 into Ar plasma gas.…”

“…1,4 These ICPs sometimes showed better analytical performances compared with Ar ICP-OES; however, they have not been applied to commercial ICP-OES instruments because of some difficulties and complexities concerning the plasma operating conditions and optimization with respect to OES analysis. 1,[4][5][6] It should also be remarked that these reported ICPs were examined only in radially viewing ICP-OES. 1,[4][5][6] In the present study, we found an effective sensitivity enhancement of elements in axially viewing ICP-OES by adding N2 gas into the Ar plasma gas.…”

“…1,[4][5][6] It should also be remarked that these reported ICPs were examined only in radially viewing ICP-OES. 1,[4][5][6] In the present study, we found an effective sensitivity enhancement of elements in axially viewing ICP-OES by adding N2 gas into the Ar plasma gas. This is the first report concerning an examination of a mixed-gas ICP in axially viewing ICP-OES.…”