Elemental matrix effects in ICP-AES

Axially and radially viewed inductively coupled plasmas — a critical review

Inductively Coupled Plasma Atomic Emission Spectroscopy

Fundamental studies of mixed-gas inductively coupled plasmas

An evaluation of ion-atom emission intensity ratios and local thermodynamic equilibrium in an argon inductively coupled plasma

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.

A Critical Comparison of Ar and Ar-N 2 Inductively Coupled Plasmas as Excitation Sources for Atomic Emission Spectrometry

A convenient and a rapid technique is introduced to estimate the electron number densities, ne, in inductively coupled plasmas. The method is based on previously reported observations that the principal quantum number of the last discernible line in a series limit depends on ne. The spatially integrated ne values, as determined from the spectra of H, Li, Mg, Al, Ca, and K emitted in a pure Ar plasma ranged between ∼4 × 1014 and ∼3 × 1015 cm−3 for various forward powers and observation heights. These results agreed with ne values derived from other methodologies such as the Stark broadening and absolute continuum intensity.

Electron Number Densities in Analytical Inductively Coupled Plasmas as Determined via Series Limit Line Merging

The emission spectrum of the series limit of Al was used to estimate the electron number densities (ne) in inductively coupled Ar or Ar-N2 plasmas (ICP). The spectra of the series limit were recorded either with a silicon-intensified target vidicon detector or by a computer-controlled, scanning spectrometer. Background stripping was performed on the spectra recorded by both instruments to enhance signal recovery. Under comparable experimental conditions, the ne values in the Ar-supported ICP were higher than those observed in Ar-N2 plasma, when pure N2 was used in the outer flow. However, the ne value of the Ar ICP under the conditions commonly used in analytical laboratories (15 mm observation height and 1200 W forward power) was comparable to that found in pure N2 outer flow, Ar-N2 plasmas operated under conditions (5 mm observation height and 3000 W forward power) suitable for exciting spectral lines of high excitation energies. Whereas the use of higher, carrier gas flows tended to reduce the ne values of the Ar ICP substantially, this trend was not observed for the pure N2 outer flow Ar-N2 plasma.

Electron Number Density Measurements in Ar and Ar-N2 Inductively Coupled Plasmas

A skimmer located below the usual observation height of an inductively coupled plasma (ICP) allows the axial channel region of the ICP to flow through the central hole of the skimmer while the outer Ar flow is deflected. Signal-to-background (S/B) ratios and the estimated detection limits measured immediately above the skimmer were generally 5 to 20 times superior to the best results obtained by the conventional ICP system. The highest S/B lines possessed wavelengths greater than 300 nm. Matrix effect studies on the Ca-PO4 and the Ca-Al systems revealed that the skimmed plasma was as free of vaporization-atomization interference as the conventional plasma, but easily ionizable elements produced a greater level of suppression/enhancement effects. Electron number densities, as determined via the series limit line merging technique, were lower in the skimmed plasmas as compared with the conventional ICP's.

Akbar Montaser

Papers

A Critical Comparison of Ar and Ar-N 2 Inductively Coupled Plasmas as Excitation Sources for Atomic Emission Spectrometry

Electron Number Densities in Analytical Inductively Coupled Plasmas as Determined via Series Limit Line Merging

Electron Number Density Measurements in Ar and Ar-N2 Inductively Coupled Plasmas

Atomic Emission Spectrometry with a Skimmed Inductively Coupled AR Plasma