Characterization of a 23-mm Torch for Use in Inductively Coupled Plasma Mass Spectrometry

Abstract

A 23-mm-i.d. torch is described and evaluated for use in inductively coupled plasma mass spectrometry. The plasma operates optimally at 1.50 kW forward power and 19.2 L/min total argon flow. The effect of the customary operating parameters (nebulizer flow rate, rf power, sampling depth, and ion-lens voltages) on analyte signals is discussed. Detection limits, oxide-ion ratios, and doubly charged ion ratios have been measured and are compared with those produced by an 18-mm-i.d. low-flow MAK torch. When compared to the conventional torch, the 23-mm system exhibits comparable detection limits for low-mass ions but better detection limits for high-mass ions (Pb and U). Oxide-ion ratios are lower in the larger torch, but doubly charged ion ratios are higher. Because optimal sampling depths in the larger torch are higher, entrained air in the tail flame causes instability and results in increased ArO⁺ and ArN⁺ background signals.

Keywords

Inductively coupled plasma mass spectrometry 23-mm torch Torch design

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