Characterization of and Correction for Memory Effects Produced by Pneumatic Nebulizers in Inductively Coupled Plasma Emission Spectroscopy

Abstract

Memory effects or sample carry over characteristics of five pneumatic nebulizers routinely used for sample introduction into plasma emission spectrometers are studied. It is observed that the primary source of the memory noted for the nebulizers studied is the dissipation rate of the fog produced by the nebulizer during introduction of the previous sample or samples. Contributions to memory from the aspiration tube, salt deposition at the nebulizer tip, and a chromatographic effect at the torch tip are minimal. In terms of operational stability, detection capability, tolerance for particulates, and low memory, a concentric nebulizer with a Pt: Ir needle, Teflon nose cone, and an extended spray director is superior to the others tested. Even under the most optimum conditions, the washout time required to reduce sample emission to 0.1% of its maximum intensity varies from 2 to 4 min, thereby greatly increasing per sample analysis time. The memory effect phenomena can be accurately modeled by a hyperbolic curve and can, therefore, be easily corrected for in routine analysis. The memory correction value, which is subtracted from a sample's net emission intensity, is calculated from the product of an empirically defined correction constant and the emission intensity of previously run samples divided by the washout time. Examples of the utilization of the correction are shown.