Impact of membrane desolvation on the effects of sodium on response in inductively coupled plasma atomic emission spectrometry with ultrasonic sample introduction

Abstract

This report compares the influence of sodium on response with ICP-AES for copper, cadmium, lead and cobalt with ultrasonic sample introduction in the presence and absence of a microporous membrane desolvation (MMD). Comparisons are reported at viewing positions of 8, 14, and 20 mm above the load coil, for injector gas flow rates of 0.70, 0.85 and 1.00 l min^–1, and at sodium concentrations ranging from 0.00 to 0.08 M Na. Blank emission intensities were depressed in the presence of sodium regardless of the operating condition(s). Depressions in the blank emission intensities were greater without the MMD, but were less than 20%. The magnitude of depression in the blank emission intensities did not vary significantly among the analyte lines or with the viewing position. The impact of sodium on signal intensities with and without the MMD was greater than the impact on the blank emission intensities, with changes approaching 150%. At the lower viewing positions, signal enhancement in the presence of sodium was common and the degree of enhancement was greater with the MMD. Response changes with respect to sodium concentration were also different with and without the MMD low in the plasma. Higher in the plasma, element-to-element variation occurred in the nature of the impact of sodium. For signals that were enhanced, the degree of enhancement was generally greater with the MMD, but when signals were depressed, there was no correlation to the presence or absence of the MMD. In contrast to the lower viewing position, higher in the plasma response changes with respect to the sodium concentration were similar. These results suggest that although the plasma is physically different with and without the MMD, the MMD does not alter the mechanism(s) by which sodium impacts response.