Use of an ultrasonic nebulizer with membrane desolvation for analysis of volatile solvents by inductively coupled plasma atomic emission spectrometry

Abstract

The petroleum and chemical industries need a rapid, and sensitive technique for the trace analysis of volatile feedstocks, intermediates and products, including high-purity solvents. Organic solvent loading of the inductively coupled plasma (ICP) adversely effects the application of ICP atomic emission spectrometry to analysis of volatile organic liquids when conventional sample introduction equipment is employed. The use was investigated of a membrane separator as a secondary desolvation device used with an ultrasonic nebulizer (USN) to further reduce organic vapour loading of the plasma and enable µg l–1 determinations to be performed on solvents and petroleum products boiling well below 100 °C. Two prototype membrane desolvator units and the final commercial unit were tested on a variety of materials including hexanes, methanol, tetrahydrofuran, acetone and dichloromethane. Organic vapour removal was efficient enough to permit the analysis of these materials at ‘normal’ sample introduction rates (1–4 ml min–1) and practical operating conditions. Detection limits similar to aqueous solution USN limits were achieved. Owing to the near complete solvent matrix removal provided by the USN-membrane sample introduction system, ‘universal calibration’ of the ICP should be possible at certain ICP operating conditions. Experiments were conducted with the goal of achieving a single calibration valid for a variety of volatile organic solvents. Accurate calibration was maintained for several diverse solvent types after applying corrections for solvent nebulization efficiencies relative to the calibration solvent.