A MICROWAVE POWERED THERMOSPRAY NEBULIZER FOR LIQUID SAMPLE INTRODUCTION IN INDUCTIVELY-COUPLED PLASMA-ATOMIC EMISSION-SPECTROMETRY

A new thermospray nebulizer based on the absorption of microwave radia tion (MWTN) by aqueous solutions of strong acids is presented for the first time, To this end, a given length of the sample capillary is pla ced inside the cavity of a focused microwave system. A small piece of a narrower capillary tubing is connected at the tip of the sample capi llary, outside the microwave cavity, to build up pressure, Drop size d istributions of primary aerosols are exhaustively measured in order to evaluate the influence of several experimental variables (microwave p ower, liquid now, irradiation length, inner diameter of the outlet cap illary, nature and concentration of the acid) on the characteristics o f the primary aerosol that are related to the emission signal. These e xperiments have been performed mainly to increase our understanding of the microscopic process of this new type of aerosol generation. A sta ndard Meinhard nebulizer was employed for comparison, Under the best c onditions the entire aerosol volume is contained in droplets smaller t han 20 mu m compared with 45% of the volume of tile aerosol generated by the Meinhard, Hence, higher analyte and aerosol transport rates are to be expected for the MWTN compared with the Meinhard nebulizer. As any highly efficient nebulizer, MWTN requires a desolvation unit, For solutions 0.75 M in strong acid, the new nebulizer improves sensitivit y (1.0-2.8 times), limits of detection (1.2-3.0 times), and background equivalent concentration (0.9-2.0 times) as compared to the standard Meinhard nebulizer, features many of the advantages of the conventiona l thermospray nebulizer, and overcomes some of its drawbacks (MWTN doe s not show corrosion problems and works at lower pressure, the aerosol characteristics are not modified when the PTFE capillary is replaced) .