Evaluation of various nebulizers for use in microwave induced plasma optical emission spectrometry

Abstract

Three different micronebulizers, the micro3 (M3), the flow focusing pneumatic nebulizer (FFPN) and the microcapillary array nebulizer (NAR-1), were compared with a conventional Meinhard pneumatic concentric nebulizer (PN) working at low liquid flow rates for the elemental analysis of liquid samples by microwave induced plasma optical emission spectrometry (MIP-OES). Three nebulizers (M3, FFPN, PN) were operated in conjunction with the same cyclonic spray chamber. A critical evaluation has been carried out of the nebulization stages, such as the formation of the primary and tertiary aerosol, separation of large droplets (drop size distribution) in the spray chamber (also evaluated for the NAR-1 nebulizer) and aerosol transport to the plasma torch. Atomic emission was measured for Ba, Ca, Cd, Cu, Fe, I, Mg, Mn, Pb, Sr and Zn. Analytical performance of the nebulization systems were characterized by determination of the limits of detection (LODs), the precision (RSDs) and the memory effects (wash-out time) for these elements, and ranged between 0.004–0.099 μg mL⁻¹, 4–8%, and 5–7 minutes, respectively. Analysis of certified reference materials (TORT-1, Human Hair No. 13, Lichen IAEA-336, Soya Bean Flour INCT-SBF-4) were performed to determine the accuracy and precision available with the presented nebulization systems. These materials were microwave/nitric acid digested and analyzed by calibration with synthetic solutions of the analytes. In general, the results indicated that the FFPN nebulizer gave rise to higher emission signals and slightly lower LOD values than the other three nebulizers. The nebulizers exhibited no clogging problems.