MICROFLOW ULTRASONIC NEBULIZER FOR INDUCTIVELY-COUPLED PLASMA-ATOMIC EMISSION-SPECTROMETRY

A novel microflow ultrasonic nebulizer (mu-USN) gives stable nebulization at microliter per minute flow rates. A very localized aerosol generation point is formed by feeding liquid through a 50-mum diameter fused silica capillary tube onto the surface of an ultrasonic transducer, using a liquid chromatography pump. At very low flow rates (5-10 muL/min), the aerosol generated has an extremely low Sauter mean diameter (2 mum) and analyte transport efficiencies are close to 100%. This is the first time to the authors' knowledge that such efficient continuous nebulization at very low flow rates has been reported, other than through the use of the electrospray technique. Generally good stability, precision, and reproducibility were observed for Mn emission signals at all flow rates. Experimental detection limits with the mu-USN observed at 10 muL/min flow rate without desolvation are comparable to those obtained with a standard pneumatic nebulizer operated at 1 mL/min, although the analyte mass transport rate to the plasma for the pneumatic nebulizer is estimated to be approximately 1.9 times higher than that for the mu-USN. The mu-USN therefore gives greater conversion efficiency of analyte to useful atomic and ionic emission from the plasma, as a consequence of smaller particle size and lower aerosol solvent loading. At flows less-than-or-equal-to 10 muL/min, solvent loading in the plasma is sufficiently low to make desolvation unnecessary. The ability to provide essentially 100% transport efficiency at flow rates in the range of 5-20 muL/min suggests good potential for mu-USN use in interfacing ICPAES and ICP/MS with capillary electrophoresis and microcolumn liquid chromatography. In addition to use with plasma emission spectrometry, the technique should also be readily applicable to inductively coupled plasma mass spectrometry and microwave emission spectrometry.