Effect of droplet size on the phosphine depression of calcium atomic emission signals in flame spectrometry

Abstract

The effect of the droplet size on the magnitude of the phosphine depression of calcium signals is discussed. The droplet size governs the time required for droplet desolvation in the flame. It is during the desolvation process that the combustion products of phosphine, PO x , diffuse into the droplet and form a refractory compound with the analyte. The longer the desolvating droplet resides in the PO x -contaminated flame, the more severe the depression. A uniform droplet generator, a pneumatic nebulizer spray chamber system, and a glass-frit nebulizer spray chamber system were the sample introduction systems studied. Droplet sizes of (55 μm, 0.5–10 μm (2 μm mean), and <0.1–2 μm (0.1 μm mean) were produced by these systems, respectively, and depressions of the calcium signals of 57%, 55%, and 4% were noted. These results suggest that the phosphine depression on calcium signals may be alleviated by using a glass-frit nebulizer (or modifying a commercial nebulizer) to remove droplets greater than 2 μm in diameter.