Page 106 - An Introduction to Analytical Atomic Spectrometry - L. Ebdon

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Figure 4.7 (continued)

which is immersed in the solution to be nebulized. The drop in pressure causes the solution to be drawn
up the tube and shattered into droplets. The main disadvantage of these nebulizers is that they can only
tolerate solutions containing less than 0.1-1% dissolved solids.

The solution to be nebulized is usually pumped to the nebulizer using a peristaltic pump, unlike for
FAAS, where the solution uptake is by free aspiration. The solution is pumped through polymeric
tubing [usually poly(vinyl chloride)] and also connecting tubing (usually Teflon) to the nebulizer. Both
of these materials can be manufactured to a high degree of purity, hence contamination is minimized.
The solution is pumped at a rate of 1-2 ml min , which is much slower than the 5-10 ml min uptake
-1
-1
rate for FAAS. This tends to favour the formation of fewer but smaller droplets, which results in less
noise but a lower overall sample transport efficiency.
Glass frit (Fig. 4.7c) and grid-type (Fig. 4.7d) nebulizers operate by running the sample over a glass
frit or metal grid, respectively. The nebulizer gas passes through the frit or grid at high velocity,
shearing the sample solution into fine droplets. Such nebulizers have greater transport efficiency than
pneumatic nebulizers owing to the very fine droplets produced, although they also suffer from salt
deposition if solutions containing high dissolved solids are aspirated.