Page 160 - An Introduction to Analytical Atomic Spectrometry - L. Ebdon

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7
Special Sample Introduction Techniques

In addition to conventional aspiration, using a nebulizer and spray chamber, samples may be introduced
in to atomic spectrometers in a number of different ways. This may be because a knowledge of
speciation (i.e. the organometallic form or oxidation state of an element) is required, to introduce the
sample while minimizing interferences, to increase sample transport efficiency to the atom cell or when
there is a limited amount of sample available.

7.1 Pulse Nebulization

For samples that are limited in volume, that contain high dissolved solids or large amounts of organic
solvents that may theoretically cause spectroscopic interferences, pulse nebulization (a very basic form
of flow injection) may be used. This procedure permits the use of smaller samples (25-200 mm ) and
3
higher concentrations (e.g. 10% w/v steel) than in normal nebulization. A cup, made of Teflon or other
suitable plastic, is attached to the nebulizer tube, and the sample pipetted into the cup using a micro-
pipette. The sample is totally consumed and a peak signal is observed. For example, the technique may
be used for steel analysis or in a biological study where only a small amount of sample is available. The
technique also enjoys a number of alternative names: discrete sample nebulization, gulp sampling,
direct-injection cup nebulization, and Hoechst cup nebulization. The technique has been used mainly
for sample introduction to flame spectrometry.