Page 79 - An Introduction to Analytical Atomic Spectrometry - L. Ebdon

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the nature and extent of interferences may vary in different types of atomizers. We shall now consider
the problems encountered in the furnace type atomizers used in AAS.

3.5.1 Physical Interferences.

The steep thermal gradient along the tube means that any variation in the sample position (e.g.
because of pipetting, or spreading due to surface tension and viscosity effects) will alter the atomization
peak shape. Peak area integration will help to minimize this problem, as will a rapid heating ramp and
isothermal operation (see Sections 3.6.2 and 3.6.3).

3.5.2 Background Absorption

As already noted, the effects are usually severe. Large amounts of matrix are volatilized in a confined
space. Molecules may exhibit absorption spectra in the region of interest; this is especially true of
alkali metal halides. Particulate smoke also contributes to this problem. Light emission from the
incandescent walls may further distort the baseline. Every effort should be made to reduce background
absorption effects in method development, e.g. by attempting to reduce the matrix during the ash stage.
Background correction should be applied routinely (see Section 2.2.5.2), remembering that
background absorption is often at the 90% level.

3.5.3 Memory Effects

Incomplete atomization of involatile elements can sometimes cause a problem. Often this can be
overcome by firing a so-called 'cleaning' cycle at maximum power between analytical cycles.

3.5.4 Chemical Interferences

3.5.4.1 Losses of Analyte as a Volatile Salt

This is particularly likely to occur when halides are present, at the ashing or atomizing stage at
temperatures too low to afford atomization, and can lead to losses of, for example, CaCl or PbCl . The
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use of hydrochloric acid for sample dissolution should be avoided. If chloride is present, excess nitric