Page 89 - An Introduction to Analytical Atomic Spectrometry - L. Ebdon

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pipetting is used. It cannot be expected that discrete signals can offer precision similar to that of
integrated continuous signals. It should be noted that the precision for electrothermal atomization is
typically 5% compared with 2-3% from a flame or plasma instrument.

(iii) Interferences: Electrothermal atomizers still suffer from more interferences than the nitrous oxide-
acetylene flame. These interferences, however, have been reduced substantially over the last 10 years.

(iv) Expense: a good electrothermal atomizer with autosampler is an expensive instrument, costing
£50,000-60,000, whereas a simple, very basic, flame spectrometer may cost as little as £10,000 (more
normally £15,000-20,000). An ICP-AES instrument will cost in excess of £60,000 and ICP-MS
instrument between £150,000 and £250,000.

(v) Complicated programmes: optimizing the conditions of electrothermal atomization is far more
complicated than for a flame. ICP-AES and ICP-MS are more complicated instruments to operate per
se, although it is easier to find compromise operating conditions.

(vi) Small samples: the small samples necessary in electrothermal atomization present problems in
sample handling and with homogeneity.

(vii) Single element: traditionally it has only been possible to determine one element at a time, whereas
ICP-AES and ICP-MS are simultaneous multi-element techniques. However, new multi-element
spectrometers are now available.

While it is to be expected that the effects of these disadvantages will continue to diminish as more
becomes known about electrothermal atomization, currently it can be said that if there is sufficient
sample for flame or ICP analysis, and that these techniques offer sufficient sensitivity, then they should
be used in preference. Plasma techniques should be used in preference to the flame if more than one
analyte is to be determined. Recently a multi-element, simultaneous electrothermal instrument has been
developed. These spectrometers still use a suite of hollow cathode lamps as sources. At present, a
maximum of six analytes can be determined simultaneously. This area is likely to expand very rapidly,
which may lead to a resurgence in the technique. If the sensitivity of a flame or ICP-AES is insufficient,
and ICP-MS cannot be afforded, electrothermal atomization comes into its own, and is invaluable when
either high sensitivity is required or when only small amounts of sample are available.

Q. What are the particular advantages of electrothermal atomization?

Q. Would you use electrothermal atomization or some other technique for the following determinations:
(1) zinc in a trade effluent at the 0.1 µg ml level; (2) cadmium in blood at the ng ml level; (3) lead in
-1
-1
steel at (a) the 0.1% w/w level and (b) the 0.001% level?