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magnesium nitrate, which thermally decomposes to magnesium oxide and in the process traps analyte
atoms within its crystalline matrix, thermally stabilizing them until approximately 1100°C, and
ammonium phosphate, which stabilizes volatile analytes such as cadmium. Organic acids such as
ascorbic, citric and oxalic acid have also been used as reducing agents for analytes such as lead. Often,
a combination of modifiers is used. One of the most common combinations is that of magnesium nitrate
and palladium nitrate. This has been termed the universal modifier because of its use for a large
number of analytes.

3.6.5 The STPF Concept

The stabilized temperature platform furnace (STPF) concept was first devised by Slavin et al. It is a
collection of recommendations to be followed to enable determinations to be as free from interferences
as possible. These recommendations include (i) isothermal operation; (ii) the use of a matrix modifier;
(iii) an integrated absorbance signal rather than peak height measurements; (iv) a rapid heating rate
during atomization; (v) fast electronic circuits to follow the transient signal; and (vi) the use of a
powerful background correction system such as the Zeeman effect. Most or all of these
recommendations are incorporated into virtually all analytical protocols nowadays and this, in
conjunction with the transversely heated tubes, has decreased the interference effects observed
considerably.

Q. What are the advantages of transversely heating the graphite tube?

Q. Why is isothermal operation recommended for overcoming interferences?

Q. Explain why matrix modification may lead to more efficient matrix removal.

3.7 Other Electrothermal Techniques

The interest in the graphite furnace as an emission source stems from the desire to achieve a multi-
element detection capability whilst retaining the low limits of detection and the possibility of sample
pretreatment. Several