Figure 8.30
Platform shape and orientation within a furnace tube.identical to that of a graphite furnace. The absolute sensitivity of flameless atomizers is very high, as
little as 10–^14 g for volatile elements such as zinc, magnesium and cadmium, but relative sensitivities are
only marginally better than those obtained by flame vaporization because the sample size is much
smaller (Table 8.4).
Vaporization by Reduction and Hydride Generation
In a limited number of cases an element or one of its compounds is sufficiently volatile for it to be
separated from the matrix and introduced into the light path without the use of a nebulizer or
electrothermal atomizer. Mercury is a unique metal in that it has a significant vapour pressure at room
temperature. Furthermore, the vapour is monatomic and unreactive. Thus it may be entrained in a gas
stream and measured by the atomic absorption of this cold vapour. A typical analytical method would
first involve the use of an oxidizing mixture such as sulphuric acid and potassium permanganate to
destroy organic matter. The mercuric sulphate thus produced is then reduced with stannous chloride to
produce mercury vapour, which is swept through a narrow quartz cell about 15 cm long with a diameter
of about 0.75 cm. In some methods the vapour is swept straight through the cell giving a transient
absorption peak similar to that produced by electrothermal vaporization. Alternatively, the vapour may
be circulated in a closed loop leading to a stable signal when all the mercury has been volatilized into
circulation. Other methods involve collection as a gold or copper amalgam prior to measurement.
Elements such as antimony, arsenic, bismuth, germanium, tin, selenium, tellurium and lead, although
not volatile in the elemental form, have volatile hydrides. At different times a variety of strong reducing
agents has been used to produce these hydrides, but sodium borohydride is generally accepted as the
most suitable reagent. Wet oxidation to destroy organic material is a common prerequisite for the
production of the hydrides. The formation of some hydrides is comparatively slow and the best
sensitivity