been established as an effective technique in regular use. This group of elements includes, Hg, As, Se,
Sb, Te, and Bi which can be determined at concentrations of 0.1 ppb or less. Hg and Cd can be
determined as organoderivatives. In the case of mercury, alkyl derivatives are of considerable
environmental significance and these may be determined after prior chromatographic separation. Figure
8.31 shows the typical construction of an AFS detector for the measurement of these volatile elements
and compounds. Reduction of the analytes is carried out by the action of tin(II) chloride or sodium
borohydride as in AAS methods (page 330).
Figure 8.31
Schematic representation of an AFS detection system for
the determination of elements in the form of volatile
hydrides (PMT = photo-multiplier tube). (With permission
of PS Analytical Ltd)8.8—
X-ray Emission Spectrometry
Summary
Principles
Characteristic X-rays emitted from transitions involving K and L electrons; wavelength and emission
intensity measurements for qualitative and quantitative elemental analysis respectively.
Instrumentation
Excitation of sample by bombardment with electrons, radioactive particles or 'white X-rays'. Dispersive
crystal analysers dispersing radiation at angles dependent upon energy (wavelength), detection of
radiation with gas ionization or scintillation counters. Non-dispersive semiconductor detectors used in
conjunction with multichannel pulse height analysers. Electron beam excitation together with scanning
electron microscopes.