Section E – Spectrometric techniques
E4 FLAME ATOMIC EMISSION
SPECTROMETRY
Principles When the salts of some metals are introduced into a flame, they impart charac-
teristic colors to it. For example, sodium salts give an intense yellow-orange
color. This is the basis of the ‘flame test’ used in qualitative analysis. The
thermal energy of a gas-air flame is quite low, since the temperature is usually
less than 2000 K and only those transitions of low energy are excited.
Early atomic emission instruments used electric arc or spark excitation. The
higher energy of these sources produced a very great number of emission lines
throughout the visible and UV regions. However, simultaneous measurement of
a large number of elements was possible.
With flame excitation, electronic transitions in alkali and alkaline earth
metals, as listed in Table 1are the most important.
Key Notes
When the atoms of samples are excited to higher electronic energy levels
in flames they emit radiation in the visible and UV regions of the
electromagnetic spectrum. Emission intensities may be measured to
analyze for metals, especially alkali and alkaline earth elements.A flame atomic emission spectrometer or flame photometer incorporates
a burner, monochromator, or filters, a detector and a method of
introducing the sample solution into the flame.The technique is used primarily for the quantitative determination of
alkali and alkaline earth metals in clinical, biological and environmental
samples.Related topics Inductively-coupled plasma Atomic absorption and atomic
spectrometry (E5) fluorescence spectrometry (E7)PrinciplesInstrumentationApplicationsTable 1. Flame excited lines of some metals
Metal Wavelength/nm Color
Lithium 670 Red
Sodium 589 a Orange–yellow
Potassium 766 a Red
Rubidium 780 a Dark red
Magnesium 285 UV
Calcium 622 b Orange
Strontium 461 Red
Barium 554 Green
Thallium 535 Green
Copper 513 Green
aThese lines are doublets. bThis line is due to emission from a calcium hydroxide band.