Flame Emission Spectroscopy
Definition and meaning of Flame Emission Spectroscopy in chemistry.
Flame emission spectroscopy (FES) is an analytical technique that measures the light emitted by atoms excited in a flame to determine the concentration of a metal element in a sample.
In more detail
A sample solution is aspirated into a flame, where heat vaporizes it and promotes some atoms' outer electrons to higher energy levels; as these electrons fall back to the ground state, they emit light at wavelengths characteristic of the element, such as sodium's bright yellow line at 589 nm. The intensity of this emitted light is proportional to the concentration of that element, so it can be quantified against calibration standards of known concentration. FES works best for elements with low excitation energies, especially alkali metals and alkaline earth metals. Simple filter-based versions of this instrument are often called flame photometers.
Key facts
| Field | Analytical Chemistry |
|---|---|
| Also called | Flame photometry |
| Best suited for | Alkali and alkaline earth metals (Na, K, Li, Ca) |
| Sodium emission line | 589 nm (yellow) |
A clinical laboratory uses flame photometry (FES) to measure sodium and potassium concentrations in a patient's blood serum sample.
Frequently asked questions
How does FES differ from atomic absorption spectroscopy (AAS)?
FES measures light emitted by atoms that have been thermally excited by the flame, whereas AAS measures light absorbed by ground-state atoms from an external lamp. AAS is generally more sensitive for elements that are not easily excited at flame temperatures.
Why is FES limited mainly to certain metals?
Only elements with relatively low excitation energies, such as sodium, potassium, lithium, and calcium, are efficiently excited by ordinary flame temperatures, so FES is not practical for most other metals without hotter excitation sources.