Flame photometry and flame emission spectroscopy compared
Although in principle quite similar, flame photometry and flame emission spectroscopy each offer specific advantages and find their own place on the analytical laboratory bench. Where the flame emission spectroscope offers the potential for more detailed analysis of a wider range of samples, the flame photometer provides a robust and economical instrument to determine the presence of concentration of several common elements found in industrial and pharmaceutical processes.
Flame photometers are most commonly used to detect and quantify the presence of the alkali metals lithium (Li), sodium (Na), and potassium (K), and the alkali earth metals calcium (Ca), and barium (Ba). Rubidium (Rb), caesium (Cs), and strontium (Sr) are also readily detectable by this method.
Because these elements emit light (photons) within the visible range at relatively low temperatures, an inexpensive heat source – propane, butane, or natural gas – can be used to excite them. Typical flame photometry operations ‘burn’ the sample at 1500-2000 °C. Sample preparation is straightforward, involving making the sample completely aqueous using deionised water before introducing it the flame photometer. The photodetector records and measures the resulting radiation, and the digital display provides a readout of element concentration to within 0.5%. Usual laboratory practices must be adhered to, especially in maintaining the cleanliness of the sample and the diluent, to obtain reliable results.
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