What is a Flame Photometer?
Fast, efficient results in moments
When Robert Bunsen and his assistant Peter Desaga invented his clean flame burner in the mid-18th century, it was for the purpose of spectral analysis or atomic spectroscopy. The colourless flame allowed Bunsen to reveal two new elements (caesium and rubidium), among his many other important contributions to science.
Gas Chromatography and Spectroscopy are revealing of extremely fine details in analysis but they are time-consuming, grossly overpowered, and expensive processes for many day-to-day applications in continuous or frequent analysis. They require consumables such as diffusion columns and high levels of maintenance.
This is where the hyper-efficient field of Flame Emission Spectroscopy (FES), or more commonly, Flame Photometry, comes to the rescue. The process can be human-powered for infrequent testing or fully automated for continuous process monitoring.
A flame photometer uses a spectroscope for isolating and identifying quantities of inorganic elements, particularly in biological environments, such as hospitals and the food industry. By introducing an unknown test substance via a neutral/known liquid carrier to a stable colourless flame, characteristic visible spectral light is emitted. The spectral lines for each substance are unique to that substance, and the intensity of each line indicates precisely how much of a substance is present in a given sample.
This allows the rapid identification of the Group I and Group II alkaline/alkaline earth metals including Sodium, Potassium, Lithium, Barium and Calcium (and occasionally others, depending on process and equipment).
Isolating these metals is very important in blood chemistry analysis, for example, or for the detection of the presence and the quantification of nutrients in food products. Pharmacology often uses flame photometry as one phase of their quality control for their products.
How Does It Work?
Fuel and air are mixed in a very controlled way to produce the “ideal flame” as Bunsen intended while being fed with atomised distilled water. Various control samples are introduced to allow adjustment of the machine to its most accurate “zero” state. The test sample is then introduced and the dissolved or suspended metal is disassociated by the heat of the flame (thermal excitation) into discrete ionic atoms which then move their valance electrons up to the next higher energy level where they are not stable.
This is caused by the absorption of photons. As the atoms decay to their normal lower energy state, they emit photons, generating a characteristic colour for the element being investigated. The light can be analysed with either absorption techniques or emission techniques, depending on the need and device design.
Typically you will see colours in the actual flame itself such as violet for potassium, green for barium, red for lithium, yellow for sodium, and so on. The flame is generally visible to the investigator, and it is useful to monitor it for anomalies.
The greatest advantage of flame photometry is that samples with mixed contents will produce the combined spectrum of all the substances, which can then be recognised individually. As previously stated, the intensity of each line set also indicates their individual concentrations. The upper image contains the two metals shown beneath it once the emission lines are separated.
Flame Photometry is fast and efficient. Units can be used with individual human testers for rapid assessment or can be fully automated to continuously test samples in a process, eliminating the necessity for a human attendant.
They are also extremely economical to operate, needing only clean fuel, an air compressor, and the unit itself. Low maintenance requirements make flame photometry an excellent choice for analytical needs.