High-temperature flame photometry

This article focuses primarily on traditional low-temperature flame photometry. High-temperature flame photometry has evolved into separate techniques, typically identified by their temperature sources (e.g., inductively coupled plasma-atomic emission spectrometry, ICP-AES ). Some references to other related analytical tools, including high-temperature flame photometry, are made here to establish perspective. 

The ratio, Nj/N0, can therefore be calculated. For the relatively easily excited alkali metal sodium, it is 9.9 x 10 6 at 2000 °K and 5.9 x 10 4 at 3000 °K this latter temperature is about the highest commonly obtained with flames used for atomic absorption or emission work. Hence, only about 1(T3 % of the sodium atoms are excited at 2000 ° and 6 x 1(F2 % at 3000°. For an element such as zinc,Nf/N0 is 5.4 x 10"10 at 3000 and so only 5 x 10"8% is excited. In spite of the small fraction excited, good sensitivities can be obtained for many elements by flame photometry if a high temperature flame is used, because the difference between zero and a small but finite number is measured. For example, seventy elements can be determined by flame photometry using the nitrous oxide-acetylene flame 1H. 

Flame photometry is the name given to the technique that measures the intensity of the light emitted by analyte atoms in a flame. It is the oldest of all the atomic techniques. It is not highly applicable because of the low temperature of the flame. Only a handful of elements can be measured with this technique, including sodium, potassium, lithium, calcium, strontium, and barium. The technique was formerly used... 

Atomic absorption spectroscopy is highly specific and there are very few cases of interference due to the similar emission lines from different elements. General interference effects, such as anionic and matrix effects, are very similar to those described under flame emission photometry and generally result in reduced absorbance values being recorded. Similarly, the use of high temperature flames may result in reduced absorbance values due to ionization effects. However, ionization of a test element can often be minimized by incorporating an excess of an ionizable metal, e.g. potassium or caesium, in both the standards and samples. This will suppress the ionization of the test element and in effect increase the number of test atoms in the flame. 

With the use of fuels that produced hotter flames, earlier flame photometers became useful for analyzing elements beyond the alkali and alkaline earth metals. The development of atomic absorption spectrophotometers in the late 1960s provided the analytical chemist with a better tool for many of these applications. Later developments in high-temperature flame photometry narrowed the analytical applications of low-temperature flame photometry even further. The utility of the flame photometer to the clinical chemist, however, was not diminished until the development... 

Atomic spectroscopy can be divided into several broad classes based on the nature of the means of exciting the sample. One of these classes is generally known as atomic emission spectroscopy, in which excitation is thermally induced by exposing the sample to very high electric fields. Another class is known as flame emission spectroscopy or flame photometry, in which excitation is thermally induced by exposing the sample to a high-temperature flame. These methods differ from atomic absorption spectroscopy, in which the absorption of light from a radiation source by the atom is observed rather than the emission from the electronically excited atom. 

DOC analysers on the market at the time of purchase, operate based on two different principles A) high temperature oxidation over a catalyst followed by measurement of the evolved CO 2 by infra-red photometry, or after conversion to methane, by flame ionisation detection, and B) wet oxidation of organic carbon by the action of UV light in the presence of potassium persulphate. The CO2 produced is stripped from solution and reduced to methane which is measured quantitatively by flame ionisation detection. 

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