Detection of metals by flame atomic spectrometric methods

7 Detection of metals by flame atomic spectrometric methods 

Most modern laboratories are nowadays equipped with flame atomic spectrometers, which are routinely used for the quantitative determination of metals in solution. If such equipment is available, detection of metals can be carried out much faster than with the usual wet tests, especially if separations are involved. Usually 1-2 ml solution is consumed during one test however in most cases the tests are so sensitive, that a portion of the original sample solution can be diluted 10-100 fold, leaving enough material for separations. Note that flame atomic spectrometric tests do not provide information about the oxidation state of the metal (e.g. they cannot differentiate between divalent and trivalent iron, trivalent or hexavalent chromium, etc.).  

It is important to emphasize some aspects of safety. Cylinders of fuel and oxidant gases must be fastened to a wall or laboratory bench. The exhaust gases have to be channelled through an adequate ventilation system and released into the atmosphere. In some cases (e.g. when employing nitrous oxide) the exhaust gases are toxic. Special care has to be exercised when lighting and extinguishing the flame. 

In the present text only brief outlines of these methods can be presented. For more detailed discussion of the theoretical principles, instrumentation and practice of atomic spectrometry, modern texts of instrumental analysis should be consulted, e.g. Daniel C. Harris Quantitative Chemical Analysis, 3rd edn, W. H. Freeman and Co, 1991, chapters 20 and 21. 

There are two principal methods available, which require somewhat different instrumentation these will be described below. Historically, atomic emission instruments were designed first one can find such older instruments in many laboratories. Nowadays atomic absorption spectrophotometers are more popular, these however can be used also in emission mode. 

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