Empfindlichkeitssteigerung der atomaren Absorptionsanalyse mittels flammenloser Atomisierung

Abstract

After a brief discussion of the basic principles of atomic absorption analysis, the disadvantages of the flame as atomizer and absorption cell are outlined. Some flameless atomization methods previously published, namely hollow cathode sputtering (Walsh), thermic atomization in a high temperature furnace (L’vov), and sample boat technique (Kahn et al.) are reviewed.
In contrast, the author’s approach incorporates an isolation step. The metal of interest is coated onto a wire and released as an atomic vapor in the beam of an absorption spectrometer by heating the sample wire with an electric current. This is particularly simple for the analysis of mercury in solution. The metal is sampled by spontaneous amalgamation or electrolysis on copper, and the atomic vapor released in an absorption cell. The concentration of mercury in solution is calculated from the absorption, by the vapor cloud, of a mercury resonance line.
Other metals can also be determined with the same approach, provided that they can be deposited on a sample wire and released as a mono-atomic vapor. So far, experiments have been successful with cadmium, zinc, lead, thallium, copper, silver, gold and platinum. In these cases, a platinum or tungsten sampling wire must be used. A “free sample wire” and an “enclosed sample wire” method are described. In the former, a coated platinum spiral is placed in the light beam of the spectrometer without using a cell. The absorption signal is produced mainly by the vapor within the heated spiral. In the latter, the coated sample wire (tungsten can be used) is placed in a silica cell before atomization. An argon atmosphere is recommended. Both techniques require a fast recording system, since the vapor cloud diffuses and condenses rapidly. The “free sample wire” method has the advantage of extreme simplicity. The “enclosed sample wire” technique, on the other hand, has a greater potential for control and adaption. It might be developed, by using a heated cell, to a static vapor method.
Some sensitivities and detection limits are given (Fig. 26). Compared with flame absorption, they are improved by factors of 10² to 10⁴. Analyses in the parts per trillion range are feasible.