Some observations on the determination of iron by atomic-absorption spectrophotometry using air-acetylene flames

Abstract

Calibration graphs for iron solutions in fuel-rich air-acetylene flames have been shown to exhibit inflections and even maxima; the response for a given standard can also depend on the age of the solution. Under these flame conditions iron(II) and iron(III) gave significantly different calibration graphs. These effects disappeared in a fuel-lean air-acetylene flame, but this resulted in a considerable loss in sensitivity.

In fuel-rich flames low levels (0.5–5 µg ml^–1) of silicon were found to enhance the iron response significantly. For a given concentration of silicon the degree of enhancement increased with increasing iron concentration. The presence of 100 µg ml^–1 of calcium was found to suppress the response slightly at the 0.5 µg ml^–1 iron(III) level whilst giving a very significant enhancement at the 5 µg ml^–1 iron(III) level. In the fuel-lean flame up to 10 µg ml^–1 of silicon or 100 µg ml^–1 of calcium had a negligible effect on iron(III).

The fact that anomalous calibration graphs, age of solution effects and inter-element effects of silicon and calcium were not observed in the presence of 2%m/V ammonium perchlorate was taken to indicate that a condensed phase effect was responsible for the observed phenomena.

This study clearly shows that for iron determinations in the absence of ammonium perchlorate, fuel-rich flame conditions that correspond to maximum iron sensitivity should not be used and fuel-lean flame conditions that result in a decreased sensitivity are recommended.