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.