Five skarn -rock samples were heated with KNO3 and with a solution of 5% KOH in KNO3 for 2 h at 450°C. The decomposed samples were cooled, dissolved in water and filtered. Iron was extracted from each residue as well as from the original samples by hot conc. HCl , and determined by atomic absorption spectroscopy. These results were compared with the known (X-ray fluorescence) total iron content of the original samples. The amount of iron extracted with HCl from the skarn samples was 3-11% lower, while that extracted after heating with KNO3 alone was 2-4% lower, than the amount present according to the X-ray fluorescence results. However, the amount of iron extracted from the samples treated with a solution of KOH in KNO3 was comparable to that determined by X-ray fluorescence.
Polarographic Determination of Total Iron Content Using a Fe2+/3+-Methylthymol Blue-NO2- System