Colorimetric method for the determination of iron in pyrethrum extracts

Abstract

It has been shown that pyrethrum extract is contaminated with iron during processing and that it is necessary to destroy the organic matter before determining the metal. Wet oxidation has been carried out with a mixture of sulphuric and nitric acids, but this treatment may lead to the precipitation of an iron complex. It was found that addition of potassium sulphate prior to oxidation prevented the precipitation of this complex. The iron can be determined spectrophotometrically at 480 nm by use of its thiocyanate complex. Nitrous acid residues from the oxidation must be removed by boiling with water and nitric acid added to oxidise iron(II) ions. The resultant method for determining microgram amounts of iron is both rapid and precise with small weights of extract, but when weights greater than 0·1 g are digested loss of sulphuric acid by evaporation causes small errors.