Cacotheline as a specific reagent for the detection of iron(II)

Summary Cacotheline gives a blue colour with iron (II) in the p_H range 5.2 to 7.8 in the presence of a suitable complexing agent like sodium oxalate or sodium citrate. The blue colour is not stable in air. It has now been shown that if the test is carried out in a Thunberg tube with the exclusion of air, the colour is quite stable at p_H 7.4 (McIlvaine buffer). This reaction affords a sensitive test for iron (II). In a test tube reaction, the limit of identification has been found to be 11 g in about 5 ml of solution. On a spot plate, the limit of identification has been found to be 0.5 g and the dilution limit 1100,000. On special Whatman spot filter paper No. 542, the identification limit has been found to be 0.3 g and the dilution limit 1166,000. The test can also be applied to iron (III) after reduction with sodium oxalate under a Philips' Repro lamp. Reducing agents like sodium sulphite, sodium thiosulphate, sodium hypophosphite, thiourea and ascorbic acid which reduce cacotheline to a pink coloured compound, just like iron (II) (in the presence of oxalate, etc.) in an acid medium, do not give the blue colour with cacotheline in the basic p_H range; Sb^III, As^III, U^III, U^IV, Cu^I, Cr^II, Ce^III, Sn^II, V^III, Ge^II, and Ti^III also do not give the blue colour with cacotheline under the conditions where iron (II) answers the test. The colour reaction now developed appears to be quite specific for iron (II).In conclusion, two of us, V. Narayana Rao and Mrs G. Somidevamma desire to thank the Ministry of Education, Government of India for the award of Research Scholarships.See also Z. analyt. Chem. 152, 346 (1956).