Sulphonated alizarin fluorine blue. Part II. Fundamental solution chemistry and an improved isolation procedure
Abstract
Sulphonated alizarin fluorine blue {3-[N N-di(carboxymethyl)aminomethyl]-1,2-dihydroxyanthraquinone-5-sulphonic acid}, or its monopotassium salt, shows promise as a general reagent for metals and as a positive absorptiometric reagent for fluoride. An improved purification procedure for the reagent is described. The acid-dissociation constants are pK1= 0·5; pK2= 1·4; pK3= 2·5; pK4= 5·8; pK5= 10·0; and pK6= 12·3. Detailed pH-absorption spectrum graphs and pH-absorbance graphs are given, together with the distribution diagram and the likely ionisation scheme. The following solubilities at 20 °C have been deduced: H5A, 4 × 10–5M; K+.H4A–, 5·6 × 10–3M; and K2+.H3A2–, >4·4 × 10–2M.