The spectrofluorimetric determination of magnesium with NN′-bis-salicylidene-2,3-diaminobenzofuran

Abstract

NN′-Bis-salicylidene-2,3-diaminobenzofuran, SABF, has been synthesised and is proposed as a stable and inexpensive spectrofluorimetric reagent for determining magnesium in the range 0·1 to 6 µg (2 × 10^–3 to 1 × 10^–1 p.p.m.). The method is both rapid and sensitive, and has a detection limit of about 10^–3 p.p.m. in 50 per cent. aqueous methanol at an apparent pH of 10·5. The orange fluorescence (545 mµ) of the 1 : 1 complex is excited at 475 mµ and can be measured within 15 to 45 minutes of mixing the solutions. Few other ions yield a fluorescence with the reagent and those that do, or that interfere in other ways, may be tolerated in 100-fold molar proportions by simple addition of masking agents. The fluorescent magnesium-SABF complex can be extracted quantitatively into isobutyl methyl ketone without interference from 2000-fold amounts of calcium, thus providing an extremely useful method for determining magnesium in technical materials, etc. To demonstrate this, nine municipal water samples and fourteen blood plasma samples have been analysed successfully for magnesium by the proposed method in a 50 per cent. aqueous methanol medium.