KINETOCHROMIC SPECTROPHOTOMETRY .2. DETERMINATION OF SULPHATE BY CATALYSIS OF ZIRCONIUM-METHYLTHYMOL BLUE REACTION

A direct spectrophotometric method is proposed for the determination of sulphate, based on its ability to catalyse the slow reaction between Methylthymol Blue and zirconium in slightly aged solution. The procedure is operated in the same way as a normal spectrophotometric method but with stricter control of timing. The interference of 100-fold excesses of 40 other ions was studied. Of these, Ce(III), Sr, Fe(III), Th, Sn(II), U(V), Mn(II), Sb(III), Se(IV), Bi(III), Te(IV), SO32-, F-, PO43-, AsO43-, S2-, tartrate, oxalate and citrate interfered. Cationic interferences may be removed by cation-exchange. The interference of equimolar ratios of arsenate, fluoride and phosphate may be removed by preliminary treatment with magnesium oxide. Sulphate may be determined in the range 0·1-2·4 ppm by the recommended procedure with a net molar absorptivity of 2·0 × 104 at 586 nm. The colour development time is 60 min. © 1969.