ISSN 1017-2548(Print)
ISSN 2234-8530(Online)
Volume 17, Number 4
JKCSEZ 17(4)
August 20, 1973 

Complex formation of magnesium-Eriochrome Black T at constant ionic strength and hydrogen ion concentration have been studied spectrophotometrically in acetonitrile solution. The measured pH values were calibrated with standard buffer solutions by using a glass electrode Ag/0.1M AgNO3 reference electrode couple. The results are as follows; Eglass= 716 + 59.1 log AH+(in mv. vs. Ag reference electrode for picric acid -1.0×10-3M tetramethylammonium picrate buffer), and Eglass= 1193 + 59.1 log AH+(in mv. vs. Ag reference electrode for 1,3-diphenylguanidine 3.0×10-3M 1,3-diphenylguanidine perchlorate buffer). The acid dissociation exponent of ligand, pKH2EBT- was found to be 9.1. The conditional formation constants of Mg-EBT-complex by log-ratio method were 3.97 (when m = 2) and 5.02 (when m = 1) as log Kn, respectively, for the reaction of HmEBT(3-m)- + Mg2+ = MgEBT- + mH+. The present study showed that Mg-EBT- has the composition of 1:1 which agrees with the result of Schwarzenbach et al. in aqueous solution.