DETERMINATION OF TRACE AMOUNTS OF GALLIUM, INDIUM AND THALLIUM BY SUCCESSIVE TITRATIONS USING SEMI-XYLENOL ORANGE WITH SPECTROPHOTOMETRIC AND OR VISUAL END-POINT INDICATION

The precision and accuracy attainable in successive titrations of Ga3+, In3+ and Tl3+ with a 0.001 mol dm-3 solution of disodium ethylenediaminetetraacetate (Na2EDTA) using Semi-xylenol Orange (SXO) as a metallochromic indicator with spectrophotometric and/or visual end-point indication were studied. Indium(III) was initially titrated directly at pH 5.4-5.8 (490 nm) by using hexamethylenetetramine (hexamine) buffer in the presence of ascorbic acid to reduce Tl3+ to Tl+. At the indium end-point, an excess of Na2EDTA was added, and Ga3+ was determined by back-titration with a standard PbCl2 Solution. Gallium(III), In3+ and Tl3+ in another aliquot were determined by indirect titration of an excess of Na2EDTA with a standard PbCl2 solution at pH 5.4-5.8 (490 nm). The interference of various anions, cations and organic acids in the determination of Ga3+, In3+ and Tl3+ WaS StUdied. A comparison of the indicators SXO and Xylenol Orange for successive titrations of the metal ions studied was carried out.