Arsenazo 111 as a metallochromic indicator for the direct DPTA titration of lanthanons in alumino-silicate zeolites
✍ Scribed by William W. Marsh Jr.; George Myers Jr.
- Publisher
- Elsevier Science
- Year
- 1968
- Tongue
- English
- Weight
- 352 KB
- Volume
- 43
- Category
- Article
- ISSN
- 0003-2670
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✦ Synopsis
Aroenazo III as a metallochromic indicator for the direct DTPA titration of lanthanons in alumina-silicate zeolites* Arsenazo III may be used for the spectrophotometric determination of many metals including the lanthanons 1. Recent extensive studies of the reagent+5 indicate diverse analytical applications for it, but arsenazo III has served previously as a metallochromic indicator only in an EDTA titration of micro amounts of sc,andium-(III)O. The present paper describes the direct titration of total lanthanons in aluminosilicate zeolitcs, such #as molecular sieve catalysts, with diethylenetriaminepentaacctic acid. When used in the system described below, arsenazo III offers advantages over the commonly used indicators xylenol orange, methylthymol blue, or arsenazo I. Sulfosalicylic acid masks aluminum(II1) andiron(II1) whichdonothavetoberemoved. Large a.mounts of sulfate can be tolerated, and the accuracy and precision are superior to those for the classical oxalate precipitation gravimetric method. The rapidity of the titration and the superiority of arsem2izo III under various conditions suggest broad applicability for the method. Reagents Prepare 0.025 M DTPA (diethylenetriaminepentaacetic acid) by dissolving 9.83 g of the reagent in 75 ml of hot I M sodium hydroxide and diluting to I 1. Standardize the DTPA against a solution containing 5 mg of lanthanon per ml prepared from a lanthanon sesquioxide (LnzOa) at least 99.9% pure. Ignite the sesquioxidc at goo"C for 30 min to remove adsorbed water and carbon dioxide before dissolution in a mineral acid. Prepare an aqueous 0.5% (w/v) solution of arsenazo III from 2.2'~[(x,8dihydroxy-3,6-disulfo-z,7-naphthylene)bis(azo)Jdibenzenearsonic acid, disodium salt (J. T. Baker Chemical Company).