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Spectrotitration of ethane-1-hydroxy-1,1-diphosphonic acid (EHDP(tm)) with thorium diaminocyclohexanetetra-acetate.

Authors
Type
Published Article
Journal
Talanta
0039-9140
Publisher
Elsevier
Publication Date
Volume
17
Issue
11
Pages
1135–1140
Identifiers
PMID: 18960842
Source
Medline

Abstract

An automatic spectrotitration procedure for EHDP has been developed. It is applicable to samples containing 50mug or more of EHDP, with a relative standard deviation of 3% if no interfering materials are present. The sensitivity can be extended down to about 5mug, but titration blanks become significant and the standard deviation increases markedly. Thorium diaminocyclohexanetetra-acetate (Th-DCTA) is used as the titrant, to give a ternary species (Th-DCTA)(2)-EHDP. The end-point in the spectrotitration is due to deprotonation of Xylenol Orange indicator when it is incorporated into a weaker ternary species after all the EHDP has reacted. Salts such as NaCl, NaClO(4), Na(2)SO(4) and NaNO(3) interfere if present at concentrations of 0.1-0.5M. The method is much more sensitive to orthophosphate, but this interference can be averted by isolating the EHDP before titration by selectively adsorbing the phosphonate on calcium hydroxyapatite.

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