Substoichiometry in isotope dilution analysis
: automation of the process with reference to mercury

  • B.G. Cooksey

Student thesis: Doctoral ThesisDoctor of Philosophy


Substoichionetry is a radiochemical technique which
greatly improves the sensitivity of trace metal analysis
by solvent extraction procedures. The basis of the
technique is the use of a smaller amount of reagent than
the stoichiometric amount required by the metal. In
this way the same amount of metal is always extracted.
This is convenient in isotope dilution analysis because
the activity of the organic phase is then proportional
to the specific activity. There is no need to measure
the amount of metal actually extracted and a reagent can
be used at a low concentration which cannot be measured
by conventional techniques.

A method of determining mercury by substoichiometric
solvent extraction, hich has previously been described
by Ruzicka and Stary (RL), has been automated and its
limitations investigated and compared with those of the
manual method (B5).

During the course of this investigation chloride
was found to interfere by forming a ternary complex,
mercuric chloride dithizonate. The reactions and
properties of this substance have been studied and its
stability constant has been determined (B6).

Several methods of overcoming this chloride interference
have been examined. Whilst exploring one of these
methods, the addition of ethylene-diamine-tetra-acetic
acid, another ternary complex, mercuric chloride ethylene-diamine-tetra-acetate, was recognised and its stability constants have also been measured.

Two papers have been published reporting this
work (B5, B6) and a third is being prepared.
Date of Award1969
Original languageEnglish


  • substoichiometry
  • isotope dilution
  • mercury

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