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the free ions from the measurement pool.
+ EDTA <—>Cd-EDTA
2+
Cd
The EDTA reacts with the cadmium ion forming a complex.
The EDTA also can react with a host of other metals. Working
at a pH between 4 and 6 optimizes the pH of the Cd-EDTA
complex, and also discourages complexing with other ions
that form stable complexes at high pH. Consult a
comprehensive Analytical Chemistry Treatise for techniques
concerning your particular interferent. The end point is
assumed to be at the inflection of the mV versus titrant
volume curve. Measurements may be automated by use of
the Hanna Titrator HI 901 or titrated manually.
Notes: .
Addition of ISA is suggested (1part/50parts sample).
Use of the an acetic acid buffer may increase the end
point break. Prepare buffer by diluting glacial acetic
acid (17.4 M) to 1M and adjust to pH 5 with KOH.
Add 1part buffer to 10 parts sample.
The EDTA titrant should be 10X more concentrated
than the expected cadmium concentration.
Competing metals will need to be identified and
removed or masked.
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