Other Uses of Complexes

There are a number of other useful reagents for complexoraetric titrations. A notable example is ethyleneglycol bis(jS-aminoethyl ether)-N,N,N, N -tetraacetic acid (EGTA). This is an ether analog of EDTA that will selectively titrate calcium in the presence of magnesium  

EGTA allows the titration of calcium in the presence of magnesium. 

With the exception of the alkah metals, nearly every metal can be determined with high precision and accuracy by chelometric titration. These methods are much more rapid and convp ient than gravimetric procedures and have largely replaced them, except in those few instances when greater accuracy may be offered and required. 

Complexometric titrations in the clinical laboratory are limited to those substances that occur in fairly high concentrations since volumetric methods are generally not too sensitive. The most important complexometric titration is the determination of calcium in blood (see Ref. 8). Chelating agents such as. EDTA are used in the treatment of heavy-metal poisoning, for example, when children ingest chipped paint that contains lead. The calcium chelate (as Na2CaY) is administered to prevent complexation and removal of calcium in the bones. Heavy metals such as lead form more stable EDTA chelates than calcium does and will displace the calcium from the EDTA. The chelated lead is then excreted via the kidneys. 

A table of formation constants of some EDTA chelates appears in Appendix C. 

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