[gabroxy]

I was assigned to find several methods to increase the EDTA selectivity and I only found two :the pH & the Masking agents plz help
Thx in advance

[Borek]

I doubt you will find much more. Concentrate on examples - what ions can be masked and how.

[Dedalus]

Check out Meites' Handbook of Analytical Chemistry. There is a table of EDTA titrations that contains every imaginable masking strategy.

[kevins]

How about,

Demasking agents
Cyanide complexs
Solvent extraction
Anions
Kinetic masking
chosen of indicator..

[Borek]

Demasking agents
Cyanide complexs

I will put these into 'masking' category.

Solvent extraction

That's a sample preparation, not EDTA selectivity?

Anions

Could you elaborate?

Kinetic masking

That's a new one!

chosen of indicator..

That's a new one too, but I wonder if it is changing EDTA selectivity - it rather helps to determine intermediate ending point. Or am I wrong?

[gabroxy]

Thx guys
I think i need more research to do....

[kevins]

Thanks Borek comment.

1. Yes,I agree the demasking agents and cyanide complexs are the 'masking' category.

2. I think increase the selectivity is same as increase the EDTA react to the target metal. Therefore by controlling the pH, use of masking agents, solvent extraction ...are the methods or procedures for such purpose.

3.Some of anion such as phosphate in the sample will interfere the selectivity of EDTA. So this must remove before analysis.

4.Under some conditon, the metal does not effectively entre into the complexation reaction. For example determination of Cr and Fe in steel sample solution. Under cool condition,the EDTA react with Fe first and then heat the solution, the EDTA react with Cr.

5.Different indicator have different reaction rate.

Please correct me if I get wrong. Thanks.

[Borek]

3.Some of anion such as phosphate in the sample will interfere the selectivity of EDTA. So this must remove before analysis.

As far as I remember such interference is nothing else than complexation - so I will classify it as masking/demasking thing.