[jyardbird]

I need some help with an amine reactivity assay.  Presently I am testing chemical reactivity in a thiol based assay an doing a colormetric reading on a spectrophotometer to determine levels of free thiol after exposing them for a period of time to various electrophiles. 
I am hoping to branch out and change the nucleophile from the thiol to an amine assay but I am having trouble finding info.  Does anyone know of  a chemical I could add to a solution that contains a primary amine and say and aldehyde that would bind to any free amine, stopping the interaction between the amine and aldehyde, and produce some sort of coloring affect that could be read on a spec.

[proufs]

Have you tried any aqueous Cu(II) salts for complexation.  Cu(II) can be used to remove amines during organic workups and will produce a blue/purple colored solution which i think should be able to be measured by UV-Vis Spectroscopy. 

workup notes:
"Wash the organic layer several times with 10% copper sulfate (aqueous and blue). The copper-complexed amine will partition into the aqueous solution, which turns purple. Continue to wash with the copper sulfate solution until no color change is observed"

[GSK]

does this method work for removal of pyridine too?

[movies]

Yes.