I'm using APTES in anh. DMF to silanize onto SiO2 surface, so need to somehow see whether the APTES free amine is dangling off that surface after the reaction. Should I use ninhydrin, or is there a better way that I cannot remember?
I recommend to use HPLC-photometric assay. Phenyl Isothiocyanate [for HPLC Labeling] may be also recommended, which has been firstly applied by famous Late Prof. Dr. Peer Victor Edman (Sweden).
Since you are derivatizing a surface, you probably can't use the HPLC method. You could react the surface with an amine-reactive fluorophore (see Molecular Probes catalog for many examples) and a fluorescence microscope to see whether the surface is fluorescent (compared with an underivatized surface.
Hi Justin
The ninhydrin-based Kaiser test1,2 is a favorite to check polystyrene beads for the presence of primary amines during manual peptide synthesis. It is simple and quite sensitive. Ninhydrin should work well for you - if you do not mind a little purple on your fingers. I had the pleasure to meet Emil Kaiser (an excellent chemist) while working with the peptide synthesis groups at Rockefeller.
Please post back and let us know what you used and how it turned out for you.
1Kaiser, et. al., Analytical Biochemistry, 1970, Vol.34(2), pp.595-598
2Wellings, D. A.; Atherton, E. “Methods in Enzymology Volume 289: Solid-Phase Peptide Synthesis” Ed. Fields, G. B. Academic Press, San Diego, 1997, p. 54.
Update:
2% ninhydrin in DMF with a few minutes of heating worked, surface was blue if amine was present.
Thanks for all of your inputs.
picric acid will generate a yellow color in solution in the presence of amines
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