I planned to modified a polydopamine coating with other catecholamines in order to increase the primary amino groups, for many original primary amino groups become secondary ones when being cyclized. Apparently, I cannot directly gauge the amount of nitrogen because I have to exclude the secondary amino groups to prove that I have successfully modified the coating.
So how can I do it? Can MALDI-TOF-MS possibly do this job?
You can use the UV/VIs combined with the ninhydrin indicator. The greater the intensity of the blue color, the greater the amount of amino groups.
Rafael Da Silva Fernandes Thank you sir! Yeah I've thought about this method and I also considered formaldehyde titration. I wonder if there is any other way that could be more accurate, considering that the greater amount of amino groups in the sample, the deeper colour the sample will become and deep colours may be difficult to analyse and cause deviations. Besides I believe that ninhydrin can react with secondary amino as well generating a yellow substance. Does this yellow substance possibly affect the characterization of primary amino groups?
You could use the fluorescamine test, it reacts with the primary amino groups to form fluorescent pyrrolinone moieties. Simply measure the fluorescence of your sample and extrapolate in a calibration curve
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