I have a question regarding titration of guandine acetic acid. I was trying to determine the titratable amount by dissolving the compound in acidic water (pH adjusted to 1. and titrating up till pH12 using 1N NaOH.

from the derivative plot (dpH/dv), I can only see one inflection point.

I thought guandine group can not be titrated (pKa too high), but the COOH should be. Shouldn't I see two inflection points? any ideas why I am seeing just one?  

I combined conductometric titration with potentiometric titration, still saw one turning point in the conductometric plot..

Thanks in advance

I was using 0181 g of guanidine acetic acid in 51.792g solution (pH adjusted to 1.8 to make sure COOH is protonated). It's 1.546 mmol (FW 117.11)

The only inflection point I see is around pH 4, looks like the end point of strong acid neutralization (excess HCl I added in). I couldn't see any other inflection points ( I titrated till pH 12.5)

Thanks.

I don't know exactly. But I guess you are right. The structure is similar to amino acid (guanidine at the alpha location could excert some induction effect). so the pKa should be 2-3

any idea how to titrate those low pKa acids?