Dear Sir. Concerning your issue about the measurement of the pH of DTPA. The DTPA salt is hygroscopic and should be dried before use. The solution of DTPA can be prepared by taken 125 mg of DTPA with an accuracy of 0.1 mg in a 1000 ml volumetric flask, dissolve in a few millilitres of sodium hydroxide and fill up to the mark with water. I think the following below links and the attached file may help you in your analysis:

http://cool.conservation-us.org/byorg/abbey/an/an09/an09-5/an09-505.html

https://pharmacyce.unm.edu/nuclear_program/freelessonfiles/Vol16Lesson5.pdf

https://www.physics.iupui.edu/Starman/Professional/Reprints/Zaplatin_Baker_Kleinhans_ESR_1996.pdf

Thanks

Thank you sir for your response , but I want to know the raw pH value without adding any other chemicals. DTPA suspension in water, NaOH may change its pH value.

Hello, in USP, to measure the pH of starch, which can not solve in water, USP pH < 791 >: Prepare a slurry by weighing 20.0 g +- 100 mg of Topical Starch, transferring to a suitable nonmetallic container, and adding 100 mL of water. Agitate continuously at a moderate rate for 5 minutes, then stop agitation, and immediately determine the pH to the nearest 0.1 unit: the pH, determined potentiometrically, is between 4.5 and 7.0.  

so i think if you measure the pH of DTPA suspension in water, with controlling the conditions, and can search more information