Chromatography Forum

Hi!
I am testing Acid number in Avalure AC 315, using Phenolphthalein as an indicator and 0.10N NaOH as titrant..it is giving me the results out of spec, towards lower end. i talked to the vendor and they used auto titrator with electrode without any indicator. My question is can i use pH electrode to get the end point?, rather than Phenolphthalein. Only problem is I dissolved the Avalure polymer in 49:1 (acetone:H2O), so any recommendation for organic solvent electrode
which would be appropriate for the organic solvent matrix. please let me know. Thanks

The short answer is yes; there are plenty of electrodes that will give you some sort of reading in an organic solvent matrix.

The auto-titrator method, without the indicator, is superior and removes human error. If you can, you will want to graph the voltage through the probe as you titrate. The first derivative of this will give you maxima at inflection points. One of which will be your end point. Many auto-titrators will perform all of these functions for you, they cost some money, but are extremely versatile.

If you can't perform this test with an auto-titrator look at the different parts of the titration. Double check the normality of your titrant and make sure you are not over titrating.

Thanks Hysol for the reply and good information
i will find out how much auto-titrator cost!

Do I understand corectly - You get out of specification pH when making titration in an organic solvent solution? Does the vendor use the same solvent?

Because generally correct procedure is to measure pH in aqueous solutions as value in organic solvent will be different for the same compound/concentration.

You can make claim of "out of specification" to the vendor only when they specifically prescribe in the test procedure the solvent You used.