Question about TBA/acetic acid titration for PIC

[ChromatographyKid1]

We have some samples in our lab that we need to analyze via LC/MS and have figured TBA to be the best ion pair reagent for the separation. Literature values show about 2.5mmol/L TBA titrated to pH 8 with acetic acid. I made up some mobile phase (20%MeOH/80%H2O), calculated 2.5mmol to be ~0.596mL, and used a micropipette to deliver that. I started doing the titration, after a very small amount of acid was added (about 0.2mL of 1M acetic acid) the pH dropped from over 9 to about 6, then as it equilibrated, slowly went back up above 9 over a period of about 20 minutes. It seems like this titration would take a long time to do accurately every time new mobile phase is made, so is it okay to titrate pure TBA with an acetic acid solution to pH 8 then add that to mobile phases as the PIC, instead of doing the titration after the TBA has been added? I was thinking it might act like a buffer in that the absolute concentrations don't matter as long as the ratio is right, but I wasn't positive if the pH would change upon adding to mobile phase. Does anyone have experience with this PIC, and if so, how did you go about the titration? Thanks in advance

[ChromatographyKid1]

May have solved my problem. I just ended up doing the titration in methanol because TBA is more soluble in methanol, the pH acted more as it should. After adjusting to pH 8 in MeOH (ended up being an equimolar amount of HOAc added) I diluted to volume and adjusted the matrix to form the right mobile phase conc.