J808,
pH is by definition an aqueous property. The pH of a nic solution takes into account the pH of pure water. I could go on, but any first-year college or AP chemistry text will explain it all...it does take some time to learn it though.
The acidities of VG and PG are not equal to that of water, but they are close. The difference of the pH of say 36 mg nic in VG and 36 mg nic in water would be in the places past the decimal. Important for my purposes, since I am trying to do this measurement very accurately, but not a big issue for a kit test. You are correct, though, the two solutions are not equal. So I generally do pH vs Vol HCl titration curves on an accurately diluted sample of the nic-liquid, and then work back to what the nic content is in the original sample. A bigger issue is using an indicator's color to gauge the equivalence point. Bromo-blue is a tough indicator to see in the first place for me (eyes not as good as when I was younger), and getting full curves is more accurate anyway. Also, the acid that is used is not generally standardized very accurately, since it is not really meant for titrations, rather its for other applications, like cleaning metals. Thus, it may say 0.12N, but it might actually be 0.11N or 0.13N, which is a big difference when titrations are being considered. My acid is 0.07051M HCl, rigorously standardized to 5 ppd.
So besides the uncertainty of titrating a straight nic-VG or nic-PG solution, the other factors I list also cut back on the precision of the kit. So you can really only say your result is about +/- 10-15% accurate with the kit. My method is accurate to 0.1 mg, in general, depending on how many titrations I do on a sample.
