is all USP grade propylene glycol safe to vape with?

[preasence]

Went to my local pharmacy this morning to chat with the compounder about ordering in some propylene glycol.
Said she could get me 500ml from one company for $11, or 500ml from another company for $40. Neither of us could figure out what the difference between the 2 was, but she was concerned that one of them may not be suitable for internal use.
Both where USP grade.
So basically I'm wondering if there are any USP PGs that are not safe/suitable to vape with.

 

[Caridwen]

Here's a helpful post by Rolygate about this topic

http://www.e-cigarette-forum.com/fo...-like-amazing-deal-bulk-vg-2.html#post5959278

 

[markfm]

I'm too lazy to buy vg bulk, just pick it up 6 ounces at a time for $5 at rite aid or cvs. It is called glycerine usp skin protectant, found near the bandaids. Humco manufactures it, it is real usp grade, vegetable based.

For pg I went the tractor supply store route, a gallon of real pg usp grade for $20 or so.

 

[preasence]

Here's a helpful post by Rolygate about this topic
This looks like an amazing deal for Bulk VG!

I read Rolygate's post. What I got from it was:
1) only use Pharmaceutical Grade PG
2) If a deal sounds too good to be true, it probably is.
$22 a liter doesn't sound too good to be true. This USP PG would be coming from a Pharmasave's(large chain in canada) compounder, hopefully meaning it's pharmacy grade...So it's safe to use?

I'm too lazy to buy vg bulk, just pick it up 6 ounces at a time for $5 at rite aid or cvs. It is called glycerine usp skin protectant, found near the bandaids. Humco manufactures it, it is real usp grade, vegetable based.
For pg I went the tractor supply store route, a gallon of real pg usp grade for $20 or so.

I have no problems sourcing VG. I'm looking for PG, and I've found some but I'm just not 100% its safe to vape.
Not a lot off tractors/cattle/farms where I live. Closest Tractor Supply is about an hour and a half drive, and I would be a little sketched about vaping PG I bought from a Tractor Supply.


Any more info/help would be appreciated. Still not sure if I should order this up.