I saw a post on another forum about reports being made about nicotine sold by a US pharma vendor is many times stronger than the label states. A 100mg sample is said to have tested at 245mg strength. This means any resulting e-liquid made will be over double the expected strength. This may mean that 24mg liquid you make in good faith could actually be 60mg.
This doesn’t surprise me actually, because a few months ago, I bought 60mg NIC, and ended up being 100mg NIC. Not as big as difference, but still could be dangerous. Ever since then, I stress NIC testing because there are no true regulations that can prevent NIC juice being sold at too high, or too low of levels. Even a well trusted vendor can make a mistake, they are only human. (and the batch that was wrong for me was my regular well trusted vendor, which I ordered from before, and still order from. It was only a 1 time mistake in my case)
http://www.eliquidtest.com/Instructions.aspx is testing procedures with many tips, and recommendations. It’s better to be safe, and have piece of mind knowing exactly what you are vaping.
If you have any questions about the instructions, check out the FAQ page, or if your question isn’t listed there, post it here and I’ll help you out. I’ve been regularly testing all my DIY eliquid for several months now, and consider my self a pro, lol. Also, if you have you own personal story about bad eliquid or something, I’d like to hear about it.