In the last e-cigarette blog we (Amanda, Colton, and me) showed you a quick proof of concept for analyzing the major constituents of e-juice. Working from that starting point, we realized that some labs may not have access to a GC-MS and/or some may only be interested in a very quick screening method for the nicotine content in e-juice. So… that is exactly what we’re showing you today.
The table below contains all the specifics of interest for a rapid GC-FID screening method for nicotine in e-juice.
We continue to use our thick film volatiles column, because the ultimate goal with e-smokes is to see what is in the vapor. Also, it is already doing an excellent job on the current application. So we simply bumped up our starting temp to 100 and now we have a 5 minute run (see below).
Okay… so there may be a little bit more. As we mentioned last time, we purchased some raw e-juice and analyzed it as is (i.e., straight from the refill bottle). Well since the last blog we have learned that the e-juice is extremely viscous. If you plan to analyze the e-juice raw (i.e., without any dilutions) you will have to set up your injector appropriately (see below). We suggest you include at least one sample wash; lower the sample wash speed down to ~30 µL/min; and you may also want to add in a viscosity delay. Close observation of your autosampler syringe coupled with a little experimentation will get you to where you need.
Alternatively, you could just simply dilute your e-juice, which is ultimately what we suggest. If you want to have quantitative nicotine results, clearly you will need to calibrate your instrument. So when you use our nicotine standard at 1,000 µg/mL you will realize that most of e-juice nicotine concentrations are well above this. So… a nice 100 fold dilution with methylene chloride (yes, methylene chloride and not methanol if you want to look at ethanol) will kill the following two birds with one stone: 1. you no longer have viscosity issues. 2. your concentrations fall nicely into your calibration curve.
Speaking of which… the aforementioned method calibrates fairly well [i.e., the correlation coefficient (r) (not the coefficient of determination (r²)) = 0.99562] from 1.6 x 10-2 to 1.0 mg/mL (see below). FYI – most e-juice nicotine concentrations are ~10 to 20 mg/mL for a 1.8% nicotine solution. Remember… we diluted by 100 fold, so we typically injected 0.1 to 0.2 mg/mL. Well within the aforementioned calibration curve.