Understanding E-Liquid Lab Reports
With the continuing concern regarding diacetyl in e-liquids, lab reports on the contents of e-liquids are becoming increasingly common. Here at Black Note, we’ve opted to have all of our flavors tested for diacetyl, acetyl propionyl, acetoin, acrolein, acetone and ethylene glycol (as well as the expected PG and VG), but you might be a little confused about what you’re reading if you open the lab report. And if you see another manufacturer’s lab report, how do actually interpret the results to determine whether or not it’s a juice you should stay away from? Here’s a plain-language guide so you know what you’re reading, so you can make an informed decision about which juices you’re happy to vape.
The Units: Micrograms per Milliliter, ppm and ppb
The most basic and crucial element of the reports is the way the quantities are represented. In practice, this is almost always in micrograms per milliliter or parts per million, so it’s important to know what this means.
A microgram (μg) is a millionth of a gram, or a thousandth of a milligram (mg). Metric units tend to work in this relatively simple way: 1 kilogram (kg) is 1,000 grams (g), 1 gram is 1,000 mg and 1 mg is 1,000 μg (and indeed, 1 μg is 1,000 nanograms). In the same way, one milliliter (mL) is a thousandth of a liter (L).
One crucial point that’s pretty useful in interpreting lab reports is that 1 L of water weighs 1 kg, and therefore 1 mL weighs 1 g. Although the densities of PG and VG are slightly different from that of water, it simplifies matters to consider them as being the same, without making too much of a difference.
Generally, the units you’ll see in lab reports are μg/mL (micrograms per milliliter). This is fairly simple to understand: in one milliliter of juice, it will contain the specified amount of the substance (in μg), and in 10 mL of juice it will contain 10 times the specified amount.
Sometimes, though, the results from lab reports are specified as parts per million (ppm) values, which can be interpreted quite literally: if a collection of 1 million balls contains 1 single red ball, the concentration of red balls in the collection is 1 ppm. Remembering the simple rule for the mass of a given amount of water (1 mL = 1 g) and the definition of a μg, it’s pretty easy to see that 1 μg/mL is actually equivalent to 1 ppm (in terms of mass, it’s like saying 1 μg/g). Parts per billion (ppb) isn’t really used in e-liquid reports, but it’s equivalent to 1 μg/L.
If you want to visualize how much 1 ppm actually is, there are a few good examples in a document from Virginia West University: it’s like a single car sitting in bumper-to-bumper traffic stretching from Cleveland to San Francisco, or a single second in 11 and a half days. We really are dealing with tiny amounts here, but that doesn’t mean there isn’t anything to worry about.
Limits of Detection
When you read a lab report, there’s an inherent temptation to take a “not detected” (ND) result as meaning that “it’s not there,” but this isn’t necessarily the case. Imagine if there was just one part per trillion of a specific substance in a sample: you’d need some very sensitive equipment to even tell it’s there. The “limit of detection” (or “minimum detection limit”) of a measuring apparatus is central to the interpretation of results. If you were looking for the presence of nicotine in e-liquid, but your limit of detection was 1 g per mL, any e-liquid would return a ND result, even though we know there’s nicotine in there.
Both the American E-Liquid Manufacturing Standards Association (AEMSA) and the Electronic Cigarette Trade Association of Canada (ECTA) stress this point as being crucial: if the detection limit is too high, a ND result becomes considerably less informative. The ECTA points out that some gas chromatography-mass spectrometry (GC/MS) tests have a limit of detection of 0.1 %, which is equivalent to 1,000 μg/mL or ppm, which is blatantly not good enough for many chemicals of concern like diacetyl. Getting an ND result on such a test could mean that diacetyl is present in up to 999 ppm concentrations or that it’s completely absent: there is no way to tell.
The AEMSA recommends aiming for detection limits (for diacetyl in particular) of as low as 1 μg/mL or even lower. This is crucially dependent on the amount of the specific chemical that poses a risk: obviously, your limit of detection needs to be capable of spotting the presence of a chemical in dangerous quantities. Determining what classes as risky is a different matter, of course, but the general rule is that the lower the limit of detection, the better. For example, Black Note’s testing – conducted by Enthalpy Analytical – has a limit of detection of 0.279 μg/mL for diacetyl, so an ND result means that there is less than this present, if any at all.
An Example: E-Liquid Diacetyl and Acetyl Propionyl Testing
So now we’re in a pretty good position to understand what the results of e-liquid tests actually mean for you as a consumer. The best example is diacetyl (and the similar chemical acetyl propionyl, also known as 2,3-pentanedione), because this is what much of the recent controversies center on.
The first thing we need to do is find out how much of the chemical is too much. For diacetyl (DA) and acetyl propionyl (AP), this is much easier because Dr. Konstantinos Farsalinos and colleagues made a reasonable estimate as part of his study into the presence of these chemicals in e-liquid. Based on the National Institute on Occupational Safety and Hazards’ occupational exposure limits for DA and AP – which provide average concentrations which can be inhaled for 8 hours a day, five days a week with minimal risk – and the resting breathing rate for an adult, the researchers calculated a guideline maximum daily intake of 65 μg for DA and 137 μg for AP.
It’s important to note some limitations to this approach – primarily that exposure for 40 hours a week in a workplace setting is different from continuous exposure from recreational vaping – but overall it can be used as a reasonable guide.
VaporShark has recently commissioned Enthalpy Analytical to conduct testing on their own e-liquids and others that they sell, looking at DA and AP, which gives us plenty of evidence to look at to see the likely levels of risk from each juice. If you click the link above, you’ll see that many juices return ND results for both chemicals, and following the link to a specific juice gives the full details including the limits of detection, which in these cases are 1.86 μg/mL for DA and 1.57 μg/mL for AP.
This means that any juice listed as ND could only contain less than these limits. If you were to consume 5 mL of any one of these juices over the course of a day, this means you would be taking in less than 9.3 μg of DA and 7.85 μg of AP. This is simply worked out by multiplying the amount of DA and AP (or the limits of detection, in these cases) by the amount of liquid consumed, working under the assumption that DA and AP are delivered to the vapor in similar amounts to their levels in the liquid (this was determined to be largely true, based on Dr. Farsalinos’ study). For Black Note’s tests – with a lower limit of detection at 0.279 μg/mL for DA and 0.281 μg/mL for AP – vaping 5 mL would lead to less than 1.4 μg of DA or AP consumed, well below the recommended maximum intake.
Now let’s look at a juice with reasonably high quantities of DA and AP, Vanilla Sky Tobacco by Hurricane Vapor. The testing found 25.2 μg/mL of DA and 147 μg/mL of AP in the e-liquid, which for a consumption of 5 mL of e-liquid per day would lead to 126 μg of DA and 735 μg of AP consumed per day: 94 percent more than and over 5 times more than the recommended intakes, respectively. 5 mL per day is a fairly extreme assumption, but these would both exceed recommendations for even just 3 mL of e-liquid consumed per day.
Suicide Bunny and VaporShark – Controversy and Uncertainty
Since Suicide Bunny’s Mother’s Milk was a big source of DA and AP controversy, the results of testing on this juice are also worth considering. One test was conducted by Enthalpy on behalf of Russ from Click, Bang!, and found levels of DA at 5.46 μg/mL and AP at 400 μg/mL in the juice, working out to 27.3 μg and 2,000 μg consumed if you vaped 5 mL of it. This was disputed, and the manufacturer released other results (from a different lab) suggesting that Mother’s Milk contained less than 5 ppm (remember that this is equivalent to μg/mL) of DA and 9.87 ppm of AP, putting them well within recommended exposure limits. Other tests have also been conducted, but overall we’re left with a confusing situation in which different labs give different results.
VaporShark’s testing has resulted in similar issues, with one manufacturer noting a huge discrepancy between testing it commissioned and those conducted by Enthalpy. There’s a whole rabbit hole to try to get to the bottom of here, with some claims of identical e-liquids sent to Enthalpy receiving different results, but we’re well into the realm of speculation here, and other labs haven’t yet received the same type of scrutiny.
Hopefully this post has given you some confidence in looking over and understanding results of lab testing of e-liquids, but it’s important to remember (as the Suicide Bunny saga and the recent VaporShark controversy shows) that any test is not the gospel truth. Ultimately, humans conduct every test and humans are fallible, and e-liquid testing doesn’t necessarily have the same rigor as peer-reviewed science. We’re sure that test results can be trusted, on the whole, but you should exercise some caution in taking the results of any one lab test as fact.