E-liquid Testing Results


Recent developments in the understanding of e-liquid safety and the effect of some of the flavour components have led to increased scrutiny across the industry with regards three key compounds. While these three compounds are used safely in food, special consideration must be given to inhalation use because the lungs are not equipped with the same level of defence mechanisms compared to the stomach i.e. when something is swallowed. This blog discusses these compounds of interest, why they need to be monitored and how Liberty Flights is ensuring the quality and safety of our e-liquids.

What is Diacetyl (DA)?

Diacetyl (or butane-2,3-dione) is an organic compound with the structure shown below:


It is classified as an alpha diketone (two C=O groups, side-by-side, ringed in red) and has an intense, buttery flavour. This means that it is often added to food as a flavouring agent but it can also occur naturally in alcoholic beverages.

What is Acetyl Propionyl (AP)?

Acetyl propionyl (or 2,3-pentanedione) is another alpha diketone with the structure illustrated below:


AP also has a buttery taste and can be found in food flavourings.

What is Acetoin?

Acetoin (or 3-hydroxybutanone), is a ketone (ringed in red), not a diketone like DA and AP, and has the structure shown below:


Acetoin is described as having a pleasant buttery odour, making it a popular food flavouring. It is also a chemical intermediate in the production of DA.

Why shouldn’t they be present in e-liquids?

During the use of DA as a flavouring for butter popcorn in the US, it was discovered that workers exposed to the flavouring during manufacture were at risk of Bronchiolitis obliterans (BO). BO is a rare and life-threatening form of non-reversible obstructive lung disease in which the bronchioles (small airway branches) are compressed and narrowed by fibrosis (scar tissue) and/or inflammation. After investigation, it was concluded that DA contributed to the damage caused and there is good data to support the presumption that both DA and AP are dangerous if inhaled (see links below). Evidence suggests the respiratory damage is linked specifically to the functional group of these molecules (an alpha diketone).

(1)    http://www.cdc.gov/niosh/updates/upd-08-15-11.html

(2)    http://tpx.sagepub.com/content/36/2/330.short

(3)    http://tpx.sagepub.com/content/40/3/448.short

What is most concerning is that the maximum exposure limits for DA and AP are very low and it is vital that these compounds are tested for, at the lowest possible level, in any inhalation product. The recommended exposure limit (REL) for DA is 5 parts per billion (ppb) as an eight-hour, time-weighted average, (TWA) during a 40-hour work week. For AP the REL is 9.3 ppb(1).

This data has been applied to e-liquids by registered toxicologists (BIBRA Toxicology and Consulting) contracted by ECITA (Electronic Cigarette Industry Trade Association), who have set limits for DA and AP to 20 µg/ml in e-liquids, based on a daily consumption of no more than 3 ml of e-liquid per day. The possible inclusion of DA and AP, at any level, in some sweet tasting e-liquids is therefore a concern to the industry in general. According to the British Standards Institution (BSI) PAS 54115:2015 (Vaping products, including electronic cigarettes, e-liquids, e-shisha and directly-related products – Manufacture, importation, testing and labelling guide) these compounds are not permitted in the production of e-liquids.

Although not a diketone, there is conflicting evidence about the effect of acetoin on the body when inhaled. What is known is that it is a respiratory irritant and combined with the fact that it is an intermediate in the formation of DA, it has become a compound of concern. Bibra have quoted a safe level of 8400 µg/ml and Liberty Flights Ltd has chosen to test for and monitor acetoin levels as more data continues to become available.

Liberty Flights has taken the step of having our e-liquids tested at an independent, GMP laboratory to confirm that the level, if any, of DA, AP and acetoin are within acceptable, safe limits for inhalation.

How and where is the testing performed?

In order to get the highest quality, reputable data, Liberty Flights approached a well-known independent, GMP (Good Manufacturing Practice) laboratory and undertook extensive method development to create a method which had the highest possible level of sensitivity, despite the often complex mix of flavourings.

It was important to Liberty Flights to use an accredited laboratory that would perform the testing to the highest standard so selecting one with GMP approval was vital. GMP outlines the standard required in order to conform to legislation covering pharmaceutical manufacture and testing. As a result, standards are very high and ensure reputable, repeatable data is obtained.

Using an independent laboratory was also important to Liberty Flights, as we wanted the results to be unbiased, giving our customers confidence that the results were verified independently without interference from anyone invested in the outcome.

The method for detecting and quantifying DA, AP and acetoin uses High Performance Liquid Chromatography (HPLC). This approach separates compounds of interest from each other in the e-liquid. In HPLC, the sample is passed through a column (usually containing silica based packing), with a flowing solvent mixture through the system. Based on their structure, the individual components in the e-liquid sample have unique affinities for the packing material (i.e. silica) and the solvent mixture, and retain on the column for different periods of time relative to that affinity, before being eluted. This allows the different components to be detected as discreet peaks at different times by the detector.


Example of a HPLC chromatogram


The concentration can then be calculated based on the intensity of the response to that compound in the detector (area under peak). This is a widely used analytical technique and the method development carried out by the laboratory ensured the limit of detection (LOD) and limit of quantification (LOQ) for the method was as low as possible whilst maintaining precision and specificity.

XO e-liquid Results


The certificates for the first 27 liquids tested can be found where you see the certificate symbol next to any flavour on the product pages. Due to the number of liquids available, this process is ongoing and as more results become available they will be published on the relevant product pages of our website.

For reference, 1 µg/ml equals 1 ppm and therefore, the safe limit of 20 µg/ml referenced previously equals 20 ppm for DA and AP and 8400 µg/ml equals 8400 ppm for Acetoin.

The limits of detection for the methods used to conduct this testing are 2 ppm. It can therefore be said that any e-liquids showing a result of ‘none detected’ (ND) have levels below 2 ppm and are therefore well within safe limits.

Liberty Flights is pleased that the results reflect the thorough approach taken to e-liquid quality.

Guest liquids

At Liberty Flights all of our guest e-liquid manufacturers are required to supply the appropriate certification on DA, AP and acetoin levels to ensure we only sell the best quality products. Please contact the manufacturer directly for more information.

A Final Note

Liberty Flights will continue to invest resources into scientific development to ensure that we produce e-liquid that is of the highest quality and is as safe as it can possibly be. If you have any questions about this blog, or anything else about Liberty Flights products, please feel free to get in touch via our customer service team or leave your comments below and we will do our very best to get back to you as soon as possible.


Lucy Robins

Chief Scientific Officer

How do e-cigarettes satisfy my nicotine craving vs. traditional cigarettes?

liberty-flights-cost-saving-blog Accurately estimating the cost and other benefits from switching to e-cigarettes can be challenging and requires a good understanding of the vast differences between e-cigarettes and traditional cigarettes. Therefore, the objective of this blog is to discuss these key differences to help you more accurately predict the cost savings and other benefits from initially switching to e-cigarettes and throughout each stage of your vaping journey.

Nicotine Absorption

The amount of nicotine present in your blood after consuming nicotine is referred to as nicotine absorption.1-3 Given the variety of brands and sizes, a single traditional cigarette or alternative nicotine-containing products can significantly vary in nicotine content.4 In addition, nicotine consumers are not only interested in the amount of nicotine absorbed but also how fast you feel its effects. The manner of which you take in nicotine (e.g. smoking, nicotine gum) will significantly influence this rate.5 Cigarettes have been around since the early 1800s and consequently they are thoroughly studied and well understood. In contrast, there are only a limited amount of investigations on nicotine absorption from e-cigarettes to date and even fewer studies that compare the difference in absorption between e-cigarettes and cigarettes.5-10

Hajak et al. evaluated the nicotine absorption from 6 individuals using a 1st generation device that contained 2.4% (w/v) nicotine. The authors concluded that the absorption from e-cigarettes was faster than nicotine replacement gum and nasal spray but slower than conventional cigarettes and state that in order to compete with cigarettes, the nicotine dose should increase. However, this does not mean that you should start off vaping >2.4% (w/v) because nicotine absorption will also depend on your experience with vaping and selected device.5  

Vaping experience

The authors from the study described above evaluated the nicotine absorption following a first time user experience and after 1 month of vaping. Results showed a 24% increase in nicotine concentration and a 79% increase in overall nicotine intake after 4 weeks of vaping experience.This increase over time can be attributed to the users “adjusting” to the puff differences between smoking and vaping.6

A study evaluating vaping patterns, observed that experienced vapers take a longer puff compared to cigarette smokers vaping for the first time.6 This was explained by the fact that smokers are used to inhaling an already burning cigarette, while vapers produce an aerosol only at the time of activation. Consequently, vapers will compensate for this by taking longer puffs. Another important consideration is the difference in puff strength. Smokers will draw harder puffs in order to produce more smoke but this has no effect on aerosol production when vaping.6 In a follow-up study, the authors took these findings a step further and evaluated differences in nicotine absorption between experienced vapers and first-time users (Figure 1).7


Figure 1. Average nicotine plasma concentration vs. time profiles for n=24 experienced vapers and n=23 first-time vapers (cigarette smokers).7

Figure 1 shows the average nicotine plasma concentration vs. time profiles for experienced and first-time study participants using the same device and e-liquid containing 1.8% (w/v) nicotine. While no statistical differences were observed at the start of the experiment (8 hours of nicotine abstinence), the data illustrate a significant difference in nicotine absorption for all following time points. Unfortunately, the variability within each group is not shown in Figure 1. Overall, the results indicate that first-time users are unable to obtain similar nicotine levels as experienced vapors even when using the same device.

Device Performance

Using a 1.8 % (w/v) e-liquid, Farsalinos et al. compared the nicotine absorption from a 1st and 2rd generation device with experienced e-cigarette users. The authors report a 35–72% higher nicotine concentration when using the 2rd generation compared to the 1st generation device.8  In a more recent study by St. Helen et al., the authors measured the nicotine plasma concentration of experienced vapers using their device and e-liquid of choice.9 The authors report that average nicotine concentrations from e-cigarettes were lower than average levels from cigarettes, but within the range of many smokers. The authors also report variability between vapers, which is not unexpected but the range of device types used in this study adds to the complexity of results interpretation. Figure 2 shows the results from 3 individuals and Table 1 lists the nicotine concentration vaped and device generation used. As shown in Figure 2, participant 7 obtained the highest nicotine blood concentration up to 15 min followed by a similar concentration to participant 2 after 30 min. As listed in Table 1, participant 7 selected a 2nd generation device but vaped the lowest concentration e-liquid. Participant 1 (also used a 2nd generation device) resulted in the lowest concentration of the three but vaped the highest e-liquid concentration of 2.4% (w/v). These observations from Farsalinos et al., clearly illustrate the influence of the device type (and not only generation) on nicotine delivery efficiency.8,9


Figure 2. Nicotine plasma concentration vs. time profiles of 3 participants.


Table 1. Participants’ usual e-cigarette and e-liquid used in the study. Adapted from Tables 1 and 2 of reference 9.


E-cigarette popularity is attributed to their ability to satisfy nicotine cravings more efficiently than other nicotine replacement therapies.5,9 Moreover, they also mimic the behavioral addiction more so than any other nicotine replacement product. The wide variety of devices is an attraction for experienced e-cigarette users but can be intimidating to a novice. If you are completely new to vaping, it is extremely important to take the time to learn about their various features and how to properly care for them. Liberty Flights recommends using a 2nd generation device to begin your vaping journey but encourages you to adapt your puffing style to maximise the nicotine intake from e-cigarettes. Initially, you may need to take more puffs throughout the day to satisfy the nicotine craving you get from cigarettes. It’s important to keep in mind that smoking a cigarette has a beginning and end whereas you will most likely vape throughout the day. Another advantage with vaping is that you can do it in most areas where smoking is prohibited. As you adapt your puffing style and learn more about the hardware, you can start customising to suit your preferences. Examples of these include decreasing your e-liquid nicotine concentration, selecting a more sophisticated device and/or experiment with different flavours and/or base ratios.

How much money will I save by switching to e-cigarettes?

We’ll answer this based on the assumptions that the nicotine absorption from an EVOD2 is similar to smoking a cigarette and that the puffing styles do not influence nicotine absorption:


Cigarettes: 1 pack of standard cigarettes = £8.50. If you smoke 1 pack per day then that comes out to £3102.50 per year. The cost of lighters, matches and/or ashtrays is assumed to be ~ £30/year.

Total cost = £3132.50/year

Taste Kit: Includes EVOD2 clearomizer, eGo 900 mA/h battery, charger, and 10 ml 1.8% (w/v) XO e-liquid = £24.99 for initial set-up costs. We estimate the running costs as follows:


The average vaper consumes approximately 3 ml/day = 1095 ml of e-liquid/year. A 10 ml Liberty Flights XO bottle = £4.85, therefore you will purchase ~ 108 bottles/year (in addition to the 10 ml included in the starter kit). £4.85 * 108 bottles = £523.80/year

Atomisers running costs:

Atomiser last on average 2.5 weeks, therefore you will need to purchase ~ 20 atomisers/year. A 10 pack of Kanger Dual Heads = £19.98 * 2 = £39.96.

Total e-cigarette cost = £588.75/year

Total savings of £2,543.75/year


Monica Vialpando

Chief Scientific Officer



1 Kalowski et al. Filter ventilation and nicotine content of tobacco in cigarettes form Canada, the United Kingdom, and the United States. (1998) Tob Control 7:369-3751998)

2 Benowitz and Jacob (1984) Daily intake of nicotine during cigarette smoking. Clin Pharmacol Ther 35:499-504.

3 Ling and Parry (1949) The amount of nicotine absorbed in smoking. Brit J Pharmacol 4:313-314.

4 Digard et al. (2012) Determination of nicotine absorption from multiple tobacco products and nicotine gum. Nic Tob Res doi: 10.1093/ntr/nts123

5 Hajak et al. (2015) Nicotine intake from electronic cigarettes on initial use and after 4 weks of regular use. Nic Tob Res 17:175-179.

6 Farsalinos et al. (2013) Evaluation of electronic cigarette use (vaping) topography and estimation of liquid consumption: implications for research protocol standards definition and for public health authorities’ regulation. Int J Environ Res Public Health 10:2500-2514.

7 Farsalinos et al. (2015) Nicotine absorption from electronic cigarette use: comparison between experienced consumers (vapers) and naÏve users (smokers). Sci Rep 17:11269

8 Farsalinos et al. (2014) Nicotine absorption from electronic cigarette use: comparison between first and new-generation devices. Nature Sci Reports doi: 10.1038/srep0413

9 St. Helen et al. (2015) Nicotine delivery, retention, and pharmacokinetics from various electronic cigarettes. Addiction doi: 10.1111/add.13183

10 Dawkins and Corcoran (2014) Acute electronic cigarette use: nicotine delivery and subjective effects in regular users. Psychopharmacology 231:401-407