In a recent white paper, Restek corporation identified a simple methodology for the simple comparison of e-cigarette liquids using GC-MS and GC-FID.
E-cigarettes have been a fairly recent phenomenon. An alternative to smoking tobacco, e-cigarettes work by vaporizing a liquid which is then inhaled by the user. Despite only being available to the market for a few years, e-cigarettes are thought to be safer and less harmful to consumers when compared with smoking tobacco.
As a regulated market the production of e-cigarettes comes with the normal legal requirements to ensure products are safe for human consumption which is where Restek's research will be of great use for quality control for e-liquid producers. One of the key attractions of E-liquids is the variety of flavors users can select compared with tobacco, which has led to increased research and development for creating flavors ranging from apple pie to grape soda.
A typical e-cigarette will contain humectants (propylene glycol [1,2-propanediol] and/or glycerin), flavorants, and nicotine. Although there have been a small number of studies analysing volatile organic compounds (VOCs) and semi-volatile organic compounds (SVOCs) in e-cig liquids, these have often required very specialized techniques. Using Restek's method, any laboratory will be able to analyse e-cig liquid using GC-FID and GC-MS with thermal desorption (TD).
The study tested four of the major selling e-cigarette brands for nicotine content, impurities in the solution and impurities in the vapor. A GC-FID using hydrogen carrier gas was used to test for nicotine levels in line with the National Institute of Standards and Technology (NIST) traceable nicotine standard. Analysed results were compared with stated nicotine content on the packaging.
Impurities in the solution were tested for using GC-MS whilst impurities in the vapor were tested for using TD coupled with a GC-MS.
The results of nicotine analysis showed that all vendors stated a lower nicotine concentration on their packaging, compared with concentrations found in GC-FID analysis. These differences from detected nicotine compared with stated nicotine ranged from 0.6mg/mL to 5.7mg/mL depending on the manufacturer.
GC-FID analysis also showed that ethanol was present in the liquids from all four e-cigarette brands, an ingredient not listed by any of the vendors and shown not have been introduced to the sample in the lab by running control samples.
Impurity analysis of the solutions also identified 64 compounds when analyzing one of the e-cigarette brands. Many of these were confirmed to be the various components of e-cig flavors but 36 could not be identified and therefore there is no information is available regarding the nature or these compounds.
The analysis of the vapor found 18 compounds in addition to the 64 found in the liquid. Of these 18 additional compounds were formaldehyde, acetaldehyde, acrolein, and xylenes, as well as several siloxanes. The presence of formaldehyde, acetaldehyde, and acrolein is significant because these compounds are toxic to the human body.
The reason these compounds are present in the vapor and not the liquid was that they are likely generated via the process of vaporizing the liquid since the pyrolysis of glycerine is known to produce all three compounds.
It is evident from this research that whilst several studies have shown that e-cigarettes are a safer alternative to cigarettes, the components of e-cigarettes do contain some harmful compounds and the effects of long-term use of these substances on the human body not yet fully understood.
This study demonstrates the use of hydrogen carrier gas being used as an alternative to helium carrier gas for GC-FID analysis. Although Helium has been used as the carrier gas of choice for a number of years, because of the rising cost, inconsistent & unreliable supply many labs are now looking to change to alternative carrier gases such as Hydrogen or Nitrogen.
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Sources:
Analysis of Nicotine and Impurities in Electronic Cigarette Solutions and Vapor By Jason S. Herrington, Colton Myers, and Amanda Rigdon