Nicotine identification

The use of  electronic nicotine delivery systems (ENDS) spreads rapidly, being less harmful than the use of conventional cigarettes. Cigarette smoke is reported to contain more than 6000 chemical constituents, which are formed during different chemical reactions such as distillation, pyrolysis, and combustion. Moreover, it has widely acknowledged the presence of more than 100 harmful and potentially harmful constituents (HPHC) in tobacco and cigarette smoke. In return, ENDS are designed to avoid such a number of potentially harmful components by nicotine identification.

Fig 1. Ball and stick mode of a nicotine molecule

Obviously, the emergence of new systems entailed numerous researches to understand compositions of aerosol and substances used to generate it. However, there are some regulations of the concentration of acceptable components (including nicotine) that are in substance or formed as a result of chemical reactions. Nowadays, there are some of them concerning nicotine: nicotine-containing liquids must not contain more than 20 mg/ml nicotine. Therefore, the demand for nicotine identification, calculation of its concentration or percentage in electronic liquids and aerosols is growing. In this article, the methods for the identification of nicotine and other constituents in e-liquid and in the aerosol are described.

Nicotine is a tobacco alkaloid (C10H14N2) with the ball-and-stick model as represented in Fig 1. Nicotine is a nitrogen-containing organic substance. Nitrogen, which is part of the nicotine molecule, gives this alkaloid the properties of the base. During various reactions, nicotine can form other compounds that also affect the level of harmfulness of the product consumed by the user during smoking.

Unfortunately, there are not many simple methodologies that can accurately identify various compounds in nicotine-containing products. However, there are precise methods that can be used to determine:

  1. The presence of nicotine in e-liquid (chemical method, surface-enhanced Raman scattering (SERS), gas/liquid chromatography (GC/LC) + mass spectrometry (MS).
  2. The concentration of nicotine or other components in the e-liquid or in aerosol (gas/liquid chromatography (GC/LC)).
  3. The known and unknown compounds in the e-liquid or aerosol (mass spectrometry (MS)).
Fig 2. Ball-and-stick model of a Bromocresol Purple

The simplest and most commercially available method is to detect nicotine in e-liquid using Bromocresol Purple – pH indicator. The presence of nicotine in e-liquid significantly increases the pH of e-liquid. Based on this fact, adding Bromocresol Purple to e-liquid predicts the color changing from yellow to pink in the presence of nicotine. It is also convenient to use bromothymol strips in the laboratory, which are commercially available. But the indicator is more accurate and gives a more visually noticeable effect.

Chromatography and mass-spectrometry are more accurate but more expensive methods. Chromatography is a method of separating liquid or gaseous mixtures in which a substance is distributed between two phases: mobile and stationary. The mobile phase carries through a system (a column, a plate, a capillary tube, or a sheet) on which a material called the stationary phase is fixed. The test mixture is composed of constituents with different affinities for the stationary phase. Because of that some of them stay longer on the stationary phase while others stay shorter. It depends on their interactions with its surface sites. As a result, some constituents are detected earlier than others and they can be separated. Using a chromatogram it is possible to calculate the concentration of each constituent that is directly proportional to the area under the curve.

For a complete analysis of the components of the mixture, chromatography is performed in combination with mass spectrometry. It can be a combination of gas chromatography (GC) and mass spectrometry (MS) – GC/MS or liquid chromatography (LC) and mass spectrometry – LC/MS, as well as different variations depending on their design features.

Mass spectrometry (MS) is a method of determining the chemical composition and molecular structure of a substance based on the registration of the spectrum of ion masses formed as a result of ionization of atoms and/or sample molecules. The main characteristics of the method are: 1) mass spectrometers can identify only ions; 2) they are used to measure the mass-to-charge ratio of ions. The results are presented as a mass spectrum (a plot of intensity as a function of the mass-to-charge ratio) that are used to determine structure of molecules and the masses of particles and of molecules.

Overall, the combination of chromatography and mass spectrometry allows to perform fully characterization of e-liquid or aerosol composition to detect the presence of nicotine and others compounds.  Of course, these methods have their disadvantages, among which the most important for us is their non-portability.

Surface-enhanced Raman scattering (SERS) is a more portable method. It relies on the unique SERS spectrum of the analyte, enhanced by a suitable SERS-active substrate. In research by Chien et all (“Rapid identification of nicotine in electronic cigarette liquids based on surface-enhanced Raman scattering”), it was investigated this method to determine nicotine in e-liquid. For this purpose, it was prepared substrate made of silver nanoparticle arrays embedded in anodic aluminum oxide nanochannels (Ag/AAO) on which a droplet of e-liquid was put for analysis. The molecules were excited by a laser beam and then scattered radiation collected by the same lens was dispersed with a spectrograph to get a spectrum. Such experiments can be performed using Raman spectrometers.

Wrapping up

Overall, this article has described the methods of nicotine identification used today. Each of them has its advantages and disadvantages but allows one to accurately identify the presence of nicotine in the e-liquid or in the aerosol.

Don’t hesitate to contact us if you have any questions. We are here to share our expertise and provide cutting-edge equipment for your product development and QA.

Leave a Reply

Your email address will not be published. Required fields are marked *