ELIQUIDS & VAPOUR

Identifying the correspondence between what is present in the liquid and what is present in its vapour both qualitatively and quantitatively required finding a method of analysis that would allow the chemistry and physics of vaping to be codified.

WHAT HAPPENS TO ELIQUIDS WHEN THEY BECOME VAPOUR

The activities carried out in recent months for the analysis of eliquids, thanks to the use of state-of-the-art instrumentation used in health analytics, have led us to an in-depth understanding of inhalation liquids, or rather of the vapour produced by them when vaping. The project we had set up in late spring 2016 in fact wanted not only to identify the emissions of certain substances being monitored in the run-up to the European TPD legislation, but above all to understand how and what happens in the phase transition between the liquid and its vapour. Identifying the correspondence between what is present in the liquid and what is present in its vapour both qualitatively and quantitatively required finding a method of analysis that would allow the chemistry and physics of vaping to be codified.

SPME systems because we could not consider them physically similar to the vaping we know and use. In fact, the dynamic condition of vapour production, both from the point of view of flow and the way in which the vaporisers are activated, did not allow us to identify in these almost-static techniques the realistic experimental conditions we wanted to reconstruct. The absorption and de-absorption phases in the solid matrix then made the measurement not exactly reliable..

Instead, the system we have developed uses a mass-mass system which, with an electrospray system at its head, makes it possible to ionise the vapour at atmospheric pressure (API - Atmospheric Pressure Ionisation), sending the saturated flow of ions into HPLC and identifying all the elements (compounds) present and also quantifying them.

To do this, we used a single-coil atomiser driven by a DNA 75 circuit controlling temperature and monitoring and managing the puffs simulating 'vaping' with Escribe, a calculation for the sizing of the vacuum pump needed to send the vapour into the ionisation chamber allowed us to simulate a human-type suction and above all to obtain repeatability and determinability of the tests.

The duration of the puffs was optimised with the input of external air as well (which reproduces the condition of the Venturi effect relating to the input of humid air taken from an environment with controlled temperature and humidity) in order to avoid the obscuration of the system due to excess vapour, which in the first experimental moments did not allow us to operate the system correctly due to the high sensitivity of the machine. The problem of dilution of the analytes is in fact generally one of the most delicate elements to be fine-tuned in the definition of gas chromatography methods.

The work done synergistically by Nutrogenomics and ISB was absolutely fantastic. The results obtained also gained the interest of Bruker who is the manufacturer of the SACI/ESI system modified in a proprietary sense and already subject of a previous patent by ISB.

The starting method was the SANIST patented technology for biological and chemical analytical applications in the health field (Patents no. 7,368,728; Patents no. 8,232,520) and already in service at the Istituto dei Tumori and other hospital facilities such as the Desio Hospital.

This was a necessary premise, now I will try to explain this work better and practically.

The first thing that should be pointed out is that the analytes subjected to the tests, given that this is a generally widespread situation, can even before the fragmentation that occurs in the source, separate into ions due to the vaporisation process. The tendency due to conservative chemical and physical principles, leads to the identification of ions whose molecular mass is the sum of the molecule from which they are derived, taking into account the energy administered, this is absolutely normal for this to happen during GC/MS analysis, but the most interesting fact is that part of the fragmentation into ions we have discovered is also due to their vaporisation, i.e. the energy supplied by the vaping system. Basically, some molecules that were certainly present in the liquid were no longer present in their original form in the vapour but only their fragmented ions could be found. The figure shows an example of what happens to nicotine:

We have analysed other analytes e.g. melatonin, discovering in this case that it was not possible to make it 'fly' except by using a carrier with more VG but still in very modest quantities and in a slightly reduced ionic form that did not correspond precisely to the molecule being identified.

To exemplify, imagine a container in which a carrier, water, a neutral base or a solvent is immersed with many coloured balls of different materials representing the molecules (flavours, nicotine, other compounds...) present in a vaping mixture. There will be lighter 'balls' that will be able to 'fly' carried by the carrier, others that will stay where they are and still others that will break into fragments that will be able to 'fly'. A different carrier will achieve different results. This is why it is by no means certain that what is found in the liquid will be found as it is in the vapour, and still less that what is known to be present in a solution at a given level will vaporise completely and congruently with the amount present in the liquid. The conditions of vaping, the carrier (the base used) significantly influence the results and these are also unpredictable. We often speak of toxic substances found in inhalation liquids but often stop at the analysis of the liquid from the point of view of the chemical preparation alone, the TPD has rightly placed the focus on what we actually inhale, i.e. the vapour in the mix of compounds that make it up.

The preceding reminder is intended to refer in particular to such articles, even of recent publication, which have highlighted generalist statements that are not supported by adequate scientific arguments; it goes without saying that the press often does not consider it useful to delve into the arguments, either intentionally or due to inability, before making the information public. The validation of the source and methods should be the first element in providing correct information and not causing instrumental alarmism.

Today, in fact, the methods for analysing inhalation liquids, although not yet framed in specific ISO standards, can be carried out consistently with the physics of vaping and not just analytical chemistry.

On the basis of the sensitivity and the method of analysis constructed, we have then defined instrumental cut-off levels that take into account both the internal standard of the machine used and the vaping system, allowing us to disregard analytes present below the defined thresholds, bearing in mind that their standard deviation is evaluated proportionally to the aforementioned thresholds and can therefore modify either positively or negatively the absolute value of the concentration of the analyte considered. These compounds cut into the vapour can certainly be present in minute thresholds in the liquid phase, but what use is it to us to know this if not for scientific culture? Eliquids are inhaled, not drunk.
The cut-off thresholds have been assessed taking into account certain elements of both technological and physical nature:
    •    inspired air volume and actual inhalation concentration of the analyte considered;
    •    internal standard selected for the operation of the mass/mass system;
    •    significance of the sampled values;
Analyses of vapour emissions produced by BlendFEEL liquids and notified to the EU-ECG portal are available here.

This was our approach, and the method derived from it, is driving us to enthusiastically carry out studies and verifications on the blends used for bases, e.g. to assess the development of acrolein depending on the percentage of VG present and the way the system is used. The Escribe module used to drive the coil was very useful, it seemed to be designed specifically for this purpose, and knowing the amount of energy administered and the molecular interaction in confined and reduced spaces and its effect allowed us to open up other scenarios which we will tell you about shortly.