It is generally accepted that e-liquids and e-cigarette vapor may contain mono- and dicarbonyls. This class of compounds derive either from propylene glycol, glycerol or flavor substances in e-liquids or from thermal degradation during the vaping process. Since some of the mentioned carbonyls are toxic, there is great interest to investigate their levels in emissions, especially from reduced risk products.

In this work we present the development and validation of an analytical method which is capable to quantitatively determine twelve monocarbonyls (formaldehyde, acetaldehyde, crotonaldehyde, propionaldehyde, butyraldehyde, acetone, acrolein, 2-butanone, benzaldehyde, cinnamaldehyde, acetoin, acetol) as well as four dicarbonyls (glyoxal, methylglyoxal, diacetyl, 2,3-pentanedione) in e-liquid and e-cigarette vapor. The large number of analytes in combination with their presumably low concentrations provides the need for a highly selective and sensitive analytical method such as high-performance liquid chromatography coupled to electrospray ionization tandem mass spectrometry (HPLC-MS/MS) operating in negative mode. Prior to injection, e-liquid and e-cigarette vapor samples were diluted with 2,4-dinitrophenylhydrazine for derivatization. Within 23 min total chromatographic run time, 16 carbonyls together with their corresponding isomers could be unambiguously identified. Four isotope-labelled internal standards were monitored to control the reproducibility of the sample preparation and analytical method.

The described method was comprehensively validated showing reasonable results regarding recovery (e.g. 83-126 % in e-cigarette vapor) or reproducibility (e.g. inter-day RSD for e-liquid <20 %, except glyoxal). In one of the selected e-liquid samples glyoxal, methylglyoxal and acetol could be detected at concentrations of 8.4, 25 and 9.6 µg/g e liquid, respectively. Vaping of the same e-liquid according to CRM 81 using a closed tank-system as device provided the following results: glyoxal, methylglyoxal and acetol at concentrations of 0.4, 2.6 and 1.5 µg per 25 puffs each, respectively.

In summary, a straightforward, robust, sensitive, selective and reliable method for the determination of 16 carbonyls in e-liquid and vapor of e-cigarettes has been developed and validated.