The impact of 2, 4-dinitrophenylhydrazine (DNPH) background in the determination of carbonyls compounds in e-cigarette vapor
Carbonyl compounds, are known to be present in some e-liquid formulations and can be formed during aerosol generation. Analysis of these compounds, as their hydrazones (2,4-dinitrophenylhydrazine; DNPH) are routinely performed using high performance liquid chromatography (HPLC) with either ultraviolet (UV) or tandem mass spectrometry (MS/MS) detection. However, the variability associated with the background carbonyl levels found in the DNPH solutions, can impact the interpretation of analytical data, particularly in long term stability and simulated use studies. Differences in background carbonyl levels have been found amongst DNPH suppliers, as well as variability from lot-to-lot and container-to-container. In recent years, increased background levels of carbonyls have been found for formaldehyde, acetaldehyde, acetone and methyl ethyl ketone (MEK). Background carbonyl levels (on a µg/collection basis) have ranged from 1.4 to 12.2 for formaldehyde, and non-detected to 10.7 for acetaldehyde. When analyzing low delivery products, it is increasingly difficult to distinguish between the background levels from the DNPH solution, background associated with the vaping environment, and that generated by the product during the vaping process. Consequently, DNPH is routinely re-crystallized in the laboratory. Although this can reduce levels of some compounds like formaldehyde, other compounds such as acetone and MEK may be present in trace amounts in the solvents used during the recrystallization process, increasing the background levels. Purchasing of a custom DNPH recrystallized 5 times by the supplier, was found to have comparatively low amounts of formaldehyde and acetaldehyde. DNPH hydrochloride has been evaluated as another approach to background reduction with some success.