The analysis of isotopically labeled propylene glycol in e-cigarettes
Measurement of the excipients in e-cigarettes has become a hot topic of discussion with the release of the new draft guidance from the United States Food and Drug Administration (FDA). However difficulties in the selective measurement of the bioavailable portion of the excipients have allowed questions regarding the reduced health risk of e-cigarette use to remain open and nebulous to resolve. One of the commonly maligned chemicals is the carrier agent, propylene glycol. Despite the warnings from popular media and less popular politicians, propylene glycol (also found in soft drinks, ice cream, deodorant, cosmetics, and M&Ms) is identified by the FDA as safe for consumption at reasonable levels over long periods of time.
To date, methods validated for the measurement of propylene glycol in blood matrix have been confounded by significant interference of dietary and common lifestyle exposures. Measurements of basal levels of propylene glycol in plasma from healthy non-smokers (and non-vapers) range from 200 to 13,000 ng/ml. With this broad range of exposure there is no measurable difference between vapers and non-vapers.
We have developed a novel approach to the clinical testing of e-cigarettes which includes either propylene glycol or glycerin or both as a carrier for nicotine delivery. By utilizing carbon heavy propylene glycol as the carrier agent in the e-cigarette all dietary and lifestyle related exposures of non-labeled propylene glycol in plasma can be separated during mass spectrometry analysis. With this approach the question of propylene glycol bioavailability from each model, dose and dose period can be answered. Furthermore, this approach will be able to unequivocally determine the second hand exposure to e-cigarettes.