Acid test for e-liquids

The use of citric acid in e-liquids needs to be investigated further to understand its potential to form potentially harmful anhydrides in electronic-cigarette vapor, according to a presentation given by British American Tobacco Scientists on Friday at the annual conference of the Society for Research on Nicotine and Tobacco in Florence, Italy.

‘Citric acid occurs naturally in the body, is “generally recognised as safe” in the USA, and is used in pharmaceutical inhalation products,’ BAT said in a press note. ‘However, thermal degradation of citric acid can occur at the operating temperatures of some vaping devices. Starting at around 175-203° C, citric acid can degrade to form citraconic anhydride and its isomer itaconic anhydride.

‘These anhydrides are respiratory sensitizers—chemicals that, on inhalation, can trigger an allergic reaction varying from hay fever symptoms to anaphylactic shock.’

The scientists used gas chromatography coupled to time-of-flight mass spectrometry to analyse the vapor generated when an e-liquid containing citric acid is heated in a vaping device. The device used was a first-generation (cig-a-like) e-cigarette. The scientists were reported to have been able to measure significant amounts of anhydrides in the vapour.

“Citric acid in an e-liquid may lead to significant amounts of citraconic and/or itaconic anhydride in vapor, depending on the device,” said Dr. Sandra Costigan, principal toxicologist vaping products.

“But we believe that flavorings can be used responsibly and we have already rejected the use of some flavorings in our products. Based on this case study using a first-generation e-cigarette, we recommend that the potential for formation of citraconic and itaconic anhydrides should be investigated further before commercialisation of e-liquids containing citric acid.”