Zheng, Sai-Jing, et al. “Rapid Determination of Four Tobacco-Specific Nitrosamines in Mainstream Cigarette Smoke by UPLC-TOF-MS”. Asian Journal of Chemistry, vol. 24, no. 3, Dec. 2011, pp. 1147-50, https://asianpubs.org/index.php/ajchem/article/view/8728.