Any other than what? At least 2012 published article by yoon et al describes one method. Available at Talanta. 2012 Aug 15;97:256-61. doi: 10.1016/j.talanta.2012.04.027. Epub 2012 May 14.
A new method for quantifying N-nitrosamines in wastewater samples by gas chromatography-triple quadrupole mass spectrometry.