Surfactants, including quaternary ammonium compounds, are widely used in daily life as part of consumer chemical products and, more recently, in the shale oil industry. Because of their unique amphiphilic properties, surfactants form micelles at concentrations above a certain threshold known as the critical micelle concentration (CMC). A previous electrospray ionization mass spectrometry studies conducted by Siuzdak et al. and others presented indirect evidence regarding micelle formation. Herein, we have used liquid chromatography–tandem mass spectrometry to explore how such micelle formations affect the quantitative analysis of surfactants. Results reveal abnormal behaviors in the calibration plots of a few selected anionic and cationic surfactants, such as sodium decyl sulfate (SDeS), sodium dodecyl sulfate (SDS), myristyltrimethylammonium bromide (MTAB), and benzyldimethyloctadecylammonium chloride (BAC-18). At concentrations close to the respective CMCs of these surfactants, the calibration plot for MTAB flattened, whereas the slopes of the calibration plots for SDeS, SDS, and BAC-18 suddenly changed. These abnormal behaviors can be related to micelle formation. From a practical perspective, the above observations suggest that in the quantitative analysis of surfactants, high micelle concentrations close to the CMC should be avoided to obtain accurate surfactant measurements.
Bibliographical noteFunding Information:
This work was supported by grants from the National Research Foundation of Korea (NRF) funded through Basic Science Research Program (2018R1A6A1A03024940 and 2018R1A2B6005707) and also by Korea Environment Industry & Technology Institute (KEITI) through Technology Program for Establishing Biocide Safety Management (2018002490001) and Technology Development Program for Safety Management of Household Chemical Products (2020002960004), funded by Korea Ministry of Environment (MOE).
© 2020 John Wiley & Sons, Ltd.
- mass spectrometry
- micelle formation concentration (CMC)
- quaternary ammonium compound (QAC)
ASJC Scopus subject areas