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.

中文翻译：

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临界胶束浓度附近表面活性剂定量分析中液相色谱-串联质谱校准曲线的异常行为


包括季铵化合物在内的表面活性剂作为消费化学产品的一部分广泛应用于日常生活中，最近还应用于页岩油行业。由于其独特的两亲特性，表面活性剂在浓度高于某个阈值（称为临界胶束浓度 (CMC)）时形成胶束。 Siuzdak 等人之前进行的电喷雾电离质谱研究。等人提供了有关胶束形成的间接证据。在此，我们使用液相色谱-串联质谱法来探索这种胶束形成如何影响表面活性剂的定量分析。结果显示，一些选定的阴离子和阳离子表面活性剂的校准图中存在异常行为，例如癸基硫酸钠 (SDeS)、十二烷基硫酸钠 (SDS)、肉豆蔻基三甲基溴化铵 (MTAB) 和苄基二甲基十八烷基氯化铵 (BAC-18)。当浓度接近这些表面活性剂各自的 CMC 时，MTAB 的校准图变平，而 SDeS、SDS 和 BAC-18 的校准图的斜率突然发生变化。这些异常行为可能与胶束形成有关。从实践角度来看，上述观察结果表明，在表面活性剂的定量分析中，应避免接近CMC的高胶束浓度，以获得准确的表面活性剂测量结果。