Burns Sarah A, Valint Paul L, Gardella Joseph A
Department of Chemistry, University at Buffalo, State University of New York, Buffalo, New York 14260, USA.
Langmuir. 2009 Oct 6;25(19):11244-9. doi: 10.1021/la902343r.
Aggregation patterns and fragmentation ion data from thin film preparations of the anionic surfactant sodium bis(2-ethylhexyl) sulfosuccinate (aka Aerosol-OT (AOT)) near the critical micelle concentration (CMC) in carbon tetrachloride were determined using time-of-flight secondary ion mass spectrometry (ToF-SIMS). Previous work using electrospray ionization (ESI) and matrix-assisted laser desorption/ionization (MALDI) mass spectrometry to determine the chemical structure of AOT aggregates was compared to data from ToF-SIMS results from both positive and negative ion spectra. Quasi-molecular ions were detected for AOT in the positive and negative spectra at m/z 467 and 421, respectively, corresponding to [AOT+Na]+ and [AOT-Na]-. Repeating ion patterns assigned to AOT aggregates were detected in the positive spectra from n=3 to n=13, corresponding to the repeating series [AOTn+Na]+. A similar pattern [AOTn-Na]- was observed in the negative ion spectra from n=4 to n=14. ToF-SIMS analysis was also able to detect a previously unreported fragmentation pattern in the mass region below [AOT3+Na]+ when the film was cast from a solution with AOT concentration above the CMC. This pattern is observed starting at m/z 526 and continuing until the n=3 AOT is reached at m/z 1356 in the positive spectra. The pattern of ions is assigned to structures related to the sodium and sulfate ions from the headgroups of an aggregate of AOT molecules. The formation of the low mass pattern is shown to respond only to concentrations above the CMC, and allows for a more precise determination of CMC than previously reported methods. The CMC of AOT in carbon tetrachloride is shown to be between 2.0x10(-5) and 3.0x10(-5) molar.
使用飞行时间二次离子质谱（ToF-SIMS）测定了阴离子表面活性剂双（2-乙基己基）磺基琥珀酸钠（又名气溶胶-OT（AOT））在四氯化碳中接近临界胶束浓度（CMC）时薄膜制剂的聚集模式和碎片离子数据。将先前使用电喷雾电离（ESI）和基质辅助激光解吸/电离（MALDI）质谱法测定AOT聚集体化学结构的工作与正离子和负离子光谱的ToF-SIMS结果数据进行了比较。在正谱和负谱中分别在m/z 467和421处检测到AOT的准分子离子，分别对应于[AOT+Na]+和[AOT-Na]-。在正谱中从n=3到n=13检测到分配给AOT聚集体的重复离子模式，对应于重复系列[AOTn+Na]+。在n=4到n=14的负离子光谱中观察到类似的模式[AOTn-Na]-。当薄膜从AOT浓度高于CMC的溶液中浇铸时，ToF-SIMS分析还能够在质量区域低于[AOT3+Na]+处检测到先前未报道的碎片模式。这种模式从m/z 526开始观察到，一直持续到正谱中在m/z 1356处达到n=3的AOT。离子模式被分配给与AOT分子聚集体头基中的钠离子和硫酸根离子相关的结构。低质量模式的形成仅对高于CMC的浓度有响应，并且比先前报道的方法更精确地确定CMC。结果表明，AOT在四氯化碳中的CMC在2.0×10^(-5)至3.0×10^(-5)摩尔之间。
