Development of a direct analysis technique for organic compounds adsorbed on environmental small particles

最近，内分泌干扰物引起了人们的极大关注。由于许多这样的物质是疏水性的，而且蒸汽压很低，环境中的小颗粒被认为是内分泌干扰物的载体。因此，建立合适的分析技术来分析吸附在小颗粒上的有机物是非常重要的。飞行时间二次离子质谱仪(TOF-SIMS)是最灵敏的表面有机物分析技术之一。镓聚焦离子束是目前TOF-SIMS中最常用的一次离子束，利用这种精细聚焦的一次离子束，作图分析的横向分辨率可达到亚微米级。作者考察了TOF-SIMS在单个小颗粒上吸附的有机物种分析中的适用性，以评估该技术作为环境分析工具的可行性。邻苯二甲酸二(2-乙基己基)酯、邻苯二甲酸二辛酯和2，2-二(4-羟基苯基)丙烷…更多的(双酚-A)作为模型化合物。这些化合物都被怀疑是内分泌干扰物。首先，每个化合物大约1个单分子层被吸附在平板基质上，而不是颗粒上，并测量了质谱图。衬底是银、覆盖有自然氧化物的硅和石墨。尽管银衬底的光谱强度要高得多，但所有衬底的碎裂模式都是相似的。两种邻苯二甲酸二烷基酯在m/z=149处产生了最强的碎片峰，这是邻苯二甲酸酯的特征。烷基链源的碎片峰在光谱中很弱，由于碳氢化合物的污染，很难被指认。因此，很难区分邻苯二甲酸酯的异构体。双酚-A在m/z=213处出现特征碎片峰。然后，将邻苯二甲酸二(2-乙基己基)酯或双酚-A浸泡在6.8微米的二氧化硅颗粒上。这些颗粒被烘干，然后铺在玻璃盘上。通过将铟片压在颗粒上，制备了TOS-SIMS样品。光谱测绘以256x256像素分辨率在50微米的平方面积上进行。从二维谱图数据中得到了Si^+(m/z=28)、In^+(m/z=115)、邻苯二甲酸盐碎片离子(m/z=149)和双酚A碎片离子(m/z=213)图谱。In^+和Si^+表现出互补图谱。碎片离子的分布与Si~(++)相同。另一个样品是分别制备的颗粒的混合物，一个吸附邻苯二甲酸盐，另一个吸附双酚-A，在铟平板上。在混合样品的一个视场中，通过比较碎片离子图，可以区分出两种粒子。较少

Large attention has been paid recently to endocrine disrupting chemicals. Because many of such substances are hydrophobic and of low vapor pressure, environmental small particles are believed to act as carrier of endocrine disrupters. Therefore, it is very important to establish techniques appropriate to analyze organic species adsorbed on small particles. Time-of-flight secondary ion mass spectrometry (TOF-SIMS) is well known as one of the most sensitive analytical techniques applicable for surface organic species. Gallium focused ion beam is now the most popular primary ion beam of TOF-SIMS.By using this finely focused primary ion beam lateral resolution of mapping analysis reaches to sub-micrometer region.The authors examined the applicability of TOF-SIMS to the analysis of organic species adsorbed on individual small particles in order to evaluate the technique as an environmental analytical tool. Di (2-ethylhexyl) phthalate, dioctyl phthalate and 2, 2-bis (4-hydroxyphenyl) propane … More (bisphenol-A) were used as model compounds. All of them are suspected as endocrine disrupters.First, about 1 monolayer of each compound was adsorbed on flat substrates instead of particles, and mass spectra were measured. Substrates were silver, silicon covered with native oxide, and graphite. Although spectral intensity was much higher on silver substrate, fragmentation pattern was similar for all substrates. Both of dialkyl phthalates yielded the most intense fragment peak at m/z=149, which is characteristic of phthalates. Alkyl-chain-originated fragment peaks were weak in the spectra and were difficult to assign because of hydrocarbon contamination. Therefore, distinction of phthalate isomers was difficult. Bisphenol-A showed characteristic fragment peak at m/z=213.Next, di (2-ethylhexyl) phthalate or bisphenol-A was adsorbed on 6.8 micrometer silica particles by dipping the particles into dilute solutions. The particles were dried and spread on a glass plate. By pressing an indium plate onto the particles TOS-SIMS samples were prepared. Spectral mapping was performed over 50 micrometer square area by 256x256 pixel resolution. From the 2-dimensional spectral map data Si^+(m/z=28), In^+(m/z=115), phthalate fragment ion (m/z=149), and bisphenol-A fragment ion (m/z=213) maps were obtained. In^+ and Si^+ showed complementary maps with each other. Fragment ions showed the same distribution as Si^+.Another sample was the mixture of separately prepared particles, one adsorbed phthalate and the other bisphenol-A, on an indium plate. In a view field of the mixture sample two kinds of particles were distinguished from each other by comparing fragment ion maps. Less