Chemical mapping

Secondary ion mass spectrometry (SIMS) is by far the most sensitive surface teclmique, but also the most difficult one to quantify. SIMS is very popular in materials research for making concentration depth profiles and chemical maps of the surface. For a more extensive treatment of SIMS the reader is referred to [3] and [14. 15 and 16]. The principle of SIMS is conceptually simple When a surface is exposed to a beam of ions... 

As in Auger spectroscopy, SIMS can be used to make concentration depth profiles and, by rastering the ion beam over the surface, to make chemical maps of certain elements. More recently, SIMS has become very popular in the characterization of polymer surfaces [14,15 and 16]. 

Static SIMS is labeled a trace analytical technique because of the very small volume of material (top monolayer) on which the analysis is performed. Static SIMS can also be used to perform chemical mapping by measuring characteristic molecules and fiagment ions in imaging mode. Unlike dynamic SIMS, static SIMS is not used to depth profile or to measure elemental impurities at trace levels. 

In addition to data obtained using the spectral mode of analysis, it is often important to know the location of a particular chemical group or compound on the sample surface. Such information is achieved by static SIMS chemical mapping—a procedure in which a specific chemical functionality on the material is imaged, providing information as to its lateral distribution on the surface. 

The use of chemical mapping is demonstrated in the following example involving the delamination of a silicone primer and polytetrafluoroethylene (PTFE) material. The positive mass spectrum acquired from the delaminated interface contains peaks known to be uniquely characteristic of PTFE (CF3 at mass 69) and the silicone primer (Si(CH3)3 at mass 73). Figures 6 and 7 are secondary ion im es of the CF3 and (Si(CH3)3 fragments taken from a 1-mm area of the delaminated interface. These maps clearly indicate that the PTFE and the silicone primer exist in well-defined and complementary areas. 

Static SIMS has been demonstrated to be a valuable tool in the chemical characterization of surfaces. It is unique in its ability to provide chemical information with high surface sensitivity. The technique is capable of providing mass spectral data (both positive and negative spectrometry), as well as chemical mapping, thereby giving a complete microchemical analysis. The type of information provided by... 

Yuen et al. [24] first demonstrated the nature of the information that can be obtained regarding chemical mapping within a fixed-bed reactor, using the liquid phase esterification of methanol and acetic acid catalyzed within a fixed bed of H+ ion-exchange resin (Amberlyst 15, particle size 600-850-pm) catalyst as the model... 

As for sample preparation, SPE-GC has become more popular than NPLC-GC. Aqueous samples are not compatible with NPLC-GC, while RPLC-GC has never become a success. SPE-GC-(tandem)MS and SPE-GC-AED systems have demonstrated excellent performance. SPME is an equilibrium technique while SPE affords exhaustive extraction of the analytes. Laser desorption injection in LD-GC-MS can uniquely provide an additional dimension of spatial information for 2D surface chemical mapping [221]. 

In conclusion, AES is mainly used to study the elemental surface composition of conducting samples. It can be used to make chemical maps of heterogeneous surfaces and to study the vertical distribution of elements as a function of depth. The technique is of great importance in surface science and materials science, but less in the characterization of supported catalysts. 

SIMS is by far the most sensitive surface technique, but also the most difficult one to quantify. SIMS is very popular in materials research for making concentration depth profiles and chemical maps of the surface. The principle of SIMS is conceptually simple A primary ion beam (Ar+, 0.5-5 keV) is used to sputter atoms, ions and molecular fragments from the surface which are consequently analyzed with a mass spectrometer. It is as if one scratches some material from the surface and puts it in a mass spectrometer to see what elements are present. However, the theory behind SIMS is far from simple. In particular the formation of ions upon sputtering in or near the surface is hardly understood. The interested reader will find a wealth of information on SIMS in the books by Benninghoven et al. [2J and Vickerman el al. [4], while many applications have been described by Briggs et al. [5]. 

Taking the same approach as that described above, Chianelli et al. [72] doped a single crystal of MoS2 with cobalt and equilibrated it at high temperature. Chemical maps made with scanning Auger electron spectroscopy at a spatial... 

Chemical mapping of chemical conversion in heterogeneous catalytic 286 reactors using MRI... 

The structure of this review is as follows. Section II focuses on the basic principles of MRI techniques, and then more advanced techniques which have been used to study catalytic reactors will be introduced in Section III. To illustrate the use of these techniques examples will be given from the field of catalysis, although not necessarily at the scale of the reactor and, in some cases, data for model systems will be shown. Section IV describes methods used to achieve chemical mapping. Section V focuses exclusively on previous research which has used MRI techniques to spatially resolve chemical composition in fixed-bed reactors. 

In Section II.3 we have seen that a specific chemical species existing in a given physicochemical environment is characterized by specific values of 7) and T2, and that this fact is important both in the implementation of imaging pulse sequences to obtain quantitative information and in the modification of the pulse sequences to image selectively one species and/or phase within the sample. While exploitation of relaxation time contrast is not likely to become a routine approach for chemical mapping in reactors, there will be niche applications in which it will continue to have use—three of these are identified below. The limitations of the approach derive from that fact that the relaxation times characterizing a system will not only be influenced by chemical composition but also by temperature and the proximity of the molecules to a solid surface or interface. The three case studies illustrated below in which relaxation time contrast has been used with considerable success are (i) an... 

Chemical manufacturing sodium sulfide in, 23 639 key characteristics of, 11 440t safety in, 21 826-827 safety legislation related to, 21 827-828 Chemical mapping, AES, 24 106 Chemical Marketing Research Association (CMRA), 15 645-646 Chemical metallurgy, 16 126 Chemical methods... 

The exploration of other planets increasingly involves combining the detailed chemical analyses of samples (laboratory or in situ) with chemical mapping by orbiting spacecraft to provide geologic context. In this chapter, we illustrate this approach to exploration by reviewing what has been learned about the Moon and Mars. 

The plots of the intensities of selected characteristic bands as a function of lateral position (so-called chemical maps) provide information on the amount of the respective molecules or molecular groups in the different morphological structures (Fig. 4.2). The band at 784 cm 1 can be assigned to out-of-plane deformation vibrational modes of the nucleobases cytosine, thymine and uracil and serves as an indicator for the presence of nucleic acids. At 483 cm-1, a C-C-C deformation of carbohydrate polymers such as starch or pectin is present in some of the spectra. To study the distribution of protein compounds, we analysed characteristic signals of the amino acid phenylalanine (1002 cm 1 ring breathe) as well as of the protein amide I band (1651 cm-1) that is brought about by vibrations of the protein backbones. The maximum of the phenylalanine signal co-localizes with a maximum in protein content... 

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