Chemical images acquisition

Figure 4 Chemical images of a nickei TEM grid. Fieid of view is approximateiy 25 x 15 im, 50 X 50 pixeis. Analyticai conditions Ga sputtering, spot size about 0.2 pm, 24S-nm radiation, acquisition time 33 minutes.

FT Spectrometers FT spectrometers (Figure 3) differ from scanning spectrometers by the fact that the recorded signal is an interferogram [14] (see Chapter 6.2). They can be coupled to a microscope or macrochamber with an FPA detector. FT chemical imaging systems (CISs) are available for Raman, NIR, and IR spectroscopy. However, they can only be considered as research instruments. For example, most IR imaging systems are FT spectrometers coupled to microscopes. This type of spectrometer allows the acquisition of spectra in reflection, attenuated total reflection (ATR), or transmission mode. 

In addition to measurements of how much and what type of chemical species are present, modification of the MR experiment allows us to identify the physical state of a given species (e.g., gas, liquid, gel, and solid) and to quantify temperature and any incoherent and/or coherent transport processes within the system. By integrating any of these measurements into an imaging experiment, we can spatially map these quantities or exploit the effect of these characteristics on the magnitude or frequency of the MR signal to preferentially observe sub-populations of spins within the system. In this latter application we are exploiting the so-called contrast mechanisms in the image acquisition. These concepts are illustrated in Sections II.B II.D. 

The issues with respect to obtaining chemical information within an imaging experiment are considered next. The description of image acquisition given in Section II.A.l was based on the assumption that the Larmor frequency of a nuclear spin is directly related to its location in the sample, as determined by the applied magnetic field gradient. As discussed by Callaghan (13), this is precisely true only... 

An example of the application of RARE for rapid image acquisition is shown in Fig. 19, in which a single frame is shown from a series of 2-D images acquired of an oscillatory chemical reaction occurring within a fixed bed. Relaxation contrast is used to discriminate between the reaction products Mn " and Mn (49). In this example, MR offered the opportunity to map the detailed structure of the fixed bed and the product distribution within it. This pulse sequence has also recently been applied to obtain quantitative images of the evolution of a lysozyme urea separation within a chromatography column (50). 

Fig. 5.4. Raman imaging of a HeLa cell incubated for 28 h with Phe-d5. (A) Hierarchical cluster analysis image with five clusters. Univariate images of (B) nucleotides (770-790cm 1), (C) phospholipids (700-730cm 1), (D) Phe-d5 (950-965cm-1), (E) Phe-h5 (995-1, 005 cm-1), and (F) Phe-d5/Phe-h5 ratios (950-965 cm-1 region divided by the 995-1,005 cm-1 region). Image acquisition parameters Exposure time ls/pixel, step size 0.47pm/pixel, field of view 15 x 15 pm2 (reprinted with permission from [30]. Copyright 2008 American Chemical Society)...

Shown herein are the first 2D multiple-pulse NMR images following a chemical reaction for which the image contrast is Ti rather than T2. A multiple pulse line narrowing sequence is critical to efficient image acquisition where broad lines are expected. The gas-solid reaction between ammonia and a crystal of 4-bromobenzoic acid was monitored optically and by NMR imaging. Some anisotropy in the reaction... 

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