EELS, analytical method

Table 5.2 Summary of selected analytical methods for molecular environmental geochemistry. AAS Atomic absorption spectroscopy AFM Atomic force microscopy (also known as SFM) CT Computerized tomography EDS Energy dispersive spectrometry. EELS Electron energy loss spectroscopy EM Electron microscopy EPR Electron paramagnetic resonance (also known as ESR) ESR Electron spin resonance (also known as EPR) EXAFS Extended X-ray absorption fine structure FUR Fourier transform infrared FIR-TEM Fligh-resolution transmission electron microscopy ICP-AES Inductively-coupled plasma atomic emission spectrometry ICP-MS Inductively-coupled plasma mass spectrometry. Reproduced by permission of American Geophysical Union. O Day PA (1999) Molecular environmental geochemistry. Rev Geophysics 37 249-274. Copyright 1999 American Geophysical Union...

For the supermolecules with periodic ordered structure, electron diffraction is an indispensable analytical method of TEM. Electron diffraction pattern contains information on the crystal structure, lattice repeat distance, and specimen shape. The pattern is always related to the image of the area of the specimen. There are basically two types of electron diffraction methods, selected area electron diffraction (SAED) and nanobeam electron diffraction (NEED), in which size of the area is of submicrometer scale in the former and of nanometer scale in the latter. In addition, two spectroscopic measurements done by using the TEM apparatus, EELS and EDS, are effective for structural analysis of the specimen. 

This kind of estimation of the relative concentration is the most widely used method for quantitative EELS analysis. It is advantageous because the dependence on the primary electron current, Iq, is cancelled out this is not easily determined in a transmission electron microscope under suitable analytical conditions. Eurthermore, in comparison with other methods, e. g. Auger electron spectroscopy and energy-disper-... 

A similar HPLC technique was employed for the investigation of the persistence of MG in juvenile eels (Anguilla anguilla). Extracts were separated in phenyl-hexyl and octyl silica columns (both 50 X 4.6 mm i.d. particle size 3 jun) in series. The mobile phase was composed of 60 per cent ACN and 40 per cent 0.05 M ammonium acetate buffer (pH = 4.5). The flow rate was 0.6 ml/min and analytes were detected at 620 nm. The concentrations of MG and LMG are compiled in Table 3.16. The data prove that this HPLC method can be used for the investigation of the persistence of MG and LMG in animal tissues [106],... 

For example, in eel, high concentrations of polychlorinated biphenyls can be present and can interfere in the cleanup procedure. Fly ash is difficult to extract. Drastic concentration and cleanup procedures such as saponification can convert some isomers. Oc-tachlorodibenzo-p-dioxin can easily be broken down during the cleanup procedure. For each matrix a specific isolation technique is necessary. The method has to be validated for all the isomers of the analytical program (24). 

Current methods used to image MCM-41 include (1) analytical transmission electron microscopy (TEM) to determine structure, size, morphology, and local chemical composition (2) energy-dispersive X-ray spectroscopy (EDXS) in a scanning electron microscope (SEM) to determine chemical composition 5 and (3) electron energy loss spectroscopy (EELS) for elemental analysis.6... 

During this optimisation programme, samples of eel, fish oil, mussel and sewage sludge were prepared for intercomparison. Data from analysis of a crude eel extract and a refined (cleaned-up) sample were compared to test the variance associated with different methods of sample preparation. The clean-up methods included gel permeation chromatography, saponification, concentrated sulphuric acid treatment, alumina and silica-gel column chromatography. The differences in results of the within and between clean-up methods did not significantly influence the overall analytical variance after the appropriate optimisation. 

Generally, the sensitivity of X-ray spectrometrie methods is not suffieient for direct measurement of PGE in environmental samples. However, adequate total reflection X-ray fluorescence (TXRF) methods have been developed to enable, after adequate sample preparation and analyte enrichment via Hg-coprecipitation, PGE-determination in various samples like road dust, airborne particles or liver and kidney tissue of exposed European eels (Anguilla anguilla) (Messerschmidt et al. 2000 Sures et al. 2001). 

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