EDXA

W. Briiggemann, P. R. Moog, H. Nakagawa, P. Janiesch, and P. J. C. Kuiper, Plasma membrane-bound NADH-Fe -EDXA reductase and iron deficiency in tomato. (Lycopcrsicon escidentiim). Is there a turbo reductase Physiol. Plant 79 339 (1991). 

The withdrawn hquid-phase samples were analyzed with an HPLC (Biorad Aminex HPX-87C carbohydrate coluttm. 1.2 ttiM CaS04 in deionized water was used as a mobile phase, since calcium ions improve the resolution of lactobionic acid [17]). Dissolved metals were analysed by Direct Current Plasma (DCP). The catalysts were characterized by (nitrogen adsorption BET, XPS surface analysis, SEM-EDXA, hydrogen TPD and particle size analysis). 

Rapp etal. (1999) nsed electron energy loss spectroscopy (EELS) to study the microdistribution of MMF resin in the cell wall in Norway spruce. The authors noted that althongh SEM-EDXA was snitable for determining whether penetration into the cell wall had occurred, the relatively large excitation volnme precluded accurate quantitative determination of the distribntion of material in the cell wall. They therefore examined the suitability of TEM-EELS as a method for determining the cell wall distribntion of resin. The use of EELS in combination with TEM allows for determination of light elements, such... 

Saka and Yakake (1993) chemically modified wood samples with 3-isocyanatopropyl-triethoxysilane (IPTES) (Figure 7.9c). Wood was impregnated with acetone solutions of IPTES of different concentrations. Where the wood had been pre-swollen by treating with pyridine vaponr, a maximnm WPG of 27 % was obtained, whereas without pre-swelling of the cell wall a WPG of only 7 % was obtained. Pyridine also serves as a catalyst for the reaction of isocyanate with wood. SEM-EDXA showed the presence of silicon in the cell walls of the treated wood. Becanse of the lower WPG obtained without cell wall swelling, ASEs of the order of 20 % were obtained, compared to about 60 % when swelling of the cell wall was used prior to reaction. 

SEM-EDXA Scanning electron microscopy electron diffnse X-ray analysis... 

It is well known that the structure, distribution and properties of protolignin in cell walls vary according to cell type and morphological location. This is based upon extensive studies on topochemical properties of lignin using various methods such as ultraviolet microscopic photometry (1,2), bromination-SEM-EDXA (3) and other physical or chemical analyses of isolated tissue fractions (4). 

N. Schrage, J. Becker, White precipitation after FeHe endotamponade. ESEM and EDXA analysis. Presented at the First Meeting on Heavy Tamponades, Telfs, (2003). 

As the cornea physiologically contains almost no phosphate, we have found evidence that for an osmolar conditioning of the cornea, an electrolyte conditioning is highly probable. We could prove this by means of Energy dispersive X-ray analysis (EDXA) [16], With this method, we have found elevated phosphate contents in the cornea after rinsing one or several times with phosphate buffer [17], This reflects a situation of... 

Schrage, N.P., Benz, K., Beaujean, P., Burchard, W.G., Reim, M. A simple empirical calibration of energy dispersive X-ray analysis (EDXA) on the cornea. Scanning Microsc 7(3), 881-888 (1993)... 

In nature this common set is typically further restricted over wide geographic areas because of the influence or otherwise of soil-forming factors, the most important of which are parent material and degree of weathering. Thus, a typical sample of soil will contain a suite of around six to ten different major minerals. A major mineral may be defined as one that is present at a concentration of a few percent or more, at which it will be readily detectable by routine techniques such as x-ray provider diffraction (XRPD). It is also known as energy-dispersive x-ray analysis (EDXA) or energy-dispersive analysis of x-ray (EDAX) or microscopic examination, either optical or electron. It is also not uncommon for several other minerals to be present in any given soil but usually in amounts that put them below the routine detection limits of many techniques. Nonetheless, these accessory, or trace, minerals can often be concentrated by some means that separates the soil sample into different physical or chemical fractions. Such procedures effectively lower... 

Three quantitative approaches to measure lignin distribution are interference microscopy, UV microscopy, and bromination/EDXA. The choice of method probably depends more on the availability of equipment than any other factor since each method can be applied to a similar range of specimen types. 

Bromination/EDXA (Chap. 4.4) has several disadvantages when compared to the other two techniques. Only relative lignin concentration can be determined directly by this method and a correction factor of 1.7 is required to obtain agreement between techniques (Saka et al. 1982, Donaldson and Ryan 1987). When bromination/EDXA and interference microscopy are used on matched samples, agreement is poor (Donaldson and Ryan 1987) as shown in Table 4.3.2. Not only is there poor quantitative agreement between the two methods, but EDXA data are also much more variable within each specimen. 

Table 4.3.2. Relative lignin concentration (ccml/S2) for two matched samples determined by interference microscopy and bromination/EDXA. (Donaldson and Ryan 1987)...

One of the limitations of electron microscopy is that it allows only a visual characterization of the cell wall structure. Once electron microscopy is combined with energy dispersive X-ray analysis (EDXA), the system becomes a powerful analytical tool for elucidating the fine details of lignin morphology in wood. 

As applied to bromine, the X-rays generated when this element is bombarded with electrons are manifested in emission spectra as lines designated Br-Ka, Br-K/(, and Br-L (more precisely, La) which correspond to energy levels of 11.9, 13.3, and 1.48keV, respectively (Russ 1974). These characteristic lines for bromine can be used in EDXA analysis. 

The brominated sticks are embedded in Spurr epoxy resin (Spurr 1969) and sectioned with a diamond knife or glass knife mounted on an ultramicrotome to give cross sections of 0.15//m thickness for TEM-EDXA or 0.5//m thickness for SEM-EDXA. The sections are then placed on a carbon-coated collodion film on the specimen support grid. The specimens are carbon-coated again to avoid charging. 

The brominated specimens may be studied by a SEM-EDXA or a TEM-EDXA system. Since the intensity of the X-ray emission is directly proportional to the illuminating current, it is essential, for quantitative assay, to ascertain the current during the analysis. A Faraday cup (Howitt et al. 1976) in conjunction with an electrometer (e.g., Keithley 616 Digital Electrometer) may be used. The illuminating current should preferably be in the range of 10-9-10-11) amperes. 

Thin sections may readily be examined with TEM-EDXA or SEM-EDXA in the transmission mode (STEM-EDXA). However, to use conventional SEM-EDXA, some modifications of the equipment are required. As shown in Fig. 4.4.3, the electrons transmitted through a thin specimen impinge upon the carbon plate underneath. This causes the emission of a strong continuous spectrum of white X-rays. To minimize this problem, a carbon grid holder with a Faraday cup should be used. If the depth of the cylinder in the Faraday cup is more than 20 times the size of aperture, the electrons can be effectively collected (Grubb 1971, Howitt et al. 1976), thus reducing a large portion of the white X-rays emitted. 

Table 4.4.1 gives the distribution of lignin in Douglas-fir (Pseudotsuga menziesii) earlywood tracheids (Saka and Thomas 1982). The overall lignin content (W) of the earlywood portion is 0.285 gig). The Klason and acid-soluble lignin determinations should be made on wood taken near the location from which the sections are collected for EDXA measurements. 

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