Detection of concanavalin A receptors by affinity to peroxidase and iron dextran by scanning and transmission electron microscopy and x-ray microanalysis

Cytochemical applications of X-ray microanalysis

X-ray microanalysis (XRMA) has been applied to a wide variety of cytochemical problems, but the most valuable applications have been to the validation of cytochemical methods (by the qualitative or quantitative analysis of reaction products), and to the simultaneous localization of more than one substance, which cannot easily be achieved by using alternative methods. The latter applications involve stoichiometric studies (the quantitative relationships between reaction products and substrates), and distribution studies. Ultrastructural cytochemistry with XRMA is limited by the need to use high-brightness electron sources. Apart from the limited availability of such sources, they may cause unacceptable damage to the specimen. Preparation methods for cytochemistry using XRMA are reviewed; in principle these do not differ from those used for other cytochemical applications, but it is important not to introduce extraneous elements (from fixative, buffer, or embedding medium) into the specimen, where the additional X-ray peaks may interfere with the analysis. Quantification in XRMA of cytochemical preparations poses special problems, because the addition of the reaction product to the specimen alters the yield of continuum X rays, used for assessing the mass of the specimen, and also dilutes endogenous elements. However, measurement of ratios between characteristic elemental peaks is a useful method in X-ray microanalytical cytochemistry, and it is concluded that one of the most important attributes of XRMA for cytochemical purposes is the ease with which the substances of interest can be measured.

Quantitation in biological X-ray microanalysis, with particular reference to histochemistry

Thin specimens consisting of various light and heavy elements in gelatine have been subjected to X-ray microanalysis to determine the relationship between the number of X-ray counts for a specific element expressed as a percentage of the continuum (the percentage counts) and the concentration of that element. For light elements, the relationship between the percentage counts and concentration is strictly linear. For heavier elements, the relationship is not linear, because of the increase of the continuum counts with (formula: see text). If a correction is made for the effect of (formula:see text), heavy elements also show a linear relationship between percentage counts and concentration. Within the limits of atomic number (Z = 56) and concentration (approximately 10%) studied here, it is shown that when X-ray microanalysis is carried out on bulk specimens consisting of various elements in gelatine, the relationship between X-ray counts and concentration for a particular element is linear. The problems in quantitation of the results of X-ray microanalysis caused by exogenous continuum and mass loss induced by irradiation are discussed. It is pointed out that when X-ray microanalysis is used to study histochemical and other staining procedures, allowance must also be made for the reduction in concentration of other elements in the specimen as a result of the addition of the stain to the specimen.