USE OF ULTRA-THIN WINDOW DETECTORS FOR BIOLOGICAL MICROANALYSIS

Films and bulk samples of Nylon, gelatin, Makrofol, epoxy resin, amino plastic resin and sodium acetate have been used as models of biologica l samples. It is shown that the use of ultrathin window (UTW) detector s in scanning transmission and scanning electron microsopes permits th e quantitative analysis of light elements, yielding a total element an alysis with hydrogen estimated by difference or ''guesstimated''. Comp arison with known concentrations or concentrations obtained by chemica l analysis shows that X-ray microanalysis of sections by the peak to c ontinuum ratio model and bulk samples by the phi(pz) model gives suffi ciently accurate results for biological purposes. It is also shown tha t sections may be analysed by the standardless ratio model. The applic ation of UTW detectors to total element analysis by quantitative eleme ntal imaging is demonstrated of bulk biological samples, which have be en freeze-substituted, embedded in epoxy resin and surface polished. T he possibility of imaging the oxygen content of frozen-hydrated bulk t issue samples which have been surface polished is also demonstrated. T his may lead to the imaging of water distribution in frozen-hydrated b ulk samples of biological tissues. UTW detectors are also useful for d etecting mass loss in organic samples by monitoring the decrease in ox ygen counts and for detecting contamination by monitoring the increase in carbon counts. It is also shown that changes in carbon counts are good indicators of folds in sections.