USE OF ULTRA-THIN WINDOW DETECTORS FOR BIOLOGICAL MICROANALYSIS

Films and bulk samples of Nylon, gelatin, Makrofol, epoxy resin, aminoplastic resin and sodium acetate have been used as models of biological samples. It is shown that the use of ultrathin window (UTW) detectors in scanning transmission and scanning electron microsopes permits the quantitative analysis of light elements, yielding a total element analysis with hydrogen estimated by difference or ''guesstimated''. Comparison with known concentrations or concentrations obtained by chemical analysis shows that X-ray microanalysis of sections by the peak to continuum ratio model and bulk samples by the phi(pz) model gives sufficiently accurate results for biological purposes. It is also shown that sections may be analysed by the standardless ratio model. The application of UTW detectors to total element analysis by quantitative elemental imaging is demonstrated of bulk biological samples, which have been freeze-substituted, embedded in epoxy resin and surface polished. The possibility of imaging the oxygen content of frozen-hydrated bulk tissue samples which have been surface polished is also demonstrated. This may lead to the imaging of water distribution in frozen-hydrated bulk samples of biological tissues. UTW detectors are also useful for detecting mass loss in organic samples by monitoring the decrease in oxygen 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.