Light element X-ray microanalysis in biology.

Abstract

It is shown that both qualitative and quantitative light element X-ray microanalysis of biological samples is feasible. These analyses were carried out using ultrathin window (UTW) detectors. Quantitative analysis yields a total element analysis with H estimated by difference or "guesstimated". Comparison with calculated concentrations, or concentrations obtained by chemical analysis, shows that X-ray microanalysis of sections, by the peak to continuum ratio model, give sufficiently accurate results for biological purposes. The measurement of O concentrations to yield water content is carried out using x-ray imaging techniques, so that the distribution of heavier elements can be spatially related to water and dry mass distribution. Similarly light element and heavy/light element ratios are readily visualised by X-ray imaging. These ratios can indicate the subcellular distribution of different molecular species e.g., nitrogenous compounds such as urates. It is possible to derive quantitative images of water distribution in both sections and bulk samples. Comparisons of the same sample type both as frozen sections and frozen bulk samples show that the water estimates obtained by the two different analytical methods are similar. Oxygen analysis of C films at different specimen temperatures unequivocally reveals the temperature at which ice deposition on the specimen commences. This establishes safe conditions for reducing mass loss in model samples and freeze-dried sections to minimal levels and for avoiding artefactual oxygen analyses of both frozen-hydrated and freeze-dried sections.