Elemental composition of pyroantimonate precipitates analysed by electron spectroscopic imaging (ESI) and electron energy‐loss spectroscopy (EELS) in vitellogenic ovarian follicles of Drosophila

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Abstract
Ca2+ was precipitated with potassium antimonate in vitellogenic follicles of the fruit fly Drosophila melanogaster and the distribution of the precipitates formed was studied by electron microscopy. The microvilli of the oolemma in mid‐ and late vitellogenic follicles were lined with precipitates. The chemical composition of the precipitates was analysed by electron spectroscopic imaging (ESI). The images produced by inelastically scattered electrons at specific ionization edges were compared, and the nonspecific background signals were subtracted by an image processing system. The presence of Ca2+, antimony and oxygen in the precipitates formed could be demonstrated. The elemental composition of the precipitates and of yolk spheres was also analysed by electron energy‐loss spectroscopy (EELS). With respect to the precipitates, signals at the calcium L2,3‐edge, the oxygen K‐edge and the antimony M4,5‐edge were recorded without deconvolution and background subtraction. The yolk spheres, which were free of precipitates, gave the characteristic signal of the nitrogen K‐edge. The applied techniques combine good ultrastructural resolution with the possibility of analysing the elemental composition of histochemical reaction products and cellular structures.