Correction for extraneous background in X-ray microanalysis of cell cultures

Some practical aspects of the X-ray microanalysis of cell cultures have been investigated. Cells were cultured on titanium grids covered with Formvar films and analyzed at 100 kV either in the scanning transmission (STEM) or transmission mode (TEM) of the electron microscope. Different holders, grids and configurations were compared with respect to the relative contribution of different factors to the extraneous background in the X-ray spectrum. When low atomic number holders are used, the contribution to the spectrum of electrons scattered through high angles, may be negligible. In practice this may result in negative values for the contribution of these scattered electrons to the background. Computer programs for correction of the extraneous background should ignore these negative values and replace them by zero. When a brass holder is used, the contribution to the spectrum from electrons scattered through high angles becomes more important than that of the uncollimated radiation. The position of the analyzed cell relative to the grid bars is more important than the choice of grid or holder type. The data show that for the specimens used in the present study the correction for extraneous background is of little importance and can be neglected.