Beam induced mass loss in high resolution biological microanalysis.

Electron beam induced loss of mass from the organic matrix and from higher Z constituents of biological samples was measured by monitoring bremsstrahlung and peak changes in EDS spectra. When any effects of contamination, extraneous X-rays, beam current drift, specimen drift, and specimen shrinkage were monitored and corrected for, the three types of samples gave consistent and similar results at 296 K. Bremsstrahlung losses averaged 45%, 46% and 50% respectively for muscle homogenate, salivary gland sections and albumin. Sulphur losses average 74%, 72% and 86% for the same three sample types. No other elements suffered significant losses. D1/e for bremsstrahlung averaged 0.14 C/cm2. Bremsstrahlung loss at 93 K began approximately one order of magnitude higher in dose, and the extent of loss varied. Sulphur losses, however, were greatly reduced at low temperatures.