Quantitative electron probe microanalysis of biological thin sections: the use of stem for measurement of local mass thickness.

A method for performing quantitative electron probe microanalysis on ultrathin ( 2 ) biological samples is described and evaluated. The technique is based on a measurement of the characteristic peak count rate and the degree of beam attenuation as the primary electron beam passes through the sample. Using this method it is possible to measure the concentration of a given element such as sodium in sections ranging in mass-thickness from several μg/cm 2 up to 30 μg/cm 2 with an accuracy of better than 10%. For sections having a mass thickness of approximately 11 μg/cm 2 the minimum detectable concentration for sodium was found to be 20 mmolar or 4 × 10 −2 wt.%. The interaction of the electron beam with the sample is also discussed with emphasis on characterizing the variation in sample mass with radiation dose.