Electron irradiation effects in the EPMA quantitation of organic specimens.

Electron irradiation of organic specimens adversely affects the validity and reliability of quantitative microanalytical results through the loss of light element constituents of the specimen. Characteristic and continuum x-ray count rates will vary for the duration of the irradiation effects, which require electron doses of 10(-11) to 10(-8) C/micrometer 2. The magnitude of these variations is dependent upon the light element content, thickness and temperature of the specimen and upon the operating conditions used during analysis. The initial count rate at the onset of the electron beam is the most valid count rate to be used in the quantitation of organic specimens, but it can only be accurately determined when the analyzed element exists in high concentration within the specimen or when the beam is grossly defocused. Low temperature analysis will prolong the duration of the mass loss and decrease its magnitude, but erratic count rates, specimen charging due to condensation and inconsistent mass losses have been observed for different specimens. The physics and chemistry of the electron beam-specimen interactions impose limitations upon the potential accuracy in biological microanalysis whic, if ignored, can result in large errors in quantitative projections.