Standardization of tritium-sensitive film for quantitative autoradiography

A method for the calibration of plastic tritium standards for use with LKB Ultrofilm is described and validated. This method uses 12-microns cryostat slices of frozen liver which have been labeled with [3H]-formaldehyde and extracted with chloroform-methanol to remove lipids. Quantitative autoradiographic measurement of 3H radioactivity in the liver slices was underestimated by 35% when lipids were not extracted. Plastic sections impregnated with tritium were calibrated in terms of lipid-extracted, tissue-equivalent radioactivity content. Calibrated standard curves for these plastic standards were closely fit (p = 0.99) by second order polynomial equations for exposures of 1, 4, 7, 13, 28, and 104 days. The equations are generally useful for any plastic tritium standards.