Temperature and acid concentration in the search for optimum Feulgen hydrolysis conditions.

Exposure and removal of aldehyde groups during Feulgen acid hydrolysis were studied at a wide range of temperature and acid concentrations. Temperatures between 9 and 75degreesC were found to influence only the rate of the hydrolysis reaction over the entire range from high (6 M) to low (0.05 M) HCl concentrations. The temperature dependence was high, and around +5degreesC was sufficient to double the reaction rate. The influence of acid concentrations between 0.02 and 6 M was studied, and the extraction rates that determine the peak values of the Feulgen hydrolysis curve were found to depend in the same way on the (H+) concentration. A diagram is given that makes it possible to determine the time to reach the point during hydrolysis where the maximum amount of aldehyde groups are developed for a wide range of temperatures and acid concentrations. Temperatures slightly above room temperature in combination with high acid concentration is recommended for Feulgen hydrolysis.