[Criteria for the use of the linear allothermal short-time test in predicting stability (author's transl)]

Three selected model substances of varying activation energy (naphazoline, 109 kJ/mole; acetylsalicylic acid, 72 kJ/mole; and phenobarbital, 60 kJ/mole) were studied to determine the conditions under which the allothermal short-time test according to Zoglio (linear increase in temperature) will yield stability predictions which are consistent with those provided by the isothermal short- or long-time test. The error of the determination method should be less than or equal to 1%. It is advantageous to use for the calculation as many data as the analytical facilities will permit to obtain. The actual value for the respective temperature should differ from the desired value by < +/- 0.2%. The increase in temperature should be very slow 1-2 degrees C/h at best). This is particularly true for substances of low activation energy, because more the energy values calculated on the basis of the allothermal test differ from the isothermally determined values, the flatter is the curve provided by the arrhenius equation. The temperature range should be chosen as large as possible, from 30-90 degress C, and the experiment should be continued until at least a 10% decomposition is achieved. On calculating the collision factor A and the reaction-rate constant for any temperature, it has proved useful to continue the experiment isothermally at the final point of the allothermal test.