DSC Q Series Getting Started Guide
50
Enthalpy (Cell) Constant Calibration
This calibration is based on a run in which a standard metal (
e.g
., indium) is heated through its melting transition.
The calculated heat of fusion is compared to the theoretical value. The cell constant is the ratio between these
two values. The onset slope, or thermal resistance, is a measure of the suppression of temperature rise that occurs
in a melting sample in relation to the thermocouple. Theoretically, a standard sample should melt at a constant
temperature. As it melts and draws more heat, a temperature difference develops between the sample and the
sample thermocouple. The thermal resistance between these two points is calculated as the onset slope of the
heat flow versus temperature curve on the front of the melting peak. The onset value is used for kinetic and
purity calculations to correct for this thermal resistance.
Temperature Calibration
Temperature calibration is based on a run in which a temperature standard (e.g., indium) is heated through its
melting transition. The extrapolated onset of the recorded melting point of this standard is compared to the
known melting point, and the difference is calculated for temperature calibration. The same file used for the cell
constant calibration can be used for this calibration.
In addition, you can use up to four other standards to calibrate temperature. If you use three or more standards,
the temperature is corrected by a cubic spline fit. The multiple-point temperature calibration is more accurate
than the one-point calibration if absolute temperature measurements are required over a broad (>300°C)
temperature range.
If multipoint temperature calibration is used, it is recommended that you choose standards that will bracket the
desired measurement temperature range. This will ensure optimal calibration and performance.
Heat Capacity (Q2000/Q1000) Calibration
Heat capacity can be obtained in a single experiment with the DSC Q2000/Q1000. Heat capacity calibration is
required if it is desirable to measure the absolute value of the sample’s heat capacity. The calibration uses a
standard material (such as sapphire) with a known heat capacity at a specific temperature of interest. Before
performing the calibration experiment, the previously used heat capacity calibration values need to be manually
set to the default value of 1.0. Calibration is typically done at a heating or cooling rate of 10 to 20 °C/min. Since
this calibration (measurement) uses the absolute value of the heat flow signal (Cp = Heat Flow Rate/Heating
Rate) to calculate the sample’s heat capacity, the first segment of the method should be a “Zero Heat Flow”
segment at a temperature in the middle of the temperature range for the experiment. This ensures that any drift
in the heat flow signal, since the last calibration, is corrected.
At the end of the experiment the heat capacity calibration constant is calculated by dividing the theoretical value
of heat capacity by the measured value at a specific temperature. The calculated constant is then manually
entered into the instrument control software, where it is automatically applied to future experiments.
Heat Capacity (MDSC
®
) Calibration
MDSC heat capacity calibration is only required if it is desirable to measure the absolute value of the sample’s
heat capacity or when using periods less than or equal to 40 seconds. The calibration uses a standard material
(such as sapphire) with a known heat capacity at a specific temperature of interest. Before performing the
calibration experiment, the previously used calibration value needs to be manually set for both Heat Capacity
and Reversing Heat Capacity to the default values of 1.0. Except for heating rate, the calibration experiment
should be run under similar conditions (pan type, modulation amplitude, and period) to those that will be used
