Calibrating the DSC Enthalpy (Cell Constant) and Temperature

Calibrating Enthalpy (Cell Constant)

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 heating rate. 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.

The temperature calibration data from this experiment is automatically stored when the cell constant calibration results are saved.

DSC Q2000, Q1000, Q200, and Q100 enthalpy calibration must be performed again after a Tzero calibration and any time the heat flow selection is changed.

Calibrating Temperature

Temperature calibration is based on a run in which a temperature standard (e.g., indium) is heated through its melting transition using the same conditions to be used in subsequent measures (e.g., heating rate and purge gas). The recorded melting point of this standard is compared to the known melting point and the difference is calculated for temperature calibration. Up to five standards may be used for temperature calibration. A single-point calibration shifts the sample temperature by a constant amount. A two- or more-point calibration shifts the temperature by a constant amount below the first point, uses a smooth curve through the calibration points and shifts by a constant amount after the last point.

During cell constant calibration, the temperature calibration data from the cell constant calibration experiment is automatically stored when the cell constant calibration results are saved.

NOTE: A multiple-point calibration is more accurate than a one-point calibration. A single-point calibration shifts the sample temperature by a constant amount. A two- or more-point calibration shifts the temperature by a constant amount below the first point, uses a smooth curve through the calibration points and maintains a constant temperature shift after the last point.

Basic Instructions

Follow these basic instructions for Enthalpy/Temperature calibration or verification. Click the links to jump to the specific instructions for that item or scroll down to read the entire procedure.

  1. Perform the experiment(s), which involves choosing one or more standards and running the experiments. You can do this one of several ways:

  2. Analyze the data. You can do this one of several ways:

  3. Choose from optional Platinum functions:

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(1)  Perform the Enthalpy/Temperature Experiment

Perform the experiment(s), which involves choosing one or more standards and running the experiments. You can do this one of two ways:

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Manually Performing Enthalpy (Cell Constant) and Temperature Experiment(s) (Using the Templates)

You can perform the calibration experiments manually by following the directions below for either the enthalpy calibration or temperature calibration.

Click on the following topics for more information:

Enthalpy (Cell Constant) Experiments

A general procedure for enthalpy constant calibration is given below:

  1. Choose an appropriate calibration material with a known heat (e.g., indium).  

  2. Prepare approximately 1 to 5 mg of the calibration material in a sample pan. Crimp the pan, then position it on the sample platform.  

  3. Prepare a reference pan using the same pan type used for the sample. Crimp the pan, then position it on the reference platform.  

  4. Cover the cell.

  5. Check that your purge gas is connected and set to the desired flow rate. If you are using an RCS or LNCS, be sure a Base purge gas is also used.

  6. Select Experiment View and access the Summary Page, then set the instrument to calibration mode using the Mode Selection drop-down list.

  7. Choose the "Calibration" Mode.

  8. Select the "Cell Constant" test from the Test list.    

  9. Select the calibration material from the Sample Name list. Click on the button and verify the calibration information for this standard.

  10. Enter the requested sample information, including the exact Sample Size and Pan Type.

  11. For  Autosamplers only: Select the Pan number and Reference number.

  12. Click on the Procedure tab. Enter the requested test parameters that will program the DSC to:  

  1. Equilibrate to a temperature below the onset of the literature melting temperature of the material. Use the following equation to determine that temperature:

5 min. X Heating Rate (C/min) = Temperature (C)

Typical example: 5 min X 20C/min = 100C (below the onset of the literature melting temperature)

  1. Heat the material, at the same heating rate that you will use in your subsequent experiments, to 50C above the literature melting temperature.

  2. If you are using this standard for the first time, check the Premelt option to melt the sample before starting the experiment.

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  1. Click on the Notes tab. Enter/verify the requested information. Set the desired flow rate.

  2. Click on the Apply button to save the experimental and sample parameters entered for this run.

  3. If you wish to run multiple standards, select Append or click to add another run to the sequence.

  4. Repeat steps 1 through 12 for each calibration standard.

NOTE: If you want to have the analysis of the data performed automatically using Post Run Actions, skip to Automatic Analysis Using Post Run Actions now. Otherwise, continue with the next step.

  1. If more than one run is in the sequence list, schedule the first run in the sequence. (An arrow will appear next to the run number in the Sequence Pane for the scheduled run.) See Starting a Run and/or Sequence for more information.

  2. Select Start to begin the calibration run.

  3. Analyze the data as directed in the next section.

  4. Save the calibration sequence for future recall, if desired. Click on the Save button, , at the top of the sequence pane.

  5. Verify this result by viewing the Cell/Temperature Table window (selected from the Calibrate menu). See Viewing Cell Calibration Parameters.

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Temperature Calibration Experiments

A general procedure for temperature calibration is given below:

  1. Choose an appropriate calibration material with a known melting point.  

  2. Prepare approximately 1 to 5 mg of the calibration material in a sample pan. Crimp the pan, then position it on the sample platform.  

  3. Prepare a reference pan using the same pan type used for the sample. Crimp the pan, then position it on the reference platform.  

  4. Cover the cell.

  5. Check that your purge gas is connected and set to the desired flow rate. If you are using an RCS or LNCS, be sure a Base purge gas is also used.

  6. Select Experiment View and access the Summary Page, then set the instrument to calibration mode using the Mode Selection drop-down list.

  7. Choose the "Calibration" Mode.

  8. Select the "Temperature" test from the Test list.  

  9. Select the calibration material from the Sample Name list. Click on the button and verify the calibration information for this standard.

  10. Enter the requested sample information, including the exact Sample Size and Pan Type.

  11. For  Autosamplers only: Select the Pan number and Reference number.

  12. Click on the Procedure tab. Enter the requested test parameters that will program the DSC to:  

  1. Equilibrate to a temperature below the onset of the literature melting temperature of the material. Use the following equation to determine that temperature:

5 min. X Heating Rate (C/min) = Temperature (C)

Typical example: 5 min X 20C/min = 100C (below the onset of the literature melting temperature)

  1. Heat the material, at the same heating rate that you will use in your subsequent experiments, to 50C above the literature melting temperature.

  2. If you are using this standard for the first time, check the Premelt option to melt the sample before starting the experiment.

  1. Click on the Notes tab. Enter/verify the requested information. Set the desired flow rate.

  2. Click on the Apply button to save the experimental and sample parameters entered for this run.

  3. If you wish to run multiple standards, select Append or click to add another run to the sequence.

  4. Repeat steps 1 through 12 for each temperature calibration standard. Up to five temperature calibration standards may be used.

NOTE: If you want to have the analysis of the data performed automatically using Post Run Actions, skip to Automatic Analysis Using Post Run Actions now. Otherwise, continue with the next step.

  1. If more than one run is in the sequence list, schedule the first run in the sequence. (An arrow will appear next to the run number in the Sequence Pane for the scheduled run.) See Starting a Run and/or Sequence for more information.

  2. Select Start to begin the calibration run.

  3. Analyze the data as directed in the next section.

  4. Save the calibration sequence for future recall, if desired. Click on the Save button, , at the top of the sequence pane.

  5. Verify this result by viewing the Cell/Temperature Table window (selected from the Calibrate menu). See Viewing Cell Calibration Parameters.

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(2) Analyze the Data

Once the calibration run is complete, you can analyze the data using one of the following techniques:

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Manual Analysis

  1. Select Calibrate/Analysis from the main menu. (See Analyzing DSC Calibration Data for more detailed information.)

  2. Choose the standard that was used for your experiments. Make sure that you verify the theoretical temperature used for each standard. Edit the data if necessary. (Click here for more information on choosing/editing standards Setting Up Calibration Standards.)

  3. Select the calibration file obtained above.

  4. Once the plot is displayed, click on the Analyze button (or choose Analyze from the pop-up menu).

  5. Position the cursors to bracket the melting transition.

  6. Save the analysis. Right click on the curve and select the Accept Results function. The values will be automatically entered in the Calibration table when the analysis has been saved. To view or print the calibration results, see the Calibration report.

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Automatic Analysis Using Post Run Actions

NOTE:  These functions are available for Q2000/Q200/Q20 instruments only.

This method utilizes Post Run Actions to automatically analyze and send the results to the instrument. These are defined while setting up the run sequence and executed at the end of each test.

  1. Set up the calibration run sequence manually as described above.

  2. Right click on the temperature calibration run number on the Sequence Pane to display the pop-up menu. Select Post Run Action.

  3. Select one of the following:

  4. Select OK when finished.

  5. Repeat steps 1 through 3 for each temperature calibration standard used.

  6. Select Start to begin the calibration run.  To view or print the baseline calibration results, see the Calibration report.

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Entering Temperature Calibration Data

Select Calibrate/Temperature Table to access the Temperature Calibration Table, which is used to input or reset temperature calibration data.

This window shows the temperature calibration table that the instrument applies to the collected data. Use this window to enter from one to five temperature calibration points (pairs of observed and correct temperature points). The observed and correct temperature corresponds to the experimental and theoretical transition temperature (e.g., melting point) of the calibrant respectively.

Data is automatically entered into this table when you select Accept Results through the Calibration Analysis function (described above), using the Post Run Actions, or when using the Platinum Setup for Enthalpy/Temperature Calibration.

NOTE: A multiple-point calibration is more accurate than a one-point calibration. A single-point calibration shifts the sample temperature by a constant amount. A two- or more-point calibration shifts the temperature by a constant amount below the first point, uses a smooth curve through the calibration points and maintains a constant temperature shift after the last point.

 If these values are correct, select OK.

 If new values are to be entered follow these steps:

  1. Select the Reset button to remove all previously stored values.

  2. Determine the curie temperature points.

  3. Enter the Observed and Correct temperature points in the table.

  4. Select Apply when all points have been entered to save the settings to the instrument.

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