Gas Calibration

Sample Files

Use to calibrate the TCD so that peak area data can be converted to volume data. During a gas calibration, a series of known gas mixtures flows through the analyzer and the resultant signal readings are recorded. The analyzer can then use these data to calculate the concentrations of unknown mixtures flowing past the detector during subsequent analyses.

In some cases (such as in TPR analyses), the analyzer needs to know how to correlate the signal readings collected in the analysis with the volume of gas uptake at any given point in the analysis. If the analyzer is provided with a series of known gas concentrations, and it records the signal associated with each known concentration, then it can use this information to calculate the concentrations associated with the signals it recorded during the analysis. From that point, it can also calculate the volume of gas associated with each peak in the data.

  Zeroing all Mass Flow Controllers is recommended prior to gas calibration to ensure its accuracy. Consider inserting a Zero MFCs task to the analysis conditions list. See Experiment Steps, Zero Mass Flow Controllers.
  1. Prepare and install a clean, empty sample tube.
  2. Ensure the correct gases are connected and the Adsorptive Properties file has been updated.
  3. Create the sample file:
  1. Go to File > New Sample.
  2. Complete the fields on the Sample Description tab, as needed.
  1. Select the Analysis Conditions tab.
  2. Click Insert and select Gas Calibration.
  3. Click OK.

  1. Complete the window entering the appropriate information for the sample being used.

 

Specific selections and entries shown in this table are only applicable when using Micromeritics samples. Make the necessary adjustments when using non-Micromeritics samples.
Selections Description
Blend or Loop Gas [drop‑down box] Select Hydrogen-Argon and enter 10 for the Maximum active gas concentration percentage. The concentration is listed on the Certificate of Analysis on the gas cylinder.
Carrier/Reference Gas [drop‑down box]

Select H2/Ar and enter 50 as the Reference flow rate.

Select Ar as the Blend.
Description [text box] Enter a description for this calibration.
Filament temperature [selection] Enter the temperature between 20 to 250 °C for the filament. A typical setting is 245 °C.
Set external trigger [check box] If selected, the contact closure used to trigger an external mass spectrometer will be activated. If deselected, the contact closure will be deselected.
Temperature [group box] Enter a value between 20.0 and 150.0 °C for the Valves and Detector block. A typical setting is 110 °C for the valves and 100 °C for the block.
  1. Click OK again to close the Calibration window.
  2. Click Save As, provide a new file name, then click Close.
  3. Go to Unit [n] > Sample Analysis.
  4. Click Browse to locate sample file previously created.
  5. Click Start to start the analysis. Use the other views of the analysis window to observe the progress of the analysis. During the automatic analysis, the analyzer decreases the proportion of the analysis gas in 10% increments, beginning with 100% and ending with 0%. The resultant data should appear as a series of ten stepwise changes in the TCD signal.
  1. When the analysis ends, close the Analysis window.
  2. When the displayed sample temperature reaches the ambient temperature, open the furnace and remove the sample tube.
  3. Go to Options > Signal Calibration > New. Select the calibration file, then click Open.
  4. Click Load Calibration Data then select the sample file for this calibration, then click OK.
  5. Click OK. The data in the sample file are automatically inserted into the appropriate fields of the Signal Calibration window.
  1. Assess the gas concentration plot, Goodness of Fit, and Coefficients to determine if the calibration file is acceptable. Use your laboratory’s standards to determine what level of linearity is acceptable. As a general guideline, use a calibration file with a very low value for Goodness of Fit (less than 1/2% of the maximum concentration) when 1st or 2nd Degree is specified.

Data points that deviate significantly from linear can be deleted. Evaluate the results when the degree is changed (select a different degree from the drop-down list).

  1. When satisfied with the calibration file, enter a descriptive name in the Description field.
  2. Click Save, then click Close.
  3. Go to Options > Signal Calibration > Report to select a report to generate.