Analysis Conditions

  In 21CFR11 environments, this section is applicable only to members of the Developer group, however, members of the Analyst group may find information in this section helpful. Parameter file information that is available to Analysts is created by a member in the Developer group using information in this section.

(or click the Analysis Conditions tab when in Advanced option presentation)

Analysis conditions specify the parameters used to guide an analysis.

Analysis Conditions
Field or Button Description
Absolute pressure dosing [check box] Specifies pressure targets in mmHg, mbar, or kPa instead of relative pressure. If this option is selected, the Relative Pressure labels and entries change to Absolute Pressure in the selected pressure units. This option is typically selected when using adsorptives at analysis conditions above the critical point of the gas; for example, H2 adsorption on carbon at liquid nitrogen temperature.
Adsorptive
[drop‑down box]
Select an Adsorptive Properties file from the list of defined gases to be used for analysis. After selection, click Edit to modify adsorptive properties. See Adsorptive Properties.

Analysis Conditions
[drop‑down box]
Use to browse for an Analysis Conditions file that contains analysis condition parameters to be used in the analysis.
Backfill [button] Select gas for backfilling the sample tube at the start and end of an analysis.

The options are disabled if the file status is Entered, Complete, or Analyzing.
Dose Increments
[selection]

The sample is dosed repeatedly with a fixed amount of gas and isotherm points are collected after equilibrating each dose.

Options [button]. Each entry in the table defines how much to dose for a segment of the isotherm. In this form of dosing, there is no predefined pressure table. Define target ranges for up to 10 dose increments. The ending relative pressure and the dose amount (entered or as the fraction of the previous quantity adsorbed) for each target range are shown.

Equilibration [button]

Provides options to specify the equilibration interval and delay time.

Minimum equilibration delay at p/po > = 0.995.  The minimum number of seconds required before equilibration can occur for a relative pressure greater than or equal to 0.995. This field is not available if Absolute pressure dosing is selected on the Analysis Conditions tab.

Relative Pressure (p/po) or Absolute Pressure. The pressure the equilibration interval will be applied.

Free Space [button]

Use to enter the free space measurement type.

Measure:

  • Lower dewar for evacuation. If the dewar is to be lowered for evacuation, select this option and enter the length of time for evacuation after the free space measurement in the Evacuation time field. If using a cryostat, the operator must manually move the cryostat assembly when prompted.
  • Evacuation time. The length of evacuation time prior to free space measurement.
  • Outgas test. Checks for system leaks or sample outgassing. After free space is measured, the dewar is lowered and the sample evacuated for the specified amount of time. The leak test is performed after evacuation. If the pressure rises more than 0.025 mmHg within the time specified in the Outgas test duration field, outgassing is present. If a leak is found, the leak test repeats nine times, with 30 minutes evacuation between tests. If the 10th leak check fails, the analysis stops and the operator is notified. While leak testing slightly increases analysis time, it prevents the continuation of analysis and collection of erroneous data if a leak occurs.

Enter. Measures free space after analysis ends. Enter the estimated free space measurements.

  • Ambient free space. Empty sample tube gas capacity measured at room temperature.
  • Analysis free space. Empty sample tube gas capacity measured with the dewar raised.

Calculate. Use to have the free space measurement calculated using the sample and tube parameters.

Options [button] Available when the Target Pressures option is selected.

First Pressure Fixed Dose.

This option is most frequently used when performing a standard nitrogen analysis of mesoporous materials such as catalysts. If the first pressure table point is low and the gas uptake of the sample is expected to be high, this option can shorten the time required to reach the first point on the pressure table.

The sample is dosed repeatedly at low pressures with a specified amount of gas until the first pressure point is reached. This initial dosing quickly meets the adsorptive demand of the sample.

The first point on the pressure table is the threshold value. Once this first pressure point is reached, points are equilibrated and recorded in accordance with the specified pressure table.

Enter the amount of gas to be added to the sample for each dose cycle.

Maximum volume increment.

Select to determine when additional data points are collected between target pressures in regions of adsorption. When the maximum increment has been adsorbed since the last collected data point, another point is equilibrated and collected. During desorption, this field is treated as a maximum volume decrement value.

When using this option, reaching pressure points exactly is not important; therefore, the tolerances should be set relatively large (10 mmHg and 10% or so) for proper functioning of the algorithm. The pressure table should also have several points scattered over the region of interest.

This field is disabled if First pressure fixed dose is selected.

Absolute / Relative pressure tolerance.

Values used to determine how close the actual pressure must be to each target pressure from the pressure table. At lower pressures, the relative tolerance value is lower. At higher pressures, the absolute tolerance value is lower.

Experiment 1. There might be an absolute tolerance of 5 mmHg, a relative tolerance of 5%, and a target pressure of 40 mmHg; 5% of 40 mmHg is 2 mmHg. Since 2 mmHg (relative tolerance) is lower than 5 mmHg (absolute tolerance), 2 mmHg is used. Therefore a minimum pressure of 38 mmHg (40 - 2) must be attained to collect data for a target pressure of 40 mmHg.

Experiment 2. There might be an absolute tolerance of 5 mmHg, a relative tolerance of 5%, and a target pressure of 200 mmHg; 5% of 200 mmHg is 10 mmHg. Since 5 mmHg (absolute tolerance) is lower than 10 mmHg (relative tolerance), 5 mmHg is used. Therefore a minimum pressure of 195 mmHg (200 - 5) must be attained to collect data for a target pressure of 200 mmHg.

Normally, surface area measurement points are widely spaced and the resulting measurement is not very sensitive to the precise location of points so wider tolerances may be used. Unnecessarily tight tolerances lengthen the analysis.

Low Pressure incremental dose mode.

Select when performing an analysis of microporous materials. At low pressures on Type 1 isotherms, the pressure points are very closely spaced, making a useful pressure table difficult to define. When enabled, equilibrium points are measured at approximately equal intervals on the quantity adsorbed axis. Each dose is fully equilibrated and recorded as a data point.

In this mode, the sample is successively dosed with a specified amount of gas until the first pressure point is reached. The first point is the threshold value, triggering the transition from Incremental Dose Mode to Pressure Table Mode. When the first pressure table value is reached, Incremental Dose Mode is disabled, and points are recorded in accordance with the specified pressure table. Because the data points recorded during Incremental Dose Mode may define most of the analysis, one point on the pressure table can be sufficient and serve as the end point for the analysis.

  • Dose amount. The amount of gas to be added to the sample for each data point until the first point on the pressure table is reached. This field is enabled when Low pressure incremental dose mode is selected.
  • Equilibration Delay. Enabled when Low Pressure incremental dose mode is selected.

Minimum. Prevents premature equilibration caused by reduced percentage sensitivity to pressure changes at the lowest pressures.

Maximum. Prevents the effects of long term temperature or pressure drift, which may cause the analyzer to wait an excessive length of time for equilibration.


p° and T [button]

Click to select one option for obtaining the saturation pressure (Po) and analysis bath temperature. Each selected option presents a different set of parameters at the bottom of the window.

Options and descriptions:

  1. Analysis bath temperature (not used for krypton analyses). Measures the p0 on a continuous basis. Allows the measurement of each data point without slowing the analysis.
  2. Analysis bath temperature (not used for krypton analyses). Measures the p0 on a continuous basis and over the sample, then adjusts the measured p0 in the sample tube to agree with the p0 over the sample.
  3. The p0 and analysis bath temperatures or an analysis bath temperature only (when Absolute pressure dosing is selected on the Analysis Conditions window). This method uses the entered values.
  4. Psat gas. If this is a krypton analysis, select the Nitrogen @ 77.35K option from the Adsorptive drop-down box. Click Psat vs T to edit the values of the Psat vs T table. Editing the values in the current table does not affect the original table.
  5. Analysis bath temperature. Analysis bath temperature and an estimate for the initial p0 (not used for krypton analyses). Measures the p0 over the sample. After the p0 is measured, the value is reapplied to all data points.
  6. Analysis bath temperature. This method calculates the p0 at the time of analysis using the entered temperature.
If From last sample tube (for krypton analysis) on the analysis window and a p0 option other than 3, 4, or 6 is selected, an error message is displayed when the analysis begins.
Preparation [button] Use to enter analysis preparation details.

Evacuation rate. The rate for restricted evacuation.

Evacuation time. The length of time for preliminary evacuation which takes place prior to the free space measurement or sample analysis if free space is to be entered or calculated.

Fast Evacuation. Select for samples (such as pellets) that do not fluidize or shed particles during evacuation.

Leak Test. Enables the system to check for leaks or sample outgassing before the analysis. The leak test allows sample pressure to rise during the test. If the pressure rises more than 0.15 mmHg, the analysis does not proceed and the operator is notified. While leak testing slightly increases analysis time, it prevents the continuation of analysis and collection of erroneous data if a leak exists. Select to enable the Leak test duration field.

Leak test duration. Enter the duration of the leak test.

Unrestricted evac. from. The pressure at which unrestricted evacuation is to begin. This option is enabled when Fast evacuation is not selected.

Use TranSeal. Select if using the TranSeal to transfer the sample from the preparation port to the analysis port under vacuum.

Pressures [button]

Available when the Target Pressures option is selected. Use to edit the Entered Pressures table.

The pressure table consists of relative pressure points at which isotherm data are to be collected. An optional pressure increment can be entered in the Pressure Increment column, which will cause additional points to be collected at intervals of the pressure increments up to the relative pressure specified in the Ending Pressure column.

The relative pressure points may span the entire range of 0.000000000 to 0.000000001 p/p0. There must be one adsorption branch (strictly increasing pressures) followed optionally by one desorption branch (strictly decreasing pressures).

  For fields and buttons not listed in this table, see Common Fields and Buttons.
 
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