Aero-Laser Peak Integrator

Overview

The Aero-Laser Peak Integrator was designed to determine the exact mass content of a trace gas from a concentration peak. The software post-processes data obtained, by an Aero-Laser trace gas analyzer. Sampling could be done e.g. by thermal desorption or by evaporating the gas content in an oven. For example, the Micro-Chamber µ-CTE is an ideal tool to determine the content of a formaldehyde sample of well known weight.  

The software calculates the absolute mass and volume contained in a concentration peak, including an exact background correction.  

Fig. 01: The Setup window. The column title must match to the title in the data set.

Input file format

The software can import almost any type of ASCII data organized in columns. The data format will be recognized automatically in most cases. If not, there is a Setup window for manually adjusting the data format. The import filter supports the file extensions "csv", "txt", and "dat". The column containing the time stamps should be labeled with "Time". 

The date/time format should be adjusted in SqeezeDatExport to fit one of the formats shown in Fig. 01. Fractions of seconds will be ignored.

The built-in parser requires the exact title of the column in the data set, containing the concentration data. This is also specified in the setup dialog.

Loading a data set

Data is loaded by pressing the Open Data button. The software will remember the path to the last data loaded. After reading text from .csv, .txt, or .dat files the data is parsed automatically and a graphical output is generated. If the title of the column, containing the concentration data, does not match to the title used by the software, an error message is displayed. Please open the Setup window and input the columns title.

Fig. 02: Main window showing the concentration vs. time. The borders defining the Region Of Interest (ROI) are set by clicking with the left or right mouse button, respectively. The HCHO content is calculated by integration over this region and is given as volume and mass.

The data plot can be zoomed in and out by dragging a rectangle with the mouse (left button), while the control key is pressed on the keyboard. To zoom out one level do a right click with the mouse while the control key is pressed. The zooming function has virtually infinite levels. 

 

Fig. 03: The borders of the ROI used for calculation are indicated by red markers.

Calculating volume and mass of HCHO in a peak

A Region Of Interest (ROI) is defined around the peak by clicking with the left, and right mouse buttons next to the peak (see Fig. 03). The borders of the ROI are indicated by red markers. Make sure that the marker with "R" is on the right side of that with the "L". 
The content of HCHO in the sample is calculated by pressing on the button Calc Integral. Integration is done by summing up the concentration and multiplying the result with Δt:

 

The gas flow of the instrument (in liters/min), the environmental pressure (in mbar) and the temperature (in °C) in the stripper must be set to the current values before the calculation. Flow and stripper temperature are measured by the instrument. The environmental pressure must be obtained elsewhere.
The result is given as volume in nL (10-9 liters) and mass in ng (10-9 gram). The mass is calculated from the volume using the ideal gas law. All values can be exported as an XML-file.

Base line correction

Base line correction is integrated in the calculation of the HCHO content. The base line can be either set manually by putting in the base line value in the edit box (see Fig.04) or by calculating it with the software. For this calculation, the markers should be set in an appropriate region of the plot showing the base line level (See Fig. 05). By pressing the button Calc Baseline, the software calculates the average value in the selected region and stores it. The value is also shown in the corresponding edit box. 
If the Use baseline correction box is checked, the baseline is subtracted from the data in the calculations of the HCHO content of a peak in the data. The corrected data is shown as a red line in the plot, while the original data is shown in light blue (See Fig. 06). Like all other settings, the software remembers the base line value.

  • Fig. 04: Edit control for base line correction. The base line can be set manually in the edit box or can be calculated by the software.
    Fig. 05: To calculate the baseline, set the markers in an appropriate region and press the Calc Baseline button.
  • Fig. 06: Base line corrected data in the main window (red) and original data (light blue) are shown, if the Use baseline correction box is checked.