Permeation source concentration calculator

This attached calculator spreadsheet allows you to determine the concentration of an analyte gas from an OVG in the flow path up to and including the detector being used.

The equation to calculate the concentration (Cell C10) is as follows:

concentration (ppb) = 1000 x Gas Constant x perm rate (ng/min) /  ((V-OVG Sample + Exhaust Flow) x Mol Wt) 

Note: on the spreadsheet you can edit the yellow cells only.

The default gas constant value is set for a lab with air conditioning set to 20°C and under Normal Temperature and Pressure conditions.

Should you use additional mass flow controllers to add makeup flows or to dilute the flow further, these can be calculated using the other yellow cells.

To use the calculator:

  • Enter the analyte permeation rate in Cell B2, and the analyte molecular weight in Cell B3.
  • Enter the required flow for your detector in Cell S11.
  • To obtain the greatest dynamic range from the vapour generators, set the Sample flow in Cell B4 to the lowest flow possible for your equipment (25mL/min for the V-OVG, 50mL/min for the OVG-4).
  • If your Sample Flow (plus OHG or other Makeup Flow entered in Cell F3) is less than your detector flow (Cell S11), the calculator will indicate the required makeup Flow in Cell N3
  • To achieve the highest concentration possible from the vapour generators, set the Exhaust/Split Flow to 0mL/min.
  • This gives you a concentration of your analyte in ppb in cell C11
  • To adjust the concentration at your detector, adjust the Exhaust/Split Flow in Cell B5.
  • If you wish to use mg/m3, then you can find several online conversion calculators for this.


Using Benzene as an example for maximum dynamic concentration range:

  • Analyte permeation rate= 6792 
  • Analyte molecular weight = 78.11
  • Sample flow to 25mL/min

To get the highest concentration set:

  • Exhaust Flow to 0mL/min

then this gives you a concentration of 83476.12ppb (83.476ppm).

And to get the lowest concentration:

  • Exhaust Flow to 3000mL/min

then this gives you a concentration of 689.89 ppb



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