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 concentrate the concentration is as follows:
conc (ppm) = perm rate (ng/min) / (TOTAL flow through V-OVG) / Mol Wt) x Gas Constant
Note: on the spreadsheet you can edit the yellow cells only.
The dropdown in cells C/D5 are to select the appropriate gas constant value for the equation.
The default constant value is for a lab with air conditioning set to 20°C, but the other selections are for 0°C or 24°C.
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.
- If you leave C/D5 as it is (default 20°C lab temperature).
- To obtain the greatest dynamic range from the V-OVG, set the Sample flow in Cell B4 and set the Exhaust Flow in Cell B6.
- This is the highest concentration possible from the V-OVG (but you will probably need to increase the total flow to your detector (Cells S12 or F3).
- This gives you a concentration of your analyte in ppb in cell C11
- 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