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Conversion of parts per million (ppm) to gram/liter
Conversion of ppm (mole basis) to gram/liter for Gas Mixtures:
Example – Given a 100 ppm (mole basis) gas mixture of Compound A in nitrogen, how much of Compound A will be contained in a 1 liter volume?
Key Assumptions:
- Temperature of sample is assumed to be at 21.1°C (70°F).
- Pressure of sample is assumed to be 1 atm just before injection. At around atmospheric pressure, gases behave in close to ideal manner.
Calculation:
Using the Ideal Gas Law (PV = nRT) for a temperature of 294.1°K (21.1°C), a pressure of 1atm, and the gas constant R of 0.0821 liter x atm/mole x degree K, we find that 1 mole of ideal gas occupies 24.15 liters.
One liter of gas will then contain (1/24.15 ) moles. Since the concentration of Compound A is 100 ppm, the total number of moles of Compound A in 1 liter is ( total # moles per liter) x (concentration of Compound A).
The concentration of 100 ppm (parts per million) is unit-less, and equals 100 mole-parts per 1,000,000 total moles = 0.000100 in decimal form; thus the amount of moles of Compound A in one liter of mixture is:
(1/24.15) moles per liter x 0.000100 = 0.000004 moles of Compound A per liter
In order to find the weight of Compound A, we need to know its molecular weight. For example, if Compound A is hydrogen sulfide, with a molecular weight of 34.08 gram/mole, we obtain the following concentration:
0.000004 moles per liter x 34.08 gram per mole = 0.000140 gram per liter or 0.140 milligram per liter
General Formula for Conversion of ppm (mole) to gram/liter for Gas Mixture:
(for temperature 21.1°C (70°F) and pressure 1 atm)
{Concentration (decimal form) x mole-weight (gram/mole)} of Comp. A |  | Concentration of |
------------------------------------------------------------------------------------------------- | = | Comp. A in g/l |
24.15 liter / mole | | |
Conversion of gram/liter to ppm (mole basis) for Gas Mixture:
( for temperature 21.1°C (70°F) and pressure 1 atm)
Concentration of Comp. A in gram/liter x 24.15 liter / mole | | Concentration |
------------------------------------------------------------------------------------------------- | = | of Comp. A |
Mole-Weight of Comp. A in gram/mole | | in Decimal Form |
The concentration expressed in decimal form is unit-less. To find the concentration of Compound A in ppm, multiply the answer from equation above with 1,000,000. For example, a concentration of Compound A of 0.000100 (decimal form from equation above) would be 100 ppm, while a concentration of 0.010000 would be 10,000 ppm or 1%.
For details, see “Conversion of ppm (mole basis) to gram per liter for Gas Mix.“
Other Unit of Measure Conversions => 
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