Spormann Lab:Protocols:GCLowSolubilityGasStandards

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Analytical Methods: The Joerg Method of Making Gas Standards.

As recorded by Koshlan (March 4, 2014)

Making gas standards can be a bit of mystery especially when everyone in the lab has their own set of tricks. Joerg has a genius method of constructing standards for gases that are not soluble in water, which can be used repeatedly. He uses 1.2 L bottles with septum tops. By controlling the volume of water in the bottle one can keep the pressure constant even as one takes repeated samples -- simply by replacing the sampled volume of gas with the same volume of water. This doesn’t work for water soluble compounds, but is fine for methane, hydrogen, or ethylene with only a small error due to gas entering the liquid phase.

Here is the protocol to construct standards of Ethene (aka Ethylene).

A. Buy Tank of 100% Ethene from your favorite supplier.

1. Use 1.2 L bottles with gas tight tops and butyl stoppers. Larger volume bottles for standards will be more accurate and allow for more repeated samplings and are easy to construct.

2. Fill the 1L bottle completely with water so the meniscus is over the top of the bottle; Stick a needle through the stopper and place the stopper in the bottle; the water will squirt out the stopper; crimp the bottle.

3. With the needle still in the stopper, stick a nitrogen line in the bottle and all of the water will be replaced with nitrogen, flush out exactly 1L of water. Afterwards make sure there is no over pressure.

3. Fill syringe with 1ml of pure ethylene gas from standards. Remove 1ml of Water. Now your bottle contains 1/1000th pure Ethene.

4. Inject 1ml of 1:1000 ethene into the next prepared 1L bottle to make a 1:10^6

5. When you remove 300 ul of gas replace with the same volume of water.

6. There is an added bonus to having water in the bottle. You can turn it upside down letting the water block the stopper. This help prevent gas loss over time. These standards should be stored at room temperature and can be used again and again.

Ethene Example:

Assume that you have 1ml of gas at 1 atm pressure at 25C.

PV = nRT

RT/P = V/n

(0.0821 L atm/K mole)(293 K) / 1 atm = 24 L/mole

0.001L/24L = 4.16E-5 Mols Ethene in the first Vial

If you are using 0.0003L injection volumes that means the concentration of Ethene gas is 1.25E-08 Mols/L