I want to measure biological nitrogen fixation activity in some legumes using acetylene reduction assay. I got an acetylene cylinder with a regulator and just wondering how to take constant gas samples each time? Thank you.
Acetylene reduction test is done by injecting Acetylene 5ml. The Acetylene is synthesized by adding calcium carbide and water in thematically sealed flask and from it Acetylene is injected. The tubes or flasks are incubated for 24,hrs.the acetylene reduced to ethylene is measured by GLC using hydrogen and oxygen gas cylinders. The meazured acetylene can also be injected from acetylene cylinder.
Thank you Dharam. I am wondering how to transfer the acetylene from the cylinder and take known amount of acetyline using a syringer?
I can suggest a couple of devices:
1. Use a gas-tight syringe with shut-off valve (you choose the size/volume). This syringe typically has a teflon tip plunger that allows gas sampling without leakage and also has a on-off valve that keeps the gas contained, so you can deliver it when needed. You can google for "Gas-Tight Syringes with Shut-off Valves" .
Also, you will need a two-stage regulator in your acetylene cylinder and a gas plastic bag or container to allow acetylene to fill in and from which you will take the gas sample.
2. This one is more complex, but better for automation. Use a 6-Port injection valve with a loop that you can change the volume capacity. So, you fill up the loop with acetylene (in "load" position) and later delivery it (in "Inject") by flushing with an inert gas (N2 or He) at a given flow rate.
Google for 6-port injection valve and check for their operation. You can use either SS or PTFE tubing (1/16"" or 1/8").
Hi Malinda,
Attach a rubber hose to the outlet of the gas regulator. Usually a 30 - 50 cm hose is enough. Clamp the end of the hose to avoid excessive gas leaking. The hose should be soft enough to allow easy perforation using an insulin syringe for example. Open the valve, put some pressure using the pressure regulator (just until you start to see that the pressure indicator moved a little bit). When you add pressure, the attached hose will be filled with gas. Using one syringe of appropriate volume, punch the hose and collect the gas. Usually 10 % acetylene is added to the assay flask.
I hope it helps.
Cheers
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