There are a few ways to sample liquids that contain dissolved gases, but both involve some level of plumbing to ensure samples are caught correctly. One method is to have a valve running from the sample collection point to a "flow through" sample cylinder (a steel cylinder, sometimes lined with Teflon for inertness) that routes back to your tank or sampling point (does not disturb tank or reactor pressure). For GC analysis (the best way to quantify the dissolved gases), you will also need to plumb to the inlet with an HPLC like sampling valve and Teflon tubing. Swage-lok fittings are typically used as connectors. Samples can also be caught in something called a Welker cylinder that maintains a constant pressure on the sample. With that cold of a temperature, you will also need to make sure that the pressure increase upon warming to room temperature will not exceed the rupture disk on the edge of the sample cylinder. I am not aware of any insulating devices on the sample cylinders. Restek and Parker sell sample cylinders.
Almost forgot that you might be a student. In that case, Agilent or Hamilton sell "gas-tight" syringes that hold pressure up to about 100-200 psi. Sample your mixture while cold (i.e. in a dry ice slurry or liquid N2) and then rapidly inject in the GC.