Getting to the Chamber
Once you have the samples from the freezer room, go into the monkey lab. Your objective is to get to the cryogenic chamber to mix the samples. Jump down from the upper floor of the lab and go through the sliding door. Head straight for the shadows to avoid the camera. Kill the soldier that passes, and have your partner disable the camera with an Optically Channelled Potentiator (OCP). Run to the cryogenic chamber and use your OCP on the same camera so your partner can join you undetected.
Mixing the Samples
It's time to split up. Enter the "A" chamber as your partner goes into the "B" chamber. Press the "Use Cryo" button and vials A, B, and C will appear in your chamber. Your partner will have vials D, E and F. Your notes will tell you which vials to mix together. This is the only way to attain this information, as the mixture changes each time you play the level. You must go first, and then your partner should immediately follow. Repeat this pattern until you are told the vials are mixed properly.
Going Up
Make a noise outside the chamber so that the guard comes to investigate. Take him out when he arrives. Have your partner disable the camera with an OCP. Press the button labeled "Call Elevator." Both of you need to get in when the door opens. Shoot the light inside and then head up. The soldier at the top will be suspicious when he realizes the elevator light is out, but at least he hasn't seen you or your partner. Take this soldier out when he gets close, and leave his body in the elevator.
Acquiring the Vial
Go through the door opposite the elevator. Grab a guard each and force them to use the retinal scanners on the wall; knock them out when this is done. Leave your partner here as you go through the open door. Peek around the corner with your back to the wall and you will see a guard. Take him down when he turns away from you. Go through the next door and shoot the spotlight. Your partner can join you now. Walk onto the metal grate and choose the option "Init Hangover." Lower your partner into the cryogenic chamber to grab the vial.