I hate to be the one to tell you this but, creatine serum is crap. They have less than two grams of creatine per BOTTLE. Because Creatine stored in a liquid doesn’t stay stable and turns into creatinine which is a waste product. That is why it is also very important to keep your creatine dry. Get the powder, it actually works and it will last you alot longer.
As for the glutamine. Yes, you can mix it into your post-workout shake. In fact I encourage you to. Glutamine plays a big role in protein metabolism, and many top protein powders already contain it.
I agree that creatine serum is crap – very expensive crap. I also think you can mix glutamine with almost anything. I take glutamine 3-4 times per day(depending how hard you work out) becasue your body is recovering all day, so why just take it in one 2-hour time span? Try it and mix on!