Best to stick with standards for research and medical type studies, or report what was used if not.  I found this if you are not aware of difference between two grades, and unsure if food grade is medical grade.

• The slight difference between industrial-grade CO2 and food-grade CO2 is the type of tests that are done to qualify CO2 as beverage or beer gas-grade compared to industrial-grade. Currently, the FDA's requirement for food-grade CO2 a 99.90% purity rating. The other .09% is made up of impurities such as hydrocarbons or nitrogen. Industrial grade CO2 is 99% pure CO2, also containing impurities such as hydrocarbons or nitrogen.

Apparently impurities such as benzene can be a big deal for some applications, such as making beer that can leave beer drinkers with headaches.

Thank you so much. You have been very helpful.

If your assay may be sensitive to trace gases such as ethylene there are solid phase scrubbing sysytens invilving KMnO4.  I'm sure there are techniques to scrub other common contaminants.