Received May 12, 2006
Accepted September 22, 2006

Objective:To characterize the bicarbonate and HEPES buffer systems of commercially available culture media when exposed to different carbon dioxide(CO2) concentrations and incubators. Method:.The following media were analyzed:1)Asp®,Gamete®,IVF®:Vitrolife, Sweden; 2)Sperm buffer®,Follicle flushing® Oocyte wash®,Fertilization®an Cleavage®:Cook,USA; 3)modifiedHTF®:Irvine Scientific, USA.Measurements of pH were performed using a calibrated and certified pHmeter.Experiment1 analyzed pH values after overnight CO2 incubation in an open culture system model.Experiment2 assessed the time interval in which CO2-dependent media maintained pH within physiological range after ambient air exposure.Experiment3 studied the CO2 incubation period required for CO2-dependent media to stabilize at physiological pH levels after 5-minute ambient air exposure. Results:Experiment1 demonstrated an inverse relationship between increased incubator CO2 concentrations and pH levels.Exposure to CO2 must be avoided to prevent acidification in HEPES-buffered media, with exception of Sperm buffer®,Gamete®andAsp®. Experiment2 showed a time-dependent increase in the pH levels of all CO2–dependent media after ambient air exposure, which was not attenuated by incubation at increased CO2 levels. All but Gamete® and Asp® HEPES-buffered media can be air exposed for long time periods without pH destabilization.Experiment3 showed that bicarbonate and CO2–dependent HEPES-buffered media required a 45-90and 5-15-minute CO2 incubation period for pH re-equilibration after ambient air exposure. Conclusion:Characterization of commercially available culture media should be included in the in vitro fertilization laboratory quality control program.These procedures may help the embryologist to understand media behavior from distinct manufacturers at a work condition of a particular laboratory.Therefore, fine adjustments and/or protocol modifications can be made to optimize gamete and pre-embryos culture conditions.