Premium
Considerations for osmolality measurement under elevated p CO 2 : Comparison of vapor pressure and freezing point osmometry
Author(s) -
Schmelzer Albert E.,
deZengotita Vivian M.,
Miller William M.
Publication year - 2000
Publication title -
biotechnology and bioengineering
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.136
H-Index - 189
eISSN - 1097-0290
pISSN - 0006-3592
DOI - 10.1002/(sici)1097-0290(20000120)67:2<189::aid-bit8>3.0.co;2-u
Subject(s) - osmometer , freezing point depression , chemistry , vapor pressure osmometry , freezing point , osmotic pressure , bicarbonate , mannitol , chromatography , vapor pressure , analytical chemistry (journal) , biochemistry , thermodynamics , organic chemistry , physics
Osmolality increases with p CO 2 in bioreactors with pH control, and it has been shown that osmolality compensation by decreasing the basal NaCl concentration partially mitigates the adverse effects of elevated p CO 2 on animal cell growth, protein production, and glycosylation. Thus, measurement of osmolality is important for a complete characterization of the culture environment under elevated p CO 2 . However, osmolality measurement may be compromised by CO 2 evolution. Freezing point depression and vapor pressure depression osmometry were directly compared for the measurement of osmolality in samples at elevated p CO 2 (up to 250 mmHg) and at a variety of pH values (6.7–7.5). More extensive degassing may be expected with the vapor pressure osmometer due to the smaller sample volume and larger surface area employed. However, both types of osmometer yielded similar results for all p CO 2 and pH values studied. Moreover, the measured values agreed with osmolality values calculated using a semi‐empirical model. Further analysis showed that, while sample degassing may result in a large decrease in p CO 2 , there is little associated decrease in osmolality. The great majority of total CO 2 in solution is present as bicarbonate (HCO 3 − ). Although a small amount of HCO 3 − is converted to CO 2 to compensate for CO 2 evolution, further depletion of HCO 3 − is inhibited by the associated increase in medium pH and by the need for HCO 3 − to maintain charge neutrality in solution. This explanation is consistent with the observed similarity in osmolality values for the two types of osmometer. It was also observed that osmolality did not change in samples that were frozen at −20°C for up to 1 year. © 2000 John Wiley & Sons, Inc. Biotechnol Bioeng 67: 189–196, 2000.