On calculating concentrations of “HCO3” from pH and PCO2

Burton, R.F. (1987) On calculating concentrations of “HCO3” from pH and PCO2. Comparative Biochemistry and Physiology Part A: Physiology, 87(2), pp. 417-422. (doi:10.1016/0300-9629(87)90145-9) (PMID:2886282)

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Abstract

1. As used in the Henderson-Hasselbalch equation, [HCO3], [CO2] and pH may all be variously defined; values of pK'1 must be chosen accorclingly. 2. In common usage, “HCO3” may include CO3, carbamate, various ion pairs and possibly other bound CO2, as well as free HCO3 ions. 3. pH measurements may be systematically affected by the choice of standard buffers and by proteins and blood cells, and the errors in pH may be pH-dependent. 4. Accorcling to how it is expressed, the solubility coefficient for CO2 (S) may be influenced by sample water content, proteins and lipids. However, it need not feature in the calculation. 5. pK'1 is often found to decrease with increasing pH. This may be partly due to inclusion of CO3 and carbamate, but not of H2CO3.HCO3−, in “HCO3” and partly, perhaps, to errors in pH measurement. 6. To the extent that pH measurements are reliable, concentrations or activities of true HCO3 are calculable from pH and PCO2, but, if pH measurements are likely to be systematically erroneous, it may be preferable to define “HCO3” as “total bound CO2” and to base pK'1 on gasometric or titrimetric determinations of that.

Item Type:Articles
Status:Published
Refereed:Yes
Glasgow Author(s) Enlighten ID:Burton, Dr Richard
Authors: Burton, R.F.
College/School:College of Medical Veterinary and Life Sciences > School of Life Sciences
Journal Name:Comparative Biochemistry and Physiology Part A: Physiology
Publisher:Pergamon Press
ISSN:0300-9629

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