A new reference method for the determination of the total CO2 concentration in biological fluids

It appeared that a part of a measuring system recently developed for the determination of the oxygen content of blood (Dijkhuizen, P., Kwant, G. and Zijlstra, W.G. (1976) Clin. Chim. Acta 68, 79), was perfectly suitable for measuring the total CO2 content of blood, plasma or other fluids. CO2-free room air is pumped through an extraction vessel in which all the CO2 of the sample is set free by an acid reagent, and swept by the carrier gas to a titration vessel containing a BaCl2 solution. CO2 is bound as BaCO3 and the ensuing H+ titrated with an NaOH solution. The method was tested by measuring a series of Na2CO3 reference solutions. The values measured by titration amounted to 99.4 +/- 0.8% of the concentration of the reference solutions (range 10--50 mmol 1(-1). The coefficient of variation was 1.8% for 5 mmol 1(-1) solutions and 0.2% for 50 mmol 1(-1) solutions. In measuring a series of 60 blood samples the coefficient of variation as calculated from duplicate determinations was 1%.