Abstract: In a blood gas analyzer, a measurement liquid, advantageously high-purity water, is fed from a suitable vessel to a diffusion cell in which the measurement liquid is brought into contact via a diffusion membrane with the blood sample to be tested. When the gases dissolved in the sample have diffused through the membrane, the measurement liquid which has remained static in the diffusion cell is propelled into a measuring cell in which the value of an electrical quantity related to the pCO.sub.2 is determined. The measurement liquid is then fed to discharge. In a preferred embodiment, the measurement liquid is discharged into the vessel from which it has been initially withdrawn via passage through means for retaining ionic impurities.

Abstract: In a blood gas analyzer, a substantially oxygen-free measurement solution is fed through a measuring cell as far as a diffusion cell in which the measurement solution is brought into contact with a blood sample to be tested. The gases dissolved in the blood sample diffuse through a membrane in the diffusion cell into the solution. The measurement solution is then propelled in the reverse direction to feed into the measuring cell. In the measuring cell, the measurement solution is electrochemically measured to determine a value which is related to the partial pressure of oxygen (pO.sub.2) in the sample.

Abstract: A method for producing a liquid phase substance having a pre-established concentration of CO.sub.2 suitable for calibrating analytical instruments such as hemogasanalyzers consists in:preparing an aqueous solution of precisely known strength of a water-soluble salt of carbonic acid,then transferring said solution to a flow reactor containing a cation exchange resin in hydrogenionic form,passing the aforesaid solution of carbonic acid salt through the aforesaid cation resin,thereby achieving the reaction of producing a pre-established quantity of CO.sub.2, andtransferring the eluate thus obtained directly to the analytical instrument for calibration.