Abstract: An electrode device for the determination of the partial pressure of CO.sub.2, Pco.sub.2, in particular an electrode device for transcutaneous determination of Pco.sub.2.The interior electrolyte of the electrode device is adapted to the exterior electrolyte in such a manner that the potential difference measured over the exterior reference electrode and the interior reference electrode is substantially temperature-independent with a temperature dependence for the CO.sub.2 partial pressure determination in the range of -1%/.degree.C.-+1%.degree.C.The interior electrolyte preferably contains a pH-buffer system based on phenyl phosphonic acid.

Abstract: Salt bridge liquid for use in potentiometric measurement of blood or a blood liquid.The salt bridge liquid contains Na.sup.+ -ions and HCOO.sup.- -ions in substantially equimolar amounts, preferably in a concentration larger than or equal to 1 M, in particular about 4 M.When this salt bridge liquid is used, the potentiometric measurement will give corresponding results when measuring a blood sample and the corresponding plasma sample because the suspension effect which is caused by the erythrocytes and which is seen when using other salt bridge liquids is substantially eliminated. Furthermore, different blood samples with the same ion concentration but with varying erythrocyte content will give corresponding measuring results.