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Abstract

An improved optical probe for the invasive measurement of partial carbon dioxide pressures is disclosed that minimizes pCO.sub.2 reading drift. An optical probe for the invasive measurement of the partial carbon dioxide pressure comprises an optical fiber and a pCO.sub.2 sensor. The pCO.sub.2 sensor comprises a diffusion zone with a dye-containing gel that is optically sensitive to H.sup.+ ions and a semi-permeable membrane that is permeable to CO.sub.2 molecules, but is substantially nonpermeable to hydrogen ions Components of the pCO.sub.2 sensor, such as the part of the optical fiber extending into the sensor or a reflector, are covered with a substance--preferably with a coating--that is substantially nonpermeable to hydrogen ions. This prevents the hydrogen ions from diffusing into the sensor components, which otherwise would cause an imbalance of hydrogen ions and, therefore, a drift in the pCO.sub.2 reading.

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First Claim