Abstract: The present invention relates to a sensor for determining the concentration of an acidic or basic compound dissolved in water, wherein the determination is based on an ingress of gas or vapor of said compound, causing a change in pH value, within an inner buffer separated from a sample side by a membrane that is permeable to gases and impermeable to ions, characterized in that a layer is provided between the membrane and the sample side, wherein the layer substantially covers the membrane, wherein the layer is water-soluble and has pH buffering properties. The present invention further relates to the use of a water-soluble layer having pH buffering properties for protecting a sensor for determining the concentration of an acidic or basic compound from ingress of an acidic or basic gas during non-use of the sensor.

Abstract: An sensor (2) based on an optical-sensing technique measures gaseous or dissolved analytes in a measurement medium (4). The sensor has a sensor housing (6) and an optochemical sensor element (20, 220) arranged within the sensor housing. The optochemical sensor element (220) has a substrate (222), a sensing layer (224) and a barrier layer (230). The barrier layer is arranged to protect the optochemical sensor element from interfering substances (234) present in the measurement medium.

Abstract: An sensor (2) based on an optical-sensing technique measures gaseous or dissolved analytes in a measurement medium (4). The sensor has a sensor housing (6) and an optochemical sensor element (20, 220) arranged within the sensor housing. The optochemical sensor element (220) has a substrate (222), a sensing layer (224) and a barrier layer (230). The barrier layer is arranged to protect the optochemical sensor element from interfering substances (234) present in the measurement medium.