Amperometric solution-phase sensors

Herschkovitz et al. ([69] Section 3.3.3.2) reported formaldehyde, a major air pollutant, detection in solution phase based on the coupling of a biosensor measuring device and a flow injection system. Amperometric formaldehyde sensor was constructed using screen-printed carbon ink electrodes modified with osmium-based hydrogel and then placing formaldehyde dehydrogenase immobilized nylon membrane directly onto the electrode. The sensor is selective, inexpensive, stable over several days, easy to construct and... 

The Clark electrodes described above are not suitable for oxygen determination in dry gaseous samples such as air because the thin layer of electrolyte solution contained behind the membrane is prone to rapid drying. A different arrangement is therefore used for such applications. Amperometric gas sensors for oxygen (and sensors for other electroactive species in the vapor phase) usually consist of a porous PTFE membrane that bears a precious metal electrode deposited, also in porous form, directly on the backside. This keeps the diffusion length short while... 

Numerous catalytic layers made by different immobiUzing techniques have been used to enhance the selectivity of amperometric sensors. One example chosen from a large variety was a platinum microelectrode coated with polyvinylpyridine carrying a layer of anodicaUy deposited paUadium/iridium oxides (Shi et aL 2001). Polyvinylpyridine is an electricaUy conducting polymer. The sensor has been used to determine sulphur dioxide in gaseous phase as weU as sulphite in solution. 

This applies to another possible way of non-electrolytic accumuladcm, based on spontaneous transfer and distribution of a species between two liquid phases, typically from an aqueous solution into a non-polar medium, when the role of exchanged species can be attributed to neutral molecules or ion associates with compensated charge. This is accompUshed with the liquid binder in carlxMi paste mixtures or by liquid membranes coating the tips of potentiometric or amperometric sensors. In both cases, extraction (Eq. 5.12a) and the reverse process, re-extraction, take place in the electrode bulk ( ELB ) before the release from the interior to the aqueous phase ( AQ ) and the final disintegration during detection (Eq. 5.12b) ... 

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