Fouling sensor

On-site measurement thus seems to be the optimal solution for wastewater quality monitoring. However, as seen previously, wastewater composition is very complex and varyies with time and space. The implementation of on-site measurement must take into account some constraints related to the risk of sampling line clogging or sensor fouling (in the case of on-line measurement). In order to prevent this risk, or at least to space maintenance procedures, on-site measurement must be carried out carefully, depending on the type of system used. 

A further level of sophistication is illustrated by a submersible UV/vis spectrometer, currently being developed for batch process analysis but potentially also applicable to continuous processes. This instrument also overcomes the sensor-fouling problem by using an auto cleaning system based on pressurised air [76]. 

A similar experiment was conducted after the sensor was implanted in the rat for 5 h. This experiment was done to test whether implanting the sensor fouls the surface and alters the partitioning and departitioning of glucose. The sensor was removed from the rat and immediately placed in a flow cell containing bovine plasma to simulate the in vivo environment. The 1/e time constant was then determined... 

Sources of Error. pH electrodes are subject to fewer iaterfereaces and other types of error than most potentiometric ionic-activity sensors, ie, ion-selective electrodes (see Electro analytical techniques). However, pH electrodes must be used with an awareness of their particular response characteristics, as weU as the potential sources of error that may affect other components of the measurement system, especially the reference electrode. Several common causes of measurement problems are electrode iaterferences and/or fouling of the pH sensor, sample matrix effects, reference electrode iastabiHty, and improper caHbration of the measurement system (12). 

Fouling of the pH sensor may occur in solutions containing surface-active constituents that coat the electrode surface and may result in sluggish response and drift of the pH reading. Prolonged measurements in blood, sludges, and various industrial process materials and wastes can cause such drift. Therefore, it is necessary to clean the membrane mechanically or chemically at intervals that are consistent with the magnitude of the effect and the precision of the results requited. 

A major disadvantage is that the direct sensor detection cannot distinguish between the sensor response to the specific analyte binding from the response to a possible nonspecific adsorption of other compounds. The nonspecific fouling from blood or blood serum seems to be one of the main barriers for practical application of immunosensors in medical diagnostics. 

Sensor hysteresis and fouling Not selective to hydrogen Limited operation range... 

On-line Representativity Fouling Availability Good positioning of sensor Anti-fouling devices Adapted service Double sensing preferable... 

Acoustic chemometrics has its greatest benefits in cases where haditional sensors and measurement techniques, such as flow, temperature and pressure transmitters cannot be used. In many processes it is preferable to use noninvasive sensors because invasive sensors may cause disturbances, for example fouling and clogging inside the process equipment such as pipelines, reactors cyclones, etc. In this chapter we concentrate mainly on new industrial applications for acoustic chemomehics, and only discuss the necessary elements of the more technical aspects of the enabling technology below - details can be found in the extensive background literature [3-5],... 

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