Sensor coulometric

The ISFET-based integrated coulometric sensor-actuator system was introduced in 1985 [154] in order to facilitate in situ calibration of ISFETs. The essential components of a prototype sensor based on this operational principle are shown in Fig. 4.20.B. The system was built by integrating a large noble-metal actuator electrode and a counter-electrode in a piece of silicon. A window in the actuator electrode was etched to receive the gate of the ISFET, which functioned as a pH indicator. The flow-through cell was constructed by sealing a silicon cover with an etched cavity of the chip. The system operation resembles that of a conventional coulometric titration system very closely. The sample was first injected into the cavity and the... 

Figure 4.20 — (A) Detailed side view of a double-sensor flow-cell 1,2 Perspex 3 contact wire 4, CHEMFET. (B) Scheme of a microlitre coulometric sensor. (Rqtroduced from [152] and [154] with permission of Elsevier Science Publishers).

ASTM D3985, 2002. Standard test method for oxygen gas transmission rate through plastic film and sheeting using a coulometric sensor. 

ASTM Standard D-3985, "Standard Test Method for Oxygen Gas Transmission Rate through Plastic Film and Sheeting Using a Coulometric Sensor" in Part 35 of Annual Book of ASTM Standards, American Society for Testing and Materials, Philadelphia, Revised Annually. 

The slope of the measured titration curve is inversely proportional to the buffer capacity of the protein, which contains specific information on the type of protein. After modification of the coulometric sensor-actuator device with a porous gold actuator electrode, the device is shown to be suitable for the determination of protein buffer capacity in solution [17]. A schematic representation of the device is shown in Fig. 12. The buffer capacity can be measured by sending a small alternating current through the porous actuator electrode, resulting in the alternating generation of protons and hydroxyl ions. This will result in a small pH perturbation in the free space of the porous electrode, which is detected by... 

FIG. 10 Typical titration curves measured with a coulometric sensor-actuator device at 5 nA generating current before and after the mentioned number of minutes of incubation in 3- I0-5 M lysozyme. 

FIG. 12 Basic elements of the coulometric sensor-actuator system based on an ISFET with gate-covering porous actuator electrode. The thickness of the porous actuator is about 100 /pore size is about I /mi. 

Amperometric sensors are based on the electrochemical reduction of oxygen, and are governed by the diffusion of the electroactive species through a barrier - that is, holes or porous layers 81,82], The coulometric sensors are based on a similar concept, and were developed for closed-chamber systems. Although very few amperometric and coulometric sensors have been studied to date, some relevant examples are summarized in Chapter 13. 

Permeability of Thermoplastic Containers to Packaged Reagents or Proprietary Products Oxygen Gas Transmission Rate Through Plastic Film and Sheet using a Coulometric Sensor Water Permeability of Geotextiles by Permittivity Permeability of Leather to Water Vapor... 

Auras and co-workers [51] studied the variations in the oxygen diffusion, solubility, and permeability coefficients of polylactide films at different temperatures (5, 23 or 40 °C) and water activities (0-0.9). A modified Ox-Tran 100-Twin with a coulometric sensor (Mocon, Inc., Minneapolis, MN, USA) was used for measuring the permeability of oxygen through the polymer films as a function of the water activity (A ) which is... 

Bergveld (7 ) was, of course, the first to report an ISFET as a chemically sensitive semiconductor device (CSSD). A broader grouping is that of chemically sensitive electronic devices CSEDs), sub-classified by Bergveld and van der Schoot (75) into ISFETs as "active electronic components as one member of a four-class system. Other categories are passive electronic components (resistor, capacitor, etc.), electronic and opto-electronic systems (oscillating crystal sensors, etc.), and systems with a chemical feedback (dynamic oxygen sensor, and coulometric sensors). 

The working principle for amperometric sensors and coulometric sensors is the same. A fixed potential (the value on the plateau region from the voltammogram) is applied and the current passing through the cell is recorded as a function of time. The current measured can be... 

Broader utilization of coulometric sensors for in situ analytics... 

Coulometric sensors are constructed, on the other hand, so that practically all the species to be determined is depleted by electrolysis during passage through the sensor and C2 < 0,01 Ci At the constant v the current is given by Faraday law... 

PERFORMANCE OF THE COULOMETRIC SENSOR-ACTUATOR DEVICE IMPROVED BY jTAS... 

The ISFET-based coulometric sensor-actuator device turns out to be well suited for lTAS applications, because there is no need for a reference electrode. It is shown that XTAS essentially can improve the performance of the sensor-actuator device, with respect to its ease of operation (no interfering mass transport, an excess concentration of supporting electrolyte is available and signal processing is simpler) and its measuring range (controlled dilution). 

When the coulometric sensor-actuator chip is glued on a small printed-circuit board carrier, a dipstick-like titrator is obtained, capable of performing fast titrations (seconds) in a small sample volume (microliters). Operation in a larger volume has the advantage that the bulk of the solution is not affected by the titration. The titration is fully computer controllable and does not require extra chemicals. 

Unfortunately, the coulometric sensor-actuator device shows some disadvantages, which can be made clear by presenting the result of a series of measurements in figure 4. 

In this section, the basic building blocks of xTAS are considered to be available or at least, the fabrication of these blocks is considered to be feasible. With basic building blocks, subsystems of liTAS are meant that are capable of performing a well-defined function, like inlet, selection valve, micro-pump, injector, mixing chamber, reaction chamber, outlet, etc. It will be shown that with the availability of these subsystems, the performance of the coulometric sensor-actuator device can be essentially improved. 

Fig. 6 The proposed pTAS for improved coulometric sensor-actuator performance.

It has been the purpose of this paper to show that the performance of an already existing sensor can essentially be improved by the subsystems that are present in a pTAS. Concerning the coulometric sensor-actuator device, which is very well suited for integration in a pTAS by its lack of need for a reference electrode, the following is gained in combination with a pTAS ... 

W. Olthuis, J. Luo, B.H. van der School, P. Bergveld, M. Bos and W.E. van der Linden, Modelling of non-steady-state concentration profiles at an ISFET-based coulometric sensor-actuator system, Anal. Chim. Acta, 237 (1990) 71-81. 

The term coulometric sensor is somewhat misleading. Coulometry, in its original sense, means to measure the amount of charge (the current-time product) for an electrochemical reaction and to calculate the corresponding amount of substance. Commonly, for reactions considered in this way, the total... 

Coulometric sensors are very similar to the amperometric devices. The gas species is dosed by the faradaic effect, but, in this case, the diffusion flux between the chamber and the analyzed atmosphere is negligible dining the measurement. The current pumps the internal partial pressure (PjJ from the external value (Pout)> which corresponds to equilibrium condition, to zero or from zero to P t. The electroactive gas is supposed to be an ideal and so its partial pressure is equal to... 

There are two kinds of coulometric sensors. Both work with two steps. In the first kind, the measurement is made during an electrochemical purge of the chamber (from P to zero) and in the second kind, the measurement is made during an electrochemical enrichment (from zero to Pout). 

FIGURE 10.14. Closed-chamber device of a coulometric sensor (oxygen sensor). 

If amperometric sensors work with constant U, the response time can be short and they can be used in real-time measurements. On the other hand, for a multispecies analysis system, it is necessary to draw the entire 1(U) curve (or to use a data acquisition system) to locate the different diffusion plateaus. Such sensors, like coulometric sensors, are more adapted for... 

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