Differential sensor

The previously used flow sensor option in research fuel cells were the integrated circuit (IC)-type differential sensors, which were limited by their low tolerance for water contamination. This was a serious limitation in reforming-type fuel cell applications, because the presence of water is essential for the operation of the system, and no protection against water contamination was provided in the smaller and cheaper IC sensors. 

Pressure differential sensors for purging (7a) and operational state of the p-apparatus (7b), acting on the regulated pressure relief valve (3) with (normally) a higher internal overpressure during purging and a somewhat lower internal overpressure in the operational mode... 

Finally combinatorial methods for the fabrication of chemical sensors have been proven to enhance significantly the performance of differential sensors. In this chapter, we show the use of a combinatorial parallel fabrication of fluorescent SAMs. 

Abstract We review recent progress in wide bandgap thin-film and nanorod sensors made from GaN or ZnO and related materials for applications in the detection of gases such as oxygen, carbon dioxide and hydrogen. Practical aspects are covered, such as the use of differential sensor pairs to eliminate the effects of temperature variations and of the effect of humidity on the detection sensitivity. 

Figure 10 illustrates the results obtained for such a differential gas sensor cell arrangement. Varying concentrations of ammonia were generated by adding ammonium chloride standards to a 0.01 M NaOH sample solution. The slope of the differential sensor is 93.6... 

Fig. 7 Illustration of a differential sensor design for measuring carbon dioxide levels in biological fluids using two identical planar polymer membrane pH sensors with different internal solutions.

Severin etal recently pnblished another successful array for differentiating peptides by employing three commercially available metal complexes (27-29). One complex contained rhodium, one ruthenium, and one palladium. In the presence of six selected fluorophores, these constituents formed a collection of differential sensors. The receptors were able to differentiate 10 dipeptides at a 50 pM concentration (the closed symbols in Figure 9) and 2 dipeptides at 20 pM concentration (the open symbols in Figure 9). The authors found that peptides containing histidine and methionine residues were best discriminated, most likely because these residues displaced a larger fraction of... 

This rationale led Severin et alP to construct an array consisting of CuCh, NiCh, and three UV-active chro-mophores, resulting in six metal-indicator combinations to comprise a dynamic combinatorial library. A dynamic combinatorial library is an array of differential sensors that are simultaneously present in one solution, under thermodynamic control, such that this one solution can provide multiple signals from the composite interactions of an analyte with all the sensors in solution. They found that this simple dynamic combinatorial library of receptors was able to successfully discriminate two angiotensin peptides (angiotensin I and angiotensin II) and mixtures of these two peptides. 

The power of array sensing is most apparent when discriminating multianalyte solutions. In such solutions, multiple compounds (possibly hundreds or even thousands) make up each mixture. Array sensing is ideal for such a situation, with its inherent ability to detect multiple analytes simultaneously using various differential sensors, especially in circumstances where the multianalyte solutions have only subtle differences in chemical compositions. The resultant fingerprint response achieved for each solution allows discrimination through pattern recognition. 

The pressure P is often not very different from the saturating vapor pressure of the pure substance P°. To improve the accuracy, therefore, it is preferable to work with a differential measurement. We use a pressure-differential sensor, which measures the difference in pressure that exists between two tanks placed in a thermostatic chamber at the chosen temperature. In one tank, equilibrium is established between the pure component and the vapor phase, and in the other, that equilibrium is established between the solution and the vapor phase. The saturating vapor... 

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