Flow-through chemical sensors reaction-rate

On the other hand, its should be emphasized that such basic analytical properties as precision, sensitivity and selectivity are influenced by the kinetic connotations of the sensor. Measurement repeatability and reproducibility depend largely on constancy of the hydrodynamic properties of the continuous system used and on whether or not the chemical and separation processes involved reach complete equilibrium (otherwise, measurements made under unstable conditions may result in substantial errors). Reaction rate measurements boost selectivity as they provide differential (incremental) rather than absolute values, so any interferences from the sample matrix are considerably reduced. Because flow-through sensors enable simultaneous concentration and detection, they can be used to develop kinetic methodologies based on the slope of the initial portion of the transient signal, thereby indirectly increasing the sensitivity without the need for the large sample volumes typically used by classical preconcentration methods. 

Electric heaters are usually applied for calibration of calorimeters, especially for heat-flow instruments equipped with thermopiles or Peltier sensors. But often a chemical calibration is more appropriate and matching the experimental conditions more closely. For this end Wadso and coworkers recommended the hydrolysis of triacetin in imidazole/acetic acid buffer with stable, long-lasting heat production rates between 7 and 90 pW/mL at 37 °C [142,143]. Some other possible reactions were cited and discussed in connection with the most important types of calonmetric vessels, batch forms as well as flow-through containers. 

Many chemical reactions are nonisothermal. In order to carry out a particular reaction, we must maintain the temperature of the reaction volume within some limits to avoid species decomposition. In particular, exothermic reactions are problematic. We need to be able to eliminate the generated energy so that we can maintain the reaction under control. Let s consider a system of a jacketed stirred tank reactor where we need to control the temperature by means of the flow rate through the jacket and that there is a perturbation in the flow that feeds the reactor. In our system, we have a controller, a valve, the actuator, the system, our reactor, the perturbation, and a sensor see Figure 4.33. 

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