Sensors liquid filled

The products of hybridization are detected through the use of fluorescent labeling. These molecular complexes can either be homogeneously distributed in the liquid core or be bound to the interior surface of the capillary through covalent bonding. In both cases, labeled molecules can be excited either by direct illumination with the leaky modes of the liquid filled core, or by the evanescent waves arising from the guided modes of the capillary wall. Direct excitation is less wasteful of incident photon flux and is the method of choice in conventional fluorometers. Evanescent wave excitation becomes a necessity when direct excitation is either not feasible or results in undesirable sensor performance. Both methods of illumination are possible for the CWBP. 

Martin A.J. Green M. Sol-gel nano-porous silica-titania thin films with liquid fill for optical interferometric sensors. Proc. Soc. Photo-Instrumentation Eng. 1990 1328 352-362... 

If, however, solid electrolytes remain stable when in direct contact with the reacting solid to be probed, direct in-situ determinations of /r,( ,0 are possible by spatially resolved emf measurements with miniaturized galvanic cells. Obviously, the response time of the sensor must be shorter than the characteristic time of the process to be investigated. Since the probing is confined to the contact area between sensor and sample surface, we cannot determine the component activities in the interior of a sample. This is in contrast to liquid systems where capillaries filled with a liquid electrolyte can be inserted. In order to equilibrate, the contacting sensor always perturbs the system to be measured. The perturbation capacity of a sensor and its individual response time are related to each other. However, the main limitation for the application of high-temperature solid emf sensors is their lack of chemical stability. 

The magnitude of the dissociation constant A plays an important role in the response characteristics of the sensor. For a weakly dissociated gas (e.g., CO2, K = 4.4 x 10-7), the sensor can reach its equilibrium value in less than 100 s and no accumulation of CO2 takes place in the interior layer. On the other hand, SO2, which is a much stronger acid (K = 1.3 x 10-2), accumulates inside the sensor and its rep-sonse time is in minutes. The detection limit and sensitivity of the conductometric gas sensors also depend on the value of the dissociation constant, on the solubility of the gas in the internal filling solution, and, to some extent, on the equivalent ionic conductances of the ions involved. Although an aqueous filling solution has been used in all conductometric gas sensors described to date, it is possible, in principle, to use any liquid for that purpose. The choice of the dielectric constant and solubility would then provide additional experimental parameters that could be optimized in order to obtain higher selectivity and/or a lower detection limit. 

Solid-state ion sensors with conducting polymers as ion-to-electron transducers (and sensing membranes) offer some advantages over conventional liquid-contact ISEs. Solid-state ISEs without internal filling solution are more durable, require less maintenance, are easier to miniaturize, and allow great flexibility in electrode design and fabrication. 

With those single-mode reactors that do not require a minimum filling volume (CEM Discover platform temperature measurement is performed from the bottom and not from the side by an external IR sensor) even volumes as low as 50 xL can be processed [57]. With the commercially available singlemode cavities of today, the largest volumes that can be processed under sealed vessel conditions are ca 50 mL, with different vessel types being available to upscale in a linear fashion from 0.05 to 50 mL. Under open vessel conditions higher volumes (> 1000 mL) have been processed under microwave irradiation conditions, without presenting any technical difficulties as, e.g., described for the synthesis of various ionic liquids on a 2 mol scale [35]. 

Liquid level can be detected (inferred) by measuring a d/p. The high-pressure side of the d/p cell is connected to the bottom of the vessel, and the low-pressure side (reference) to the vapor space is connected above the liquid (pressurized tanks) or is vented to the atmosphere (atmospheric tanks). In atmospheric HTG, the low-pressure side reference leg must produce a constant head either by a column of fluid of fixed height (reference leg) or by a gas-filled reference leg. The sensor can be direct-acting (0 to 100%) d/p or reverse-acting (100 to 0%), and the densities (therefore temperatures also) of both process and reference liquids must be constant. 

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