Liquid media detectors

Chemically active plastics such as the polyelectrolytes have been used to make artificial muscle materials. This is an unusual type of mechanical power device that creates motion by the lengthening and shortening of fibers made from a chemically active plastic by changing the composition of the surrounding liquid medium, either directly or by the use of electrolytic chemical action. Obviously this form of mechanical power generation is no competitor to thermal energy sources, but it is potentially valuable in detector equipment that would be sensitive to the changing... 

A well-defined volume of the gaseous sample is directed towards the flow manifold, where it interacts with a liquid medium, and the chem-iluminometric determination of nitrous acid in an indoor environment [18] is a good example. A calibrated vacuum pump aspirated the volume of air through a diffusion scrubber and the membrane-separated analyte was collected into a buffered stream that directed it towards an 8-port injection valve after passing a de-bubbler, the analyte zone was directed towards the detector. With this approach, a 120 pp tv detection limit was attained. The characteristics, potential and limitations of analytical procedures involving diffusion scrubbers and other devices for gas sampling aimed at in-line flow-based determinations have been discussed elsewhere [19]. 

The highest throughput can be achieved by the combination of flow cytometry and cell sorting. This is a rapid method for the analysis of single cells as they flow in a liquid medium through the focus of a laser beam surrounded by an array of detectors. By simultaneous use of different fluorescent stains, flow cytometry can yield multiparametric data sets which are, however, often difficult to interpret [88]. These are then used to discriminate between different types of cells, a procedure that is suitable for rapid enrichment of certain types of cells from large populations. An important and potentially very useful contribution to flu-... 

Numerous commercial oxygen analysers are available, based on the principle of the Hersch cell, but all being protected from the analyte medium, either gaseous or liquid, by means of a membrane (usually Teflon). This membrane detector is known as the Clark cell (see later under membranes as measurement aids, p. 352) for gas analysis we may mention the Beckman Models 715 (also for liquids), 741, 743 (for flue gas), 755 and 778119. 

Without a method or mechanism to detect a catastrophic, or even a small release from an inner wall, the use of a secondary outer wall is superfluous. A failure in the inner wall will certainly lead to a failure of the outer wall if the failure goes unnoticed and no action is taken. The secondary wall may delay the release, but release would be inevitable without annular space detection. Typical detection mechanisms include gas analyzers or pressure detectors for vapors, conductivity switches for liquids, or weep holes routed to drain systems that are periodically monitored (Prugh, 1992). A purge gas is sometimes used as a detection medium, to reveal a change in contaminants in the purge gas exhaust (CCPS, 1988b). 

Molecules set in motion by the mobile phase (eluent) move through the stationary phase, suitably immobilized on a medium. The higher the affinity for the stationary phase and the lower the affinity for the mobile phase, the slower the analyte. As in a race, the fastest chemical species cover a prearranged distance in the shortest time, arrive at the finish line, and produce a detector signal proportional to the amount of analyte. The aggregation state of the mobile phase enables us to differentiate liquid, gas, and supercritical chromatographic techniques. 

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