Passive sampling instrumentation

However, standard deviations and detection limits are better for automatic than for manual analysis especially if the latter involves a passive sampling-solvent desorption method. This is a consequence of the many sources of errors possible in a manual method which are not present in automatic instruments. 

Analysis of 02 as well as C02 in exhaust gas is becoming generally accepted and is likely to be applied as a standard measuring technique in bioprocessing. It is possible to multiplex the exhaust gas lines from several reactors in order to reduce costs. However, it should be taken into account that the time delay of measurements with classical instruments is in the order of several minutes, depending on the efforts for gas transport (active, passive) and sample pretreatment (drying, filtering of the gas aliquot). 

ACAMS alarms must be verified to ensure that they are not a false positive due to an interferent species or instrument malfunction. This verification is done using a depot area air monitoring system (DAAMS) deployed near an ACAMS. DAAMS is a passive system that draws an air stream through a sorbent tube. The tubes are collected and replaced periodically if there are no ACAMS alarms or shortly after an alarm occurs. They are transported to a laboratory and thermally desorbed onto a sample tube and analyzed on a laboratory scale GC/FPD system. Without confirmation by the more sensitive... 

Although adsorption experiments with H-beta gave results in accordance with the preference for the linear product from 3-heptanone phenylhydrazone, with a bulky/linear adsorption ratio of 28/72 being found [23], and similar results were obtained for the indole isomers from 1-phenyl-2-butanone [22], total adsorption was small. Furthermore, when a sample of beta, the external surface of which had been passivated by silylation [24], was employed, no activity was found. This strongly suggests that it is the external surface, rather than the internal pore walls, which is responsible for the activity observed, thus variations in isomer distribution cannot be ascribed to pore-induced shape selectivity. Comparison of the calculated relative stabilities of the isomeric enehydrazines and indoles with the selectivity data of Table 1 indicate that the reactions are kinetically controlled, so that factors such as solvent effects are probably instrumental in establishing the observed product ratios. 

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