Diffusional monitoring

For the diffusional monitor the steady state mass transport... 

In this paper, data is cited which demonstrates that diffusional monitoring can be used in circumstances in which pumps and charcoal tubes were previously used. The data cited emphasizes the comparability of diffusional monitoring to charcoal tube and pump. However, it must be noted that the methods are different, and will not in each circumstance yield comparable results. The most conclusive tests will be those which employ a third method (e.g., gas chromatography, infrared analysis) capable of accurately determining the contaminant, or contaminants concentration. 

The diffusional monitoring system is a much simpler, easier method to present a sample of organic vapor to a charcoal collector. It eliminates mechanical problems of pumps and in the case of the 3M system, provides for elution inside the monitor body, rather than forcing transfer of the sorbent. It has a wide dynamic range, a quick response to... 

The theory and practical use of a diffusional monitor is described. The diffusional monitor can be used to accurately measure personal exposures, as well as to determine area concentrations of organic vapors. 

Changes in fluidity of a medium can thus be monitored via the variations of Jo/J — 1 for quenching, and Ie/Im for excimer formation, because these two quantities are proportional to the diffusional rate constant kj, i.e. proportional to the diffusion coefficient D. Once again, we should not calculate the viscosity value from D by means of the Stokes-Einstein relation (see Section 8.1). 

Persson, L.B., G.M. Morrison, J.U. Friemann, J. Kingston, G. Mills, and R. Greenwood. 2001. Diffusional behaviour of metals in a passive sampling system for monitoring aquatic pollution. J. Environ. Monit. 3 639-645. 

Using AW devices to monitor dynamic processes such as diffusion and corrosion can dramatically reduce the time required to quantify these processes. For example, as discussed in Section 4.2.2, diffusion equilibration times typically increase with the square of the diffusional length. For a thin film, this length scale, the film thickness (h), is very small. This enables the quantification of diffusion coefficients as low as 10 cm /sec in less than one day, whereas months would be required using many conventional techniques that use thick films or bulk samples. For corrosion monitoring, the dramatic decrease in mass detection limits obtainable using coated AW devices, as compared with conventional balances and sample coupons, allows detectable mass changes to be achieved in minutes or hours rather than days or months (Section 4.4.3). 

The wide variability of absorption and diffusional properties of chemical species in organic polymer films makes them useful as selective or complete permeation barriers (e.g., gas separation membranes and passivating layers [1,5,82]) and selective chemical sensor coatings [83]. For these applications, a method for rapidly and directly evaluating the solubility and diffusional properties in thin films is useful. Diffusional properties can be evaluated by monitoring the transient up-... 

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