Particulate vapor test atmospheres, generator

Figure 8. Glass generator for particulate/vapor test atmospheres...

When insufficient data are available, it may be necessary to generate test atmospheres to determine the physical state of a compound and the collection efficiency of a filter and vapor collector. The estimation of the vapor/particulate ratio may also depend on concentration and sample loading. For example, in a short sampling time, vapor may be efficiently collected on a filter, but longer term sampling may reveal saturation of the filter with vapor and eventual passage of the vapor into a backup bubbler or sorbent tube. 

If the ratio EVC/std is in the range 0.05 to 100-300, then a mixture of particulate and vapor may be present (7). A ratio above this range indicates the presence of vapor alone and below the range, particulate. The reliability of this determination depends on the accuracy of vapor pressure data. In method development and validation studies, it is often necessary to perform special tests with generated test atmospheres at different temperatures and concentrations to demonstrate the physical form of the substance. 

Laskin-Type Nozzle Generator. A third type of atomizer, the Laskin-type nozzle generator, is used to create test atmospheres of particulate or aerosol and vapor mixtures. A pure liquid or melt is used, and no solvent is necessary. Again, this is important for evaluating filter and solid sorbent combination sampling trains. 

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