Analyte stability sorbed

The sorbent materials that performed best in the capacity and desorption efficiency tests were investigated further with respect to the stability of the sorbed analyte. Preliminary tests of analyte stability were conducted by a procedure similar to that in the desorption efficiency tests the procedure differed in that samples were stored 7 d prior to analysis rather than Id. To be acceptable, a sorbent material had to exhibit no statistically significant loss of analyte at the 0.05 significance level by a two-tailed t test. 

Initially, tests were performed to determine the LAQL for each analyte. The long-term stability of each sorbed analyte at its LAQL was also determined. Finally, the accuracy and precision of the analytical method alone and also the overall accuracy and precision of the combined sampling and analytical methods were determined. All tests were performed with the previously developed analytical procedures and sampling devices. 

Determination of Long-Term Stability of Sorbed Analyte. 

Tests were performed to determine the stability of sorbed analytes in tubes that had been exposed to generator effluent and that were then stored for at least 7 d. For each method, the analyte concentration in the generator effluent was maintained at about 0.3 X LAQL per liter 3 L of the generator atmosphere was sampled at a rate of 0.2 L/min to yield a tube loading of about the LAQL. Following exposure, the sorbent tubes were sealed with Teflon tape and plastic caps for storage. 

Appropriate SPE sorbent selection is critical to obtaining efficient SPE recovery of semivolatile organics from liquids. Henry [58] notes that an SPE sorbent must be able to sorb rapidly and reproducibly, defined quantities of sample components of interest. Fritz [73] states that successful SPE has two major requirements (1) a high, reproducible percentage of the analytical solutes must be taken up by the solid extractant and (2) the solutes must then be easily and completely eluted from the solid particles. The sorption process must be reversible. In addition to reversible sorption, SPE sorbents should be porous with large surface areas, be free of leachable impurities, exhibit stability toward the sample matrix and the elution solvents, and have good surface contact with the sample solution [68,73],... 

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