Variables influencing analytical pervaporation

Most often, the aim of manipulating the variables that influence a method is improving its efficiency, both by lowering the limit of determination and by obtaining a steeper slope for the calibration curve. When the concentration of the target analyte in the sample 

Solid sample treatments involving the removal oj volatile species 

An increase in temperature in the donor chamber increases the vapour pressure of the analyte and boosts mass transfer across the membrane. The usual way of heating this chamber is by immersing it into a water bath. When pervaporation is assisted by micro-waves focused on the donor chamber, higher temperatures can be reached with closer control [28]. Different working temperatures result in calibration curves that encompass different analyte concentration ranges (see Fig. 4.20), which can be of interest when the concentration of the target species in the sample ranges over wide bounds. 

Reducing the air gap space also increases the likelihood of sample-membrane contact, so a compromise between sensitivity and selectivity must be adopted. 

With liquid samples, Xhe flow-rate strongly influences the pervaporation process. The lower the flow-rate is, the longer will be the residence time in the donor chamber of a given volume of sample and the closer to equilibrium will be the analyte mass transfer. The flow can be stopped when the sample is in the donor chamber to allow steady-state mass transfer. This situation is not desirable because it lengthens the separation unduly. Instead, a fresh sample can be passed through the donor chamber as often as required provided the volume of sample available is not limited. 

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