Gas-Liquid Separations
Fouling of membrane separators is avoided in gas expansion separation. Unfortunately, gas expanders cannot be miniaturized , and therefore they have been used mainly for AA and ICP assays for hydride generation, and as interface between FI and SI instruments and systems emitting volatiles and gases.
Gas expansion separators are robust and easy to construct and maintain. The entire separator, or at least its vertical tubular body, is made of glass, and often partially filled with large glass beads, since a hydrophilic glass surface assists in gas-liquid separation. A carrier/hydrogen/hydride stream generated in FI system is joined with a purging gas (air, nitrogen or argon) that sweeps the liquid in the separator and carries the released volatiles into the detector. The level of liquid in the separator is maintained by an external pump. Gas expansion separators are operated at high flow rates; the combined flow of sample, reagent and carrier is up to 15 mL/min, and a purging gas flow rate of 30 mL/min is not unusual. In comparison, membrane separators offer higher sensitivity at lower flow rates, since their internal gas volume is much smaller. (Fang 1988, Hansen and Miró 2008)
1.3.17.
