General description of Purge and trap

principle:

1. Purge: phase transfer of analyte(s) with relatively large air/water partition constants from an aqueous phase W into gas bubbles created by purging the sample
   
   non-volatile interferents remain in water sample
   
      
2. Trap: Phase transfer of analyte(s) from purge gas to solid sorbent in a filter unit
   
   pre-concentration of analyte in the sorbent
   
   
3. Thermal desorption of analyte from the sorbent in an oven connected to the GC column