Vapor/Solid chemisorption model for passive sampling of aldehydes

The vapor-phase chemisorption isotherms of valeraldehyde (n-valeraldehyde; 1-pentanal) and acrolein (2-propenal) above the critical face velocity (7.5 cm/s) were investigated at 25 degrees C and 36 percent relative humidity (RH) for a passive air sampling pellet of 10 percent O-(2,3,4,5,6-pentafluorobenzyl)-hydroxylamine hydrochloride (PFBHA) on Tenax TA solid sorbent (80/100 mesh). A dynamic air dilution system with syringe pumps generated the vapor concentrations and humidity for the exposure chamber. The O-oxime derivatives were desorbed with hexane for gas chromatographic analysis on a nonpolar capillary column and electron capture detection. The pellet capacity was about 30 micromoles. Adsorption of valeraldehyde was best fitted by a Langmuir or Brunauer-Emmett-Teller (BET) I model. That for acrolein was described best by a Dubinin-Radushkevich model. A microporosity model explained why all the classical isotherms described the chemisorption behavior. An activated extrinsic precursor was suggested to facilitate the addition reaction by production of a protonated intermediate formed by the transfer of a proton to the aldehyde from an activated reaction site consisting of at least 2 PFBHA molecules.