Selective gas-phase capture of explosives on metal β-diketonate polymers

A variety of metal β-diketonate polymers were assessed for gas-phase selective retention of nitro aromatic, nitrate ester, and peroxide explosives. The La(III) complex of p-di(4,4,5,5,6,6,6-heptafluoro-1,3-hexanedionyl)benzene [La(dihed)] showed 13–42 times the retention for the nitro aromatic compounds compared to a control column (identical column but lacking the 5% loading of the metal β-diketonate polymer). Nitrate esters, the peroxide explosive triacetone triperoxide, and the taggant 1,4-dimethyl-1,4-dinitrobutane were too strongly retained to elute from the La(dihed) column; however, these compounds could be eluted from the less retentive Cu(dihed) or Zn(dihed) columns. A Kováts index of 2124 for 2,4,6-trinitrotoluene (TNT) on the La(dihed) column compared to 1662 on the control illustrates the excellent discrimination against nonpolar hydrocarbons, the principal matrix interference expected in air samples. A proof-of-principle experiment demonstrated analysis of an extrapolated 47 part-per-trillion (ppt) (v/v) of TNT in an air extract concentrate.