Determination of vapor pressures for organophosphate esters

Organophosphate compounds are ubiquitous in the environment and to better understand and predict their environmental transport and fate, well-defined physical-chemical properties are needed. The subcooled liquid-phase vapor pressures at 298.15 K (p) were determined for 11 chlorinated and nonchlorinated phosphate flame retardants (PFRs) by the capillary gas chromatography retention time method (GC-RT). Values of log (p/Pa) ranged from -5.22 to -1.32 and enthalpies of vaporization (δ H/kJ·mol) ranged from 82.0 to 109. Log (p/Pa) by GC-RT showed good overall agreement with estimates using the Modified Grain Method (EpiSuite) and with the mean of experimental and in silico literature values, whereas values for the chlorinated PFRs appeared to be overestimated. SPARC modeling seriously underestimated p, especially for the less volatile compounds. The Junge-Pankow adsorption model at 288.15 K predicted that most of the PFRs would be predominantly in the particulate phase in urban air and distributed between the particulate and gaseous phases in background air.