OPTIMIZING SPLIT SPLITLESS INJECTION PORT PARAMETERS FOR SOLID-PHASE MICROEXTRACTION/

Desorption profiles of analytes using a conventional split/splitless i njection port after solid-phase microextraction were determined in rea l-time by direct coupling of the injection port to a mass spectrometer . Desorption times for aromatic hydrocarbons increased with the analyt e's boiling point, and decreased with injection port temperature. For example, naphthalene (b.p. 218 degrees C) was efficiently desorbed in <12 s at 200 degrees C and higher temperatures, while benz[a]anthracen e required >60 s at 200 degrees C, but only 15 s at 300 degrees C. As expected, desorption profiles from a 7-mu m poly(dimethylsiloxane) fib er were initially narrower than the 100-mu m fiber; however, the profi les from the 7-mu m fiber showed significantly more tailing indicating the presence of more available active sites (possibly on the silica c ore) for thinner fiber coatings. All desorption profiles were wider th an could be accepted for capillary GC, but good chromatographic peak s hapes were obtained by cryogenic focusing in the GC column, increasing the GC column film thickness, and reducing the injection port liner v olume from 1 ml to 0.25 ml.