Detectability enhancement by the use of large-volume injections in gas chromatography-cryotrapping-Fourier transform infrared spectrometry.

The use of large-volume injections via a loop-type interface in GC-cryotrapping-FT-IR has been studied. n-Alkanes and polycyclic aromatic hydrocarbons (PAHs) were used as test compounds. When using 100-μl injections the analyte detectability was enhanced by two to three orders of magnitude compared with conventional split/splitless injections. For the alkanes, the absolute detection limits were nearly independent of the injected volume and the mode of injection. With the PAHs a water background (due to press-fit connections and six-port valves) somewhat disturbed the GC-FT-IR chromatograms and the spectra of the PAHs. This detracts from the system performance. Still, upon going from split/splitless injections to 100-200 μl injections, analyte detectability was increased by a factor of 30-500. The repeatability of the total 100-μl GC-cryotrapping-FT-IR procedure was satisfactory. The potential of the set-up was demonstrated by determining PAHs in river water at the 0.5 μg/l level by means of 'micro' liquid-liquid extraction and 100-μl GC-cryotrapping-FT-IR. The FT-IR spectra obtained matched well with those of standard libraries.