Rapid headspace solid-phase microextraction-gas chromatographic-time-of-flight mass spectrometric method for qualitative profiling of ice wine volatile fraction. I. Method development and optimization.

An analytical method for the determination of volatile and semi-volatile compounds representing various chemical groups in ice wines was developed and optimized in the presented study. A combination of the fully automated solid-phase microextraction (SPME) sample preparation technique and gas chromatographic-mass spectrometric (GC-MS) system to perform the final chromatographic separation and identification of the analytes of interest was utilized. A time-of-flight mass spectrometric (TOF-MS) analyzer provided very rapid analysis of this relatively complex matrix. Full spectral information in the range of m/z 35-450 was collected across the short GC run (less than 5 min). Divinylbenzene/Carboxen/Polydimethylsiloxane (DVB/CAR/PDMS) 50/30 microm fiber performed best during the optimization experiments and it was used in the headspace SPME mode to isolate compounds from ice wine samples, consisting of 3 mL wine with 1g salt addition. After the sample incubation and extraction (both 5 min at 45 degrees C), analytes were thermally desorbed in the GC injector for 2 min (injector maintained at 260 degrees C) and transferred into the column. The MS data acquisition rate of 50 spectra/s was selected as optimal. The optimized analytical method did not exceed 20 min per sample, including both the isolation and pre-concentration of the analytes of interest, the final GC-TOF-MS analysis and the fiber bake-out. Both a linear temperature-programmed retention index (LTPRI) method using C(8)-C(20) alkanes loaded onto the fiber and a mass spectral library search were employed to identify the target compounds. The repeatability of the developed and optimized HS-SPME-GC-TOF-MS method for ice wine analysis, expressed as relative standard deviation (RSD, %, n=7), ranged from 3.2 to 9.0%.