Sample Preparation Methods For Svocs And Nvocs

Food matrixes encompass a broad range of physical types and the selection of a sample preparation method is, in first instance, dictated by the sample structure, e.g., powders, vegetables, fruits, meat and fatty or non-fatty beverages (e.g., milk and yoghurt versus soft drinks and wines). With the exception of food samples directly soluble in an organic solvent, e.g., vegetable oils, all samples analysed for

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Figure 4 Headspace sampling of fragrances by SHS (A) and HSSE (B). A sample of 100 mg was placed in a 20-mL headspace vial. Two internal standards (1,4-dibromobenzene and 4,4-dibromobiphenyl) were added at the 10ppm level. The SHS conditions were sample conditioning at 80°C for 15 min, HS needle at 90°C and injection of 1 mL at 350 mL/s with a 1/10 split ratio. For HSSE, the sample was conditioned at 80°C for 15 min with a 10 mm x 0.5 mm df PDMS Twister (Gerstel, Mulheim a/D Ruhr, Germany). The Twister was desorbed at 250°C during 10 min in the splitless mode and the released solutes were cryo-focussed at -100°C. The PTV injector was heated from -100°C at 600°C/min to 250°C and the split ratio was 1/10. The analyses were performed on an Agilent 6890 GC — 5975 MSD combination equipped with a 30-m L x 0.25-mm ID x 0.25 mm df HP-5MS (Agilent Technologies). The carrier gas was helium at 168 kPa constant pressure. Injection was at 250°C with a 1/10 split. The oven was programmed from 50°C, 1 min, at 8°C/min to 270°C. The MSD transfer line was at 250°C. The MS was operated in the scan mode between 40 and 350 amu.

NVOCs or SVOCs require a solvent extraction step to enrich/isolate the target solutes from the matrix. Extraction is commonly followed by a clean-up or fractionation step to selectively remove interferences that disturb the chromato-graphic analysis. However in recent years, the selective nature of mass spectrometers and especially of MS-MS techniques, is more and more exploited to eliminate or reduce these steps. However, care should be taken because these interferences can have a pronounced effect on the MS ionization efficiencies and isotope dilution should be applied.

Because both solid and liquid samples require enrichment in an organic solvent, it seems logical to discuss first the sample preparation techniques for solid and semi-solid samples and later those for liquid samples.

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