| Direct immersion solid-phase microextraction was used to analyze pyrazine standards from water. Optimal experimental conditions were established by studying the effects of various parameters. The fiber coated with Carboxen/polydimethylsiloxane gave better extraction results than the polydimethylsiloxane fiber. Adsorption profiles of the tested pyrazines were obtained and adsorption time was established as 15 minutes. Basic pH, higher temperature and salt addition favored the adsorption. The developed SPME method was further validated. The calibration curves for the tested pyrazine standards showed linearity in the range of 10 to 10,000 ppb (10 to 10,000 ng/mL), with detection limits of 23 to 950 ppb. Quantitative reproducibilities (relative standard deviations) were in the range of 3.5% to 10.0% except for acetylpyrazine which was 23.7%.;The optimized SPME method was successfully applied to analyze volatile compounds in Maillard model reaction systems consisting of glucose and different amino acids. The solutions of glucose and amino acids (pH 8.0) were heated at 180°C for 2 h. Experimental results showed that among the tested amino acids, aspartic acid exhibited the highest reactivity, whereas proline exhibited the lowest reactivity. The reactivity order from the highest to the lowest was: Asp > Asn > Glu > Gln > Ala > Lys > Gly > Ser > Pro. In reactions involving the combination of different amino acids, it was found that there were three types of coexisting effects of the amino acids: activating, inhibiting and maintaining. Different volatile profiles were obtained from reactions of different amino acid or their combinations with glucose.;The reproducibility of SPME in analyzing volatile compounds in Maillard model reaction systems was proved to be good again. Finally, the SPME test results were compared to those obtained by solvent extraction and were found to be comparable to the latter. |
