Determination of volatile alkylpyrazines in microbial samples using gas chromatography-mass spectrometry coupled with head space-solid phase microextraction

Background: Determination of volatile alkylpyrazines (VAPs) in microbial samples is needed for the understanding of microbial metabolism. An analytical method for screening and quantification of six volatile alkylpyrazines was developed and successfully applied to the real microbial samples. Methods: Headspace-solid phase microextraction (HS-SPME) which is a simple extraction simultaneously carrying out clean-up and pre-concentration of VAPs in microbial samples was adopted. GC-TOF/MS with CombiPal SPME autosampler was used for fast screening of microbial samples and the optimization of HS-SPME condition. Separation and quantification of six VAPs that have the potential to be detected in microbial samples using quadrupole GC/MS in chemical ionization (CI) mode were carried out. Results: The optimal extraction conditions for HS-SPME at 50 °C and 50 min were investigated. To eliminate matrix effects, DB-WAX column was more appropriate to separate each alkylpyrazines from the interferences than DB-5MS column. Chemical ionization provided enhanced confirmation from adduct ions ([M + 29]⁺ and [M + 41]⁺) of methane reagent gas as well as increasing signal intensity of molecular ions for quantitative analysis. Linear calibration curves of six alkylpyrazines were obtained within a range between 1 and 50 ng/g. Conclusions: This proposed method was successfully applied to the microbial samples. 2-Methylpyrazine and 2,5-dimethylpyrazine were determined in the level of 6.0~34.0 ng/g.