Application of a direct immersion.stir bar sorptive extraction (DI.SBSE)combined GC.MS method for fingerprinting alkylpyrazines in tea and tea.like infusions

A series of alkylpyrazines, contributing to the overall flavor, are described in tea and tea infusions. Their low concentrations and moderate water solubility are facing analytical trouble when it comes to typical applied headspace analyses. Accordingly, a stir bar sorptive extraction methodology (SBSE)was established. It was found that immersion-based techniques (direct-immersion SBSE (DI-SBSE)and multiple SBSE (mSBSE)) showed higher extraction efficiency compared to headspace sorptive extraction (HSSE). In the end, a DI-SBSE methodology was established with a calibration range of 0.1-50 µg/L for six alkylpyrazines to systematically quantify their presence in tea and tea-like infusions. With determined LOQs between 21 and 118 ng/L, the method was sensitive enough to detect the expected low amounts. Application of the established DI-SBSE methodology for six alkylpyrazines in seven green, three white, one oolong, two black teas, as well as two tea-like infusions (nettle and raspberry leaf)revealed great variations in total concentration of alkylpyrazines between 0.36?±?0.05 µg/L (raspberry leaf)and 24.20?±?0.41 µg/L (oolong tea). Furthermore, concentration levels in between the same tea type ranged drastically, with 14.19?±?0.62 µg/L for Longjing green tea and 0.74?±?0.02 µg/L for Warwick green tea. Most abundant alkylpyrazines in the samples were 2-methylpyrazine and 2,5-dimethylpyrazine. Overall good similarities in compositional distribution of alkylpyrazines in the same tea type and strong correlations of the alkylpyrazines over all types indicating distinct fingerprints being present and the types are differentiable based on their alkylpyrazine pattern.