It seemed not too long ago that Julie Kowalski and I were analyzing tea, a lot of tea, and only tea. To this day we cringe at the thought of tea, but hopefully our pain can be your gain. We analyzed pesticides, natural products, and polycyclic aromatic hydrocarbons (PAHs) in tea. Julie and Amanda Rigdon first started analyzing PAHs in Yerba Mate tea and found quite high levels of PAHs due to the roasting process. This spurred more research into other teas that also have a roasting pretreatment. Longjing tea, also known as Dragon Well tea, has a very specific hand roasting process that involves pan frying the leaves just after harvest.
Amanda and Julie put in a lot of work developing the sample preparation method for analyzing PAHs in tea. The procedure is below in Figures 1 and 2. After the QuEChERS extraction and silica SPE cleanup the extracts were analyzed by GCxGC-TOFMS. We used a 60 m x 0.25 mm x 0.10 µm Rxi-PAH column in the first dimension and a 1 m x 0.25 mm x 0.10 µm Rxi-1HT in the second dimension. Since many PAHs are isobaric, chromatographic separation is necessary. With a GCxGC setup, it is important to preserve the first dimension separation by matching the modulation period for 3-4 slices across the peak. We chose a 1.5 sec modulation period in order to maintain the separation of closely eluting chrysene and triphenylene and also the benzo fluranthenes (Figures 3 and 4).
We did find ppb levels of PAHs in the Dragon Well tea that we analyzed, including those PAHs in the European Food Safety Authority (EFSA) priority 4 list (Table I). Surprisingly, I still enjoy drinking tea, even though I really don’t want to analyze that very complex matrix again!