Another cup of PAH tea please!

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!

Figure 1: A modified QuEChERS extraction was used for the analysis of PAHs in tea. We also used this extraction method for PAHs in mussels.

Figure 1: A modified QuEChERS extraction was used for the analysis of PAHs in tea. We also used this extraction method for PAHs in mussels.

Figure 2:  The silica SPE cleanup procedure removed the large amount of chlorophyll in the Dragonwell tea extract.  Chlorophyll is nonvolatile and can quickly degrade the GC inlet performance.

Figure 2: The silica SPE cleanup procedure removed the large amount of chlorophyll in the Dragon Well tea extract. Chlorophyll is nonvolatile and can quickly degrade the GC inlet performance.

Figure 3: Coupling the Rxi-PAH with a fast modulation time maintains separation of isobaric PAHs in the first dimension.

Figure 3: Coupling the Rxi-PAH with a fast modulation time maintains separation of isobaric PAHs in the first dimension.

Figure 4:  Separation of closely eluting benzo fluoranthenes are baseline separated on the Rxi-PAH column.

Figure 4: Benzo[b]fluoranthene, benzo[k]fluoranthene and benzo[j]fluoranthene are all baseline separated in the first dimension using the Rxi-PAH column.  This separation is maintained in the GCxGC system using a fast (1.5 sec) modulation period. 

Table I: Incurred PAHs found in the Dragonwell Tea.  The red dot signifies the EFSA PAH4.

Table I: Incurred PAHs found in the Dragon Well tea. The red dot signifies the EFSA PAH4.

One Response to “Another cup of PAH tea please!”

  1. Jason Hoisington says:

    Do you have any plans to test tea after it has been brewed? I’d be curious to see how the contaminants extract after steeping, since most people don’t eat the tea leaves. Also, I seem to recall that PAHs in water tend to adsorb and settle out on solid particles. An argument for using a finer mesh tea strainer perhaps?

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