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By Jack Cochran, Julie Kowalski, and Amanda Rigdon
• Fast, simple modified QuEChERS extraction and silica cartridge SPE cleanup extend column lifetime and
reduces inlet maintenance.
• Novel Rxi®-PAH GC column selectivity ensures separation and accurate reporting of EFSA PAH4 and other key PAHs.
Traditionally, yerba mate tea, which is brewed from loose
Ilex para-
guariensis
leaves and stems, has been especially popular in Argentina,
Brazil, Paraguay, and Uruguay. More recently, the popularity and eco-
nomic importance of mate tea has grown worldwide, due in part to
its reputation of providing numerous health benefits. Unfortunately,
a high incidence of esophageal cancer has been found in populations
with high mate tea consumption, indicating a possible link between
mate tea and cancer [1,2]. Since mate tea contains relatively high lev-
els of toxic polycyclic aromatic hydrocarbons (PAHs), accurate analysis
of these compounds is becoming increasingly important. Currently,
monitoring efforts are focused on two analyte lists recommended
by the European Food Safety Authority (EFSA): EFSA PAH4 (benzo[a]
pyrene, chrysene, benz[a]anthracene, and benzo[b]fluoranthene) and
EFSA PAH8 (all PAH4 analytes plus benzo[k]fluoranthene, indeno[1,2,3-
cd]pyrene, dibenz[ah]anthracene, and benzo[ghi]perylene).
Due to the complexity of the botanical matrix, testing methods for
mate tea often use exhaustive sample preparation, including super-
critical fluid extraction, pressurized fluid extraction, and gel perme-
ation chromatography. In addition, isobaric compounds also make
PAH analysis difficult because, since isobars cannot be distinguished
by mass spectrometry, accurate reporting depends on being able
to obtain chromatographic separations. Given these challenges, our
goal was to develop a robust, yet simple, sample preparation method
for PAHs in tea. As shown here, we paired this sample preparation
approach with a highly selective GC column and both TOFMS and
MS/MS analyses to produce accurate quantitative data for critical
PAHs—including isobaric compounds—in a short analysis time.
Speedy Sample Preparation Saves Time and
Removes Matrix Interferences
QuEChERS sample preparation methods are a desirable alternative
because they are quick and easy, but still provide quality results. The
QuEChERS approach was originally designed for pesticide residues in
fruit and vegetables, but modifications such as those used here have
been developed to expand it beyond the original scope. Compounds
such as PAHs, veterinary drugs, and persistent organic pollutants have
been testing using QuEChERS methods in difficult commodities like
tea, spices, and tobacco. The procedure used here (see sidebar), was
much less time- and labor-intensive than traditional sample prepara-
tion methods for tea, and it effectively removed chlorophyll and other
nonvolatile materials that can quickly foul GC inlets and columns
(Figure 1). Not only was this approach fast and effective in removing
matrix interferences, but it also can save labs time and money by
reducing inlet maintenance and extending GC column lifetime.
Unique Rxi®-PAH Column Prevents Coelutions
and Ensures Accurate Reporting
An Rxi®-PAH column was chosen for this analysis because its novel
selectivity separates all priority compounds, including the EFSA
PAH4 subset as well as benzo [b], [k], and [j] fluoranthenes (Figure
1). During method development, accuracy was assessed based on
the recovery of 30 PAHs fortified at 500 ng/g in mate tea samples. In
addition, incurred PAH levels were determined in an unfortified tea
sample. Samples were analyzed by both GC-MS/MS and GC-TOFMS
and results using both techniques were quite similar for the EFSA
PAH4 compounds.
Overall, the modified QuEChERS method used here effectively pro-
duced good quantitative data for PAHs in mate teas. As shown in Table
I, satisfactory recoveries (72-130%) were obtained for the 500 ng/g
fortified sample and concentrations ranging from 7 ng/g to 540 ng/g
were determined in the unfortified sample. The selectivity of the Rxi®-
PAH column separated all isobars and allowed us to report accurate
values without bias from coeluting compounds. For example, this
method effectively separated triphenylene and chrysene, which are
New GC Method for Polycyclic Aromatic Compounds
in Yerba Mate Tea Combines Simplified Prep and Improved
Accuracy for EFSA PAH4 and EFSA PAH8 Compounds