The FDA is responsible for regulation of dietary supplements as foodstuffs through the 1994 Dietary Supplement Health and
Education Act (DSHEA) amendment to the Food Drug and Cosmetic Act (FDCA). Product standardized practices were set, but compliance
was voluntary and no legal requirement existed for manufacturers. Due to public and industry concern, in 2003, the FDA proposed
requiring dietary supplement manufacturing to adhere to current good manufacturing practices (cGMPs). The final rule was issued
in June 2007 and is in full effect June 2010 (1). Basic GMPs require implementing comprehensive procedures to ensure product
quality and safety. Because many dietary supplements are largely derived from botanical sources, they must be tested for pesticide
contaminants in order to meet cGMP regulations. As a result of this requirement, labs are working to develop and validate
methods, an endeavor that is complicated by the wide range of pesticides and matrices to be tested.
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Although other researchers have used established methods like those found in the FDA Pesticide Analytical Manual (PAM) (2)
as an alternative, we developed a QuEChERS (quick, easy, cheap, effective, rugged, and safe)-based method for analyzing pesticides
in dietary supplements. QuEChERS is an approach developed by Anastassiades and colleagues (3) as a simple, rapid, effective,
yet inexpensive way to extract pesticide residues from fruits and vegetables, followed by a novel dispersive solid-phase extraction
(dSPE) cleanup of the extract. Because of these benefits, the approach has become popular and has been expanded to include
numerous other matrices. We chose QuEChERS as an alternative to PAM-based methods because of its speed, simplicity, and low
solvent use, as well as its ability to produce good extraction efficiencies for relatively polar pesticides (3).
Experimental
Chemicals and materials: QuEChERS extraction and dSPE tubes, QuEChERS internal and quality control standards, and cartridge SPE tubes (cSPE) were from
Restek Corporation (Bellefonte, Pennsylvania). The 46-pesticide mix, representing different chemical classes that have been
reported previously in dietary supplements (4–6), was a custom standard produced by Restek Analytical Reference Materials
group (Bellefonte, Pennsylvania). Sample preparation:
Sample wetting: Typically, QuEChERS methods use 10–15 g of material and are ideal for commodities with high water content (>80%). Therefore,
to prepare for a QuEChERS extraction with a dry commodity, it is critical to use a reduced amount of material and wet it with
water prior to extraction. In this work, 1 g of dietary supplement powder was combined with 9 mL of water. After shaking to
mix well, the wetted supplement was fortified with 200 μL of a 2 ng/μL pesticides spiking solution resulting in a 400-ng/g
spike level, relative to the original commodity. Also, 100 μL of QuEChERS Internal Standard Mix for GC–MS analysis was added.
The sample was allowed to soak for 2 h.
QuEChERS extraction: The EN 15662 QuEChERS method was used for sample extraction (7). A 10-mL volume of acetonitrile was added to the wetted sample.
After a 1-min shake, buffering extraction salts (Q-sep Q110, Restek) containing 4 g magnesium sulfate, 1 g sodium chloride,
1 g trisodium citrate dihydrate, and 0.5 g disodium hydrogen citrate sesquihydrate were added. Following another 1-min shake,
the sample was centrifuged for 5 min at 3000 U/min with a centrifuge (Q-sep 3000, Restek). Lastly, 5 μL of a quality control
standard containing anthracene was added to a 1-mL aliquot of extract to monitor for potential losses of planar compounds
to a graphitized carbon black during cleanup.
Extract cleanup: Based upon preliminary studies, we knew that while the extraction part of QuEChERS would be successful, the dSPE cleanup
step probably did not have the capacity to handle the matrix complexity and amount of most dietary supplements. Thus, we compared
dSPE to a cSPE cleanup and established a procedure that uses a QuEChERS extraction, cSPE cleanup, and GC–TOF-MS for determinations
of 46 pesticides in dandelion root powder.
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