SAMPLE CLEANUP continued
processes used to produce the oil. Traditionally, GPC and normal-phase SPE have been used in the cleanup of these samples for the analysis of PAHs. A new method uses a dual-layer SPE cartridge containing zirconia- coated silica for the extraction of PAHs from olive oil.5
The cartridge is
constructed of two beds of sorbent, with the top consisting of synthetic magnesium silicate (Florisil) and the bottom a mixture of Z-Sep/C18 (the same used in the QuEChERS cleanup method for olives). This method combines the extraction and cleanup steps, and produces an extract that can be analyzed by HPLC or GC. The cartridge is first conditioned with acetone and dried, followed by direct loading of the undiluted oil sample. Acetonitrile is used to elute the analytes, with fatty matrix remaining behind on the sorbents. The resulting eluent is then concen- trated to the appropriate final volume for chromatographic analysis. This method was applied to the analysis of PAHs from olive oil samples spiked at 2 ng/g. GC/MS background was low enough to detect all PAHs on a single-quadrupole GC/MS system operated in SIM mode. Table 1 shows a summary of the average recoveries, after blank subtraction, for spiked replicates. Reproducibility is indicated as %RSD. All PAHs except naph- thalene had recoveries of greater than 80%. The reason for the lower naphthalene recovery was most likely due to evaporative losses while
Table 1 – Recoveries of PAHs from olive oil spiked at 2 ng/g and extracted by direct SPE using dual-layer cartridge containing zirconia-base sorbent
Naphthalene Acenaphthene Acenaphthylene Fluorene
Phenanthrene Anthracene Fluoranthene Pyrene
Benzo[a]anthracene Chrysene
Benzo[b]fluoranthene Benzo[k]fluoranthene Benzo[a]pyrene
Indeno[1,2,3-cd]pyrene Dibenz[a,h]anthracene Benzo[g,h,i]perylene
%Recovery %RSD (n = 4) 63 96 95
12 4
119 154 99
100 99 98 98 94 95 86 85 94 82
12 15 49 8 6 6 7 9 5 2 3 2
10 4
Conclusion When analyzing PAHs and pesticides in fatty samples, fatty matrix is often
coextracted along with the compounds of interest. Because this can cause problems in the chromatographic analysis, such as system contamination and fouling, and ion suppression in LC/MS, cleanup is essential. Zirconia- based sorbent can be used to remove fatty acids, mono- and diglycerides, as well as some pigmentation. The sorbent can be used by itself or com- bined with C18 to retain a wider range of fats.
Used successfully in place of PSA/C18 for cleanup as part of the QuEChERS method, zirconia-based sorbents offer lower background and higher re- coveries for some compounds. They have also been used in combination with synthetic magnesium sulfate and C18 in a dual-layer SPE cartridge that can be applied for the direct extraction of PAHs from olive oil. This cartridge offers an easier, more economical alternative to GPC and nor- mal-phase SPE for the extraction of nonpolar contaminants from edible oil samples.
References 1. EU Commission Regulation No 835/2011. Official Journal of the Euro-
pean Union, Aug 20, 2011, 215, 4–8.
2. National Standards of People’s Republic of China, GB 2716-2005: Hygienic Standard for Edible Vegetable Oil. Issued 1/25/2005. Ministry of Health of the People’s Republic of China, Standardization Adminis- tration of the People’s Republic of China.
3. AOAC Official Method 2007.01, Pesticide Residues in Foods by Aceto- nitrile Extraction and Partitioning with Magnesium Sulfate.
4. Sapozhnikova, Y. and Lehotay, S.J. Multi-class, multi-residue analysis of pesticides, polychlorinated biphenyl, polycyclic aromatic hydrocar- bons, polybrominated biphenyl ethers and novel flame retardants in fish using fast, low-pressure gas chromatography-tandem mass spec- trometry. Anal. Chim. Acta 2013, 758, 80–92.
5. Stenerson, K.K.; Shimelis, O. et al. Analysis of polynuclear aromatic hydrocarbons in olive oil after solid-phase extraction using a dual- layer sorbent cartridge followed by high-performance liquid chroma- tography with fluorescence detection. J. Agric. Food Chem. 2015, 63, 4933–9.
Katherine K. Stenerson is principal scientist; Michael Ye is senior manager, Research & Development; Olga Shimelis is principal scientist/R&D supervisor; Emily Barrey is senior scientist; and Michael Halpenny is research and develop- ment technician, MilliporeSigma/Supelco, 595 Harrison Rd., Bellefonte, Penn. 16823, U.S.A.; tel.: 814-359-5781; e-mail:
katherine.stenerson@
sial.com; www.
sigmaaldrich.com
AMERICAN LABORATORY 34 APRIL 2016
concentrating the samples. Values for %RSD were less than 15% for all PAHs except phenanthrene. This PAH was detected in the unspiked olive oil, and despite blank subtraction, its presence affected results.
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