What Is Clean Up In Pah Sample

Concern well-nigh pesticide residues and polynuclear effluvious hydrocarbons (PAHs) in food has led to the regulation of maximum contaminant levels,^ane,ii and highlighted the need for more than sensitive and selective testing methodologies that apply gas chromatography/mass spectrometry (GC/MS) and liquid chromatography/mass spectrometry (LC/MS). Since samples cannot be injected straight into these instruments, sample preparation and cleanup methods are needed.

Fat-containing samples are a special challenge in the analysis of PAHs and pesticides. These compounds that are often found in the fatty portion of samples, and methods to extract them, usually coextract fatty. If not removed from the final sample excerpt, fatty materials tin interfere with the chromatographic analysis and/or contaminate instrumentation.

Fatty groundwork can cause interferences in GC/MS and LC/MS analyses, and contaminate GC inlets and columns, resulting in active sites, which reduce the responses of some compounds. In LC, analytical columns with a buildup of fatty groundwork must be done extensively. Increased background tin foul GC/MS and LC/MS detectors, resulting in significant downtime for maintenance and cleaning.

Cleanup approaches include the apply of C18 sorbent as office of the QuEChERS (quick, like shooting fish in a barrel, cheap, constructive, rugged and safe) method, gel permeation chromatography (GPC) and solid-phase extraction (SPE) with normal-phase sorbents such as silica or alumina gel. While GPC is effective, it requires special instrumentation; normal-phase SPE often uses very large columns and substantial amounts of solvent.

An culling cleanup method employs zirconia-based sorbents. Zirconia acts as a Lewis acid, interacting with compounds that are electron donors (i.e., Lewis bases). In fats, this includes phospholipids and the hydroxyl groups present on fatty acids, monoglycerides and diglycerides. Z-Sep sorbents (MilliporeSigma/Supelco, Bellefonte, Penn.) are offered in iii formulations: a zirconia-coated silica (Z-Sep), zirconia-coated silica blended with a C18 functionalized silica (Z-Sep/C18) and single silica-based material functionalized with both C18 and zirconia (Z-Sep+). The C18 offers additional selectivity for fat removal past providing retention through hydrophobic interactions, interacting with triglycerides through the alkyl chains in their structures. In the Z-Sep/C18 and Z-Sep+ sorbents, the zirconia and C18 chemistries together produce a synergistic effect to retain the fatty constituents nowadays in food samples.

Applications using zirconia-based sorbents for QuEChERS

QuEChERS extraction was originally developed to analyze pesticide residues in fruits and vegetables³ every bit well equally other classes of compounds and foods.⁴ Acetonitrile extraction is followed by a salting-out step. The resulting excerpt can exist subjected to cleanup using different sorbents. As shown below, the zirconia sorbents were compared to common nonzirconia- based sorbents as part of the QuEChERS method: pesticides from olives, pesticides from avocado and PAHs from grilled hamburger.

Pesticides from olives. Canned olives containing approximately fifteen% fatty were spiked with pesticides at 50 ng/g and extracted using QuEChERS. The extract was so cleaned with unlike sorbents: primary secondary amine (PSA), PSA/C18 and Z-Sep/C18. PSA removes acidic interferences and some sugars and is often used with C18 for cleanup. Final assay was performed by LC/MS/MS. Figure 1 shows a comparison of the average pesticide recoveries obtained for spiked replicates subsequently cleanup with the unlike sorbents. Average recoveries after Z-Sep/C18 cleanup were similar or better than the other two sorbents. Fenhexamide, anilazine and sethoxydim showed significantly better recoveries using Z-Sep/C18 cleanup. This was due to lower background and later on less ion suppression in the LC/MS assay.

Figure 1 – Comparison of boilerplate recoveries of pesticides from olives after QuEChERS cleanup with different sorbents; spiking level of 50 ng/g.

Pesticides in avocados. Avocado contains x–xv% fat; in this application, several unlike classes of pesticides, including organochlorine, organophosphorus and pyrethoid, were extracted from spiked samples and analyzed on a single-quadrupole GC/MS operated in selected ion fashion (SIM). Homogenized avocado was spiked at 20 ng/k with pesticides and extracted past QuEChERS. For cleanup, three sorbents were evaluated: 1) PSA/C18, 2) Z-Sep+ and 3) Z-Sep+/PSA. Z-Sep+ differs from the Z-Sep/ C18 alloy in that the zirconia and C18 are bonded on the same silica particle. The 3rd sorbent mixture was created for this application to determine if addition of PSA offered farther background reduction over Z-Sep+ alone. Boilerplate recoveries from spiked replicates (n = 3) are shown in Figure 2. Recoveries of many pesticides were highest subsequently Z-Sep+ only cleanup, and the improver of PSA to the Z-Sep+ actually reduced recoveries. The lowest recoveries were obtained after cleanup with PSA/C18, and these extracts also showed college background. In the case of the tardily-eluting pyrethroid pesticides cypermethrin and deltamethrin, high background obscured detection altogether. In improver, PSA/C18 reduced recoveries of some of the more than hydrophobic organochlorine pesticides such every bit 4,4'-DDT and methoxychlor.

Figure 2 – Comparing of boilerplate recoveries of pesticides from avocado after QuEChERS cleanup with dissimilar sorbents; spiking level of 20 ng/g.

Performance of the sorbents for removing groundwork was compared by gravimetric conclusion of the amount of residuum remaining subsequently cleanup of extracts prepared from equal weights of avocado (Figure 3). Compared to no cleanup, the extract cleaned with Z-Sep+ had the everyman weight of rest remaining, indicating that this sorbent retained the greatest amount of background.

Effigy three – Comparison of residue remaining from avocado extracts subsequently QuEChERS cleanup with different sorbents.

PAHs in grilled hamburger. PAHs are formed when fat contacts high-temperature sources such as hot dress-down. Hamburger that independent 25% fat prior to cooking was grilled to well-done over an open flame. Information technology was then homogenized and spiked at 100 ng/m with a variety of PAHs with two–6 rings in their structures. Sample was also reserved for testing without spiking, and was used for blank subtraction to determine recoveries. After QuEChERS extraction, the samples were cleaned with 4 sorbents: 1) Z-Sep (zirconia-coated silica without C18), 2) Z-Sep+, 3) Z-Sep+/PSA and iv) PSA/C18. Due to the hydrophobicity of PAHs, Z-Sep alone was included to evaluate if better recoveries could exist obtained with a sorbent that does not contain C18. Samples were analyzed by GC/MS-SIM; the boilerplate recoveries for due north = three spiked replicates (after blank subtraction) are shown in Figure iv. PAHs are listed on the 10-centrality in gild of increasing size and hydrophobicity. Reproducibility for the set of spikes was very good for all cleanups, with %RSD values less than 10% for all but one chemical compound. The difference in the operation of the sorbents is evident when comparing the heavier PAHs. Recoveries of the five- and six-ring PAHs were the highest after Z-Sep-only cleanup. Z-Sep is the simply sorbent that did non comprise C18, indicating that the presence of C18 decreased recoveries for the heavier compounds. In addition, although not shown hither, the Z-Sep cleaned extracts showed the everyman background by GC-MS.

Figure 4 – Comparison of average recoveries of PAHs from grilled hamburger after QuEChERS cleanup with different sorbents; spiking level of 100 ng/g.

Utilise of zirconia-based sorbent in SPE

Analysis of PAHs from olive oil. Olive oil can become contaminated with PAHs through environmental exposure of the fruit and manufacturing processes used to produce the oil. Traditionally, GPC and normal-stage SPE have been used in the cleanup of these samples for the assay 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 constructed magnesium silicate (Florisil) and the bottom a mixture of Z-Sep/C18 (the aforementioned used in the QuEChERS cleanup method for olives). This method combines the extraction and cleanup steps, and produces an extract that tin exist analyzed by HPLC or GC. The cartridge is commencement conditioned with acetone and dried, followed by direct loading of the undiluted oil sample. Acetonitrile is used to elute the analytes, with fat matrix remaining behind on the sorbents. The resulting eluent is and then concentrated to the appropriate final volume for chromatographic analysis. This method was applied to the assay of PAHs from olive oil samples spiked at 2 ng/g. GC/MS background was low enough to observe all PAHs on a single-quadrupole GC/MS system operated in SIM style. Table ane shows a summary of the average recoveries, after blank subtraction, for spiked replicates. Reproducibility is indicated as %RSD. All PAHs except naphthalene had recoveries of greater than 80%. The reason for the lower naphthalene recovery was well-nigh likely due to evaporative losses while 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.

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

Conclusion

When analyzing PAHs and pesticides in fatty samples, fatty matrix is oftentimes coextracted forth with the compounds of interest. Because this can cause problems in the chromatographic analysis, such equally organisation contamination and fouling, and ion suppression in LC/MS, cleanup is essential. Zirconia-based sorbent tin can be used to remove fatty acids, mono- and diglycerides, besides equally some pigmentation. The sorbent can exist used by itself or combined with C18 to retain a wider range of fats.

Used successfully in identify of PSA/C18 for cleanup every bit part of the QuEChERS method, zirconia-based sorbents offering lower background and college recoveries for some compounds. They take also been used in combination with constructed magnesium sulfate and C18 in a dual-layer SPE cartridge that can exist applied for the straight extraction of PAHs from olive oil. This cartridge offers an easier, more economical culling to GPC and normal- stage SPE for the extraction of nonpolar contaminants from edible oil samples.

References

1. EU Commission Regulation No 835/2011. Official Journal of the European Union, Aug 20, 2011, 215, 4–8.
2. National Standards of People's Democracy of China, GB 2716-2005: Hygienic Standard for Edible Vegetable Oil. Issued one/25/2005. Ministry of Health of the People'due south Commonwealth of China, Standardization Administration of the People'southward Republic of China.
3. AOAC Official Method 2007.01, Pesticide Residues in Foods by Acetonitrile Extraction and Division with Magnesium Sulfate.
4. Sapozhnikova, Y. and Lehotay, Due south.J. Multi-class, multi-residue analysis of pesticides, polychlorinated biphenyl, polycyclic effluvious hydrocarbons, polybrominated biphenyl ethers and novel flame retardants in fish using fast, low-pressure gas chromatography-tandem mass spectrometry. Anal. Chim. Acta 2013, 758, 80–92.
5. Stenerson, K.K.; Shimelis, O. et al. Analysis of polynuclear effluvious hydrocarbons in olive oil after solid-phase extraction using a duallayer sorbent cartridge followed by high-performance liquid chromatography with fluorescence detection. J. Agric. Food Chem. 2015, 63, 4933–nine.

Katherine Thousand. Stenerson is principal scientist; Michael Ye is senior managing director, Research & Evolution; Olga Shimelis is principal scientist/R&D supervisor; Emily Barrey is senior scientist; and Michael Halpenny is research and development technician, MilliporeSigma/Supelco, 595 Harrison Rd., Bellefonte, Penn. 16823, United states of americaA.; tel.: 814-359-5781; e-mail: [email protected]; world wide web.sigmaaldrich.com

Source: http://www.americanlaboratory.com/914-Application-Notes/185012-Sample-Cleanup-for-the-Analysis-of-Pesticide-Residues-and-Polynuclear-Aromatic-Hydrocarbons-in-Fatty-Food-Matrices/

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