"Just Enough" Sample Preparation: A Proven Trend in Sample Analysis - - Chromatography Online
"Just Enough" Sample Preparation: A Proven Trend in Sample Analysis

LCGC Europe
Volume 25, Issue 12, pp. 670-674

Figure 7: Flowchart of the QuEChERS AOAC sample preparation procedure. Adapted from reference 7.
QuEChERS (quick, easy, cheap, effective, rugged and safe) is a sample preparation technique that was originally developed for the extraction of pesticides from fruits and vegetables (4). It is a relatively simpler sample preparation procedure with two steps: a salting out partitioning extraction involving water and acetonitrile with high concentrations of salts such as sodium chloride, magnesium sulphate and buffering agents, and a dispersive-SPE step in which an aliquot from the first step is treated with various sorbents to remove matrix compounds that could interfere with subsequent LC–MS, LC–MS-MS, GC–MS or GC–MS-MS analysis. The technique has proven to be widely applicable at trace levels for hundreds of pesticides in a variety of matrices. Standard protocols are available that make it a generic sample preparation procedure.

Figure 8: Overlay HPLC–fluorescence chromatograms of a PAH-spiked fish extract. The black portion of the chromatogram used 260-nm and 352-nm excitation and emission wavelengths, respectively, the red portion used 260-nm and 420-nm wavelengths, and the blue portion used 260-nm and 440-nm wavelengths. For acenaphthylene, UV detection at 230-nm was used. Column: 50 mm 4.6 mm, 1.8-m dp Agilent Zorbax Eclipse PAH C18; flow rate: 0.8 mL/min; temperature: 18 C; injection volume: 5 L; mobile-phase A: deionized water; mobile-phase B: acetonitrile; gradient: 60% B for 1.5 min, 60–90% B in 6.5 min, 90–100% B in 6 min. Peaks: 1 = naphthalene (20 ng/g), 2 = acenaphthylene (20 ng/g), 3 = acenaphthene (10 ng/g), 4 = fluorene (10 ng/g), 5 = phenanthrene (10 ng/g), 6 = anthracene (10 ng/g), 7 = fluoranthene (10 ng/g), 8 = pyrene (10 ng/g), 9 = 1,2-benzanthracene (5 ng/g), 10 = chrysene (10 ng/g), 11 = benzo[e]pyrene (5 ng/g), 12 = benz[e]acenapthylene (5 ng/g), 13 = benzo[k]fluoranthene (5 ng/g), 14 = dibenz[a,h]anthracene (5 ng/g), 15 = benzo[ghi]perylene (5 ng/g), 16 = indeno[1,2,3-cd]pyrene (5 ng/g).
Recently, QuEChERS extraction has expanded well beyond the pesticide laboratory and has been used for many matrices ranging from antibiotics in meat and poultry, veterinary drugs in animal feed, and environmental contaminants in soil. In this example, using the protocol in Figure 7, QuEChERS was used for the extraction of polycyclic aromatic hydrocarbons (PAHs) in fish. The PAHs are a large group of organic compounds included in the European Union and the United States Environmental Protection Agency priority pollutant list because of their mutagenic and carcinogenic properties. In the marine environment, PAHs are bioavailable to marine species via the food chain, as waterborne compounds and contaminated sediments. This application shows that tandem MS detection techniques are not necessarily required for just enough sample preparation. Most of the PAHs are highly fluorescent and thus, as shown in Figure 8, reversedphase HPLC was combined with fluorescence detection to determine 16 of these compounds at a spiking level of less than 10 ng/g (5). QuEChERS extraction provided excellent recoveries with %RSDs below 2.


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