To discuss the disadvantages or advantages of QuEChERS, you need to compare it with other technologies. We believe that the advantages of QuEChERS are obtained by comparing with other methods in many laboratories, and its shortcomings are more from personal preferences. The so-called shortcomings are not from their inherent defects. QuEChERS has undoubtedly changed the method of sample processing in pesticide residue analysis. Even those laboratories that do not use QuEChERS will use centrifuge tube extraction or dispersion matrix extraction in their methods.
Detection limit
There is another issue of note. Before the emergence of QuEChERS, the extraction solution obtained by the pesticide residue detection method generally contains 2-5g of sample per milliliter of non-polar solvent. At this time, when GC / MS (SIM mode) is used for splitless injection, the injection volume is 1 to 3 µL, and the method detection limit is generally 10 ng/g. Now unless the tester concentrates the extraction solution again, or perhaps replaces the solvent, the general QuEChERS method produces the extraction solution in acetonitrile, which is equivalent to the only 1g of sample per ml. In order to enable it to reach the detection limit of the previous method, programmable temperature vaporization (PTV) combined with large-volume injection (LVI) of 3 to 10 µL is required.
There is another issue of note. Before the emergence of QuEChERS, the extraction solution obtained by the pesticide residue detection method generally contains 2-5g of sample per milliliter of non-polar solvent. At this time, when GC / MS (SIM mode) is used for splitless injection, the injection volume is 1 to 3 µL, and the method detection limit is generally 10 ng/g. Now unless the tester concentrates the extraction solution again, or perhaps replaces the solvent, the general QuEChERS method produces the extraction solution in acetonitrile, which is equivalent to the only 1g of sample per ml. In order to enable it to reach the detection limit of the previous method, programmable temperature vaporization (PTV) combined with large-volume injection (LVI) of 3 to 10 µL is required.
The high cost of acetonitrile
In addition, acetonitrile is a good solvent for liquid-phase methods, but completely different for gas-phase. The use of PTV-LVI can reduce the amount of solvent entering the gas chromatography column. Therefore, if the appropriate method can be used, the use of acetonitrile will not be a disadvantage for the gas phase, but acidification of acetonitrile requires care-there are some sensitive pesticide residues will degrade in acetonitrile (perhaps at least in some batches of solvents), for which we can improve the stability of such pesticide residues by acidifying acetonitrile, but there are reports showing that it can increase column loss. Acetonitrile is more expensive than other solvents, but the QuEChERS method requires only 10 to 15 ml of acetonitrile per sample.
In addition, acetonitrile is a good solvent for liquid-phase methods, but completely different for gas-phase. The use of PTV-LVI can reduce the amount of solvent entering the gas chromatography column. Therefore, if the appropriate method can be used, the use of acetonitrile will not be a disadvantage for the gas phase, but acidification of acetonitrile requires care-there are some sensitive pesticide residues will degrade in acetonitrile (perhaps at least in some batches of solvents), for which we can improve the stability of such pesticide residues by acidifying acetonitrile, but there are reports showing that it can increase column loss. Acetonitrile is more expensive than other solvents, but the QuEChERS method requires only 10 to 15 ml of acetonitrile per sample.
Chlorophyll interference
Chlorophyll interference may be a potential disadvantage because even if 7.5mg GCB or 50mg ChloroFiltr adsorbent is added to each milliliter of extract, the removal rate is only 80 to 90%. For the removal of such macromolecular impurities, gel chromatography GPC has a better extraction effect than the dispersion matrix, but GPC has obvious disadvantages in terms of time, instrument cost, and reagent usage. Moreover, in the removal of fat macromolecules, the dispersion matrix extraction using C18 filler may be comparable to GPC in the freezing effect.
Chlorophyll interference may be a potential disadvantage because even if 7.5mg GCB or 50mg ChloroFiltr adsorbent is added to each milliliter of extract, the removal rate is only 80 to 90%. For the removal of such macromolecular impurities, gel chromatography GPC has a better extraction effect than the dispersion matrix, but GPC has obvious disadvantages in terms of time, instrument cost, and reagent usage. Moreover, in the removal of fat macromolecules, the dispersion matrix extraction using C18 filler may be comparable to GPC in the freezing effect.
Liquid phase analysis
The biggest problem mainly comes from liquid phase analysis. When the ionization method is API, the ionization of the analyte will be suppressed by the impurities flowing out at the same time. Most foods do not have this problem when using QuEChERS for sample processing; but for other more complex samples, we do not know whether QuEChERS will be more suitable than other methods. Current mass spectrometry has greatly improved sensitivity, and better ion source design can minimize the occurrence of such problems, but the competition between charges during ionization is an inherent characteristic of API, which is inevitable. The isotope internal standard is not suitable for all analytes, so the inspector has to evaluate the matrix effect, and the quantitative results of LC-API-MS can only be treated with caution before finding a solution.
The biggest problem mainly comes from liquid phase analysis. When the ionization method is API, the ionization of the analyte will be suppressed by the impurities flowing out at the same time. Most foods do not have this problem when using QuEChERS for sample processing; but for other more complex samples, we do not know whether QuEChERS will be more suitable than other methods. Current mass spectrometry has greatly improved sensitivity, and better ion source design can minimize the occurrence of such problems, but the competition between charges during ionization is an inherent characteristic of API, which is inevitable. The isotope internal standard is not suitable for all analytes, so the inspector has to evaluate the matrix effect, and the quantitative results of LC-API-MS can only be treated with caution before finding a solution.
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