QuEChERS FAQUnited Science
QuEChERS with CarbonX can streamline your workflow, reduce the number of preparation steps, reduce time required to evaporate, reduce maintenance costs, and improve calibration stability. In general, QuEChERS removes matrix and leaves the analyte in solution. Thus in your method development, you often can use it in combination with SPE and determinative steps to quantify multi-analytes.
2. How long does the QuEChERS procedure take?
The actual extraction and dSPE cleanup procedure should take no more than 90 minutes at the most for 25 to 30 samples. The time limiting step is the removal of toluene (if used).
3. When do I choose QuEChERS over SPE?
The QuEChERS method is applicable to your work if you are interested in eliminating matrix interferences. This technique works particularly well for solids, semi-solids, viscous liquid mixtures, and small volumes of liquid samples.
4. How much does United Science compare to other vendors in terms of cost?
We are priced at market prices. You will pay no more for our all our benefits, cost savings, time savings. It all adds up to a whopping deal. You can learn more by visiting our QuEChERS page. A sample typically costs a few dollars per clean-up. The QuEChERS method allows you to use less hazardous solvent in much reduced volumes. The costs of hazardous solvent disposal and general large volume solvent disposal are eliminated. At the same time, you will attain a much better cleanup of the samples, which will help increase analytical column lifetime, saving costs in buying new columns.
5. How do you select the appropriate dSPE kit for the QuEChERS method?
UNIVERSAL dSPE kits designed to work for a wide variety of matrix including apples, oranges, lettuce, coconuts, avocados, nuts, seeds, spinach, berries, peppers, chocolate, black olives, dirt, beef, fish, protein tissue, water, etc.
Since CarbonX dSPE kits do not have the same problems as kits containing GCB, so there is no need to have several part numbers for high, med, and low amounts of GCB. CarbonX dSPE also has been proven to remove more matrix than other leading brands. Thus, we recommend CarbonX UNIVERSAL dSPE kits for all matrices. The UNIVERSAL CarbonX dSPE kit contains MgSO4/PSA/CarbonX/C18E kit
6. I am not regulated by either the AOAC or EN standards. Which extraction kit should I choose?
If you are analyzing a large number of pesticides or the analytes of interest are pH dependent, you can use either buffered extraction kit. If you are only interested in several compounds or the target analytes are not pH dependent, the original non-buffered kit can be used.
7. What is the difference between the AOAC and EN QuEChERS method?
The AOAC and EN QuEChERS methods are both buffered and differ in the choice of buffering salts in the extraction step as well as the ratios or proportio
ns of sample to salts and dSPE sorbent in the dispersive cleanup step. Sorbents are different because GCB has been specified by leading manufacturers. However, CarbonX
UNIVERSAL dSPE kits.
The 1 mL dSPE kit is appropriate for laboratories using large volume injection for GC/MS. The 15 mL kit requires concentration of the final extract and solvent exchange to toluene for GC/MS in order to achieve 10 ng/g detection of the pesticides.
9. What is the role of magnesium sulfate in the extraction and dispersive cleanup step?
Magnesium sulfate is added to absorb water in both the extraction and cleanup steps. In the extraction step, it also increases the ionic strength of the aqueous
mixture and induces phase separation with acetonitrile.
10. My QuEChERS analysis includes quite a few acidic pesticides. Will PSA lower their recoveries? What modification can I adapt?
It is possible that PSA sorbent retains acidic analytes because of the positive charge on nitrogen at pH < 8. If this is a concern, we recommend you adjust the pH to protonate the acids. You can adjust the pH with TFA, do the dSPE, then remove the volatile acid under a nitrogen stream. You can also omit the dSPE step and dir
ectly analyze supernatant from the extraction step but you will likely experience liner and/or column fouling.
11. Why does the QuEChERS method recommend homogenizing frozen sample with dry ice/liquid nitrogen and extracting samples while frozen?
The tubes have been formulated for cryoextraction methodology. If you do not cryo homogenize, you will overextract your sample. QuEChERS is made to be a “just enough” technique. This means that “just enough” sorbent is added to get rid of the matrix and not the analyte. Homogenizing frozen s
12. When I reconstitute my extract obtained using the QuEChERS method in the LC/MS mobile phase solvent, precipitates appear. What can I do to overcome this? ample with dry ice or liquid nitrogen prepares the sample into a fine powder (smaller particle size & more evenly homogenized), maximizing surface area for extraction while making sample easier to handl
e. Samples should be extracted while frozen to prevent analyte degradation.
If precipitates appear during reconstitution, you can sonicate and centrifuge to see if precipitates go into solution. Change your reconstitution solvent to a stronger solvent or add some water. Sonicate and vortex before adding water.
13. Why is the original QuEChERS method non-buffered?
The original non-buffered QuEChERS method was developed for an analysis of fewer pesticides. When the method was used for a larger pesticide screen, quite
a few compounds demonstrated pH dependency. Therefore the buffered methods were introduced.
14. In the extraction step of the QuEChERS method, what are the AOAC guidelines for adding extraction salts, and solvent?
For every gram of homogenized sample, 1 mL of 1% acetic acid in acetonitrile and 0.5 g of anhydrous magnesium sulfate/sodium acetate (4/1, w/w) are
recommended per AOAC 2007.01.
15. In the dispersive SPE step of the QuEChERS method, what are the AOAC guidelines for adding magnesium sulfate and SPE sorbents?
For every 1 mL of sample from the extraction step, 200 mg in a 3:1 ratio of magnesium sulfate/SPE sorbent(s) is recommended. For example, when an
8 mL aliquot from the extraction step undergoes the dispersive SPE cleanup step, 1200 mg of magnesium sulfate and 400 mg of PSA is recommended.
16. In the QuEChERS method, how much (in volume) initial extract and dSPE extract should I expect after centrifugation?
A 15 g sample yields around 11-14 mL of initial acetonitrile extract, depending on the water content of the sample. In the dSPE step, almost half of the extract will be lost to dSPE blend of salts and sorbents, resulting in roughly 6 mL of final extract from a 15 g sample.
17. What modification can you apply for dry samples to improve the extraction step in the QuECh
For dry samples containing less than 80% water, you can start with half the sample amount and add cold water to make up water content to 15 g for the AOAC method and 10 g for the EN method. EN 15662 provides specific guidelines for water addition to different matrices. For example, addition of 10 mL of water is recommended for 5 g of cereal sample.
18. While using the QuEChERS extraction kit, I accidentally spilled some of the sal
ts when dispensing into the centrifuge tube. Will my results be affected?
Salts in the QuEChERS extraction step are used in excess. Primarily salts are added to remove some water and induce phase separation between acetonitrile
and water. Spilling some if it (<1g) will not affect your results.
19. Is it necessary to dry down and reconstitute the extract from the dSPE step in the QuEChERS method for LC/MS analysis?
Evaporating the sample and reconstitute it in initial LC mobile phase solvent improves chromatography. It is required if you are running reverse phase HPLC and your sample is in a nonpolar solvent such as toluene or hexane.
20. What is the approximate pH that samples will reach using citrate salts per EN 15662 method? What is the buffering range?
The pH range most samples will reach is between 5-5.5. The buffering range is approximately between pH 2-7.4