Solid phase extraction is a pre-treatment method for separating the selective adsorption capacity of different components in the sample by a solid adsorbent. Solid phase extraction technology is the most commonly used technical means in food testing, and below lists problems and solutions in solid phase extraction.

1

Problem: The recovery rate of the target compound is low (the target compound is not or partially adsorbed on the SPE column)

Reason 1: SPE column is not well pretreated
Solution: Reverse column: treat the column with methanol, isopropanol or ethanol, and then treat the column with the solvent of diluting the sample. Be careful not to dry the SPE column.

Reason 2: Improper polarity of SPE column
Solution: Select the SPE column with obvious selectivity for the target compound.

Reason 3: The affinity of the target compound to the sample solution is much greater than that to the SPE column
Solution: change the polarity or pH of the sample solution to reduce the affinity of the target compound in the sample solution.

Reason 4: When a large volume of water sample passes through the SPE column, the reversed-phase column packing loses the methanol left by the column pretreatment
Solution: Add 1% – 2% methanol or isopropanol or acetonitrile to the sample solution.

2

Problem: The recovery rate of the target compound is low (the target compound is not washed out of the SPE column)

Reason 1: Improper polarity of SPE column
Solution: Select other SPE columns with low polarity or weak selectivity.

Reason 2: The elution solvent is not strong enough to elute the target compound from the SPE column
Solution: Change the pH of the elution solvent to increase its affinity for the target compound.

Reason 3: The volume of elution solvent is too small
Solution: Increase the solvent volume.

Reason 4: The target compound is irreversibly adsorbed on the SPE carrier
Solution: Reverse phase: select the carrier with weak hydrophobicity. If the original C18 is used, it is changed to C8, C2, CN.
Cation exchange: replace benzene sulfonic acid with carboxylic acid.
Anion exchange: replace tertiary amine with primary amine and secondary amine.

3

Problem: Poor reproducibility of extraction

Cause 1: The SPE column was dried before the sample was added
Solution: Re-process SPE.

Reason 2: The SPE column capacity exceeds the threshold
Solution: reduce sample quantity or choose large capacity column.

Reason 3: The sample flow rate through the column is too fast
Solution: Lower the flow rate.

Reason 4: The eluent flow rate was too fast
Solution: Permeate the column with eluent before applying external force. Two 5ml elutions may be more effective than one 10ml elution.

Reason 5: The solubility of the target compound in the sample was too large, so the sample passed through the column at the same time as the sample and was not retained
Solution: Change the solubility of the target compound by changing the sample polarity or pH.

Reason 6: SPE columns are treated with polar solvents and the eluents are incompatible with non-polar solvents
Solution: Dry the SPE column before using a non-polar solvent.

Reason 7: The solvent used to wash the impurities was too strong, and some of the target compounds and impurities were eluted from the SPE column at the same time. How much of the target compound is lost at this stage depends on the flow rate of the detergent, the characteristics of the SPE, and the volume of the detergent.
Solution: reduce the strength of the washing solvent.

Reason 8: Eluting fluid volume is too small
Solution: Increase the volume of eluent.

4

Problem: In an inverted SPE column, the eluting fraction contains water

Reason: The SPE column was not properly dried prior to elution of the target compound
Solution: Dry SPE column with nitrogen or air: remove residual moisture from SPE column with 20-100 μL containing 60%-90% methanol-water.

5

Problem: The elution fraction contains interferents


Reason 1: The interfering substance and the target compound are eluted at the same time
Solution 1: Wash the interferents out of the SPE column with medium polarity solvent before eluting the target compound. Two or more solvents can be mixed to achieve different polarities.
Solution 2: Select SPE column with higher affinity for target compounds and low affinity for interferents.

Reason 2: The interferents come from the SPE column
Solution 1: Use two SPE columns with different polarity to remove interferents. Such as reversed-phase column and ion exchange column or silica gel column.
Solution 2: Wash the SPE column with eluting solvent before column pretreatment.

6

Problem: SPE column flow rate decreased or blocked


Reason 1: There are too many particles in the sample
Solution: Filter or centrifuge the sample.

Reason 2: The sample solution viscosity is too high
Solution: Dilute the sample with solvent.

7

Problem: Extraction of nonpolar target compounds from solid samples by reversed-phase column


Reason: The target compound is not in liquid solution
Solution: Homogenize the sample with methanol, isopropanol or ethanol. Then centrifugal filtration, and then dilute the clear liquid with water to an aqueous solution with a water content of 70% – 90%.

8

Problem: The target compound was extracted from solid samples by normal phase column

Reason: The target compound is not in liquid solution
Solution: Use non-polar solvent (such as n-hexane, petroleum ether, chloroform, etc.) slurry.

If you have any problem or require further information, please contact info@welchmat

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