How to Improve Unsatisfactory Purification Effect of Solid Phase Extraction?

If you are experiencing an unsatisfactory purification effect in Solid Phase Extraction (SPE), there are several troubleshooting steps and optimization strategies you can consider. Here are some suggestions to improve the purification efficiency:

  1. Optimize Sample Loading:
    • Ensure that you are not overloading the SPE cartridge with too much sample. Overloading can lead to poor recoveries and reduced purification efficiency.
    • Adjust the sample volume based on the recommended loading capacity of the SPE cartridge.
  2. Optimize pH of Sample and Mobile Phase:
    • Check the pH of your sample and the mobile phase used during the extraction process. Some compounds may have better retention under specific pH conditions.
    • Adjust the pH of the sample or mobile phase if necessary.
  3. Select the Right SPE Sorbent:
    • Choose an SPE sorbent with properties suitable for your target compounds. Different sorbents have varying affinities for different types of analytes.
    • Consider the polarity, particle size, and specific interactions of the sorbent with your sample.
  4. Condition the SPE Cartridge Properly:
    • Ensure that you properly condition the SPE cartridge with the recommended solvents before loading the sample. This prepares the sorbent for optimal interactions with the sample.
  5. Optimize Elution Solvent:
    • Experiment with different elution solvents or solvent mixtures to find the most effective conditions for eluting your target compounds.
    • Consider using a gradient elution if necessary.
  6. Improve Washing Steps:
    • Enhance the washing steps to remove interfering compounds and contaminants effectively.
    • Adjust the composition and volume of the wash solvent to achieve better purification.
  7. Control Flow Rates:
    • Maintain consistent and controlled flow rates during sample loading, washing, and elution. Extreme flow rates can impact the efficiency of the SPE process.
  8. Prevent Sample Matrix Effects:
    • If the sample matrix is causing interference, consider additional sample cleanup steps or modifications to minimize matrix effects.
    • Optimize the SPE method for specific sample types.
  9. Evaluate Sample Matrix Compatibility:
    • Ensure that the sample matrix is compatible with the SPE sorbent. Incompatibility may lead to poor recoveries.
    • Consider sample pre-treatment or dilution if necessary.
  10. Use Proper Storage Conditions:
    • Store the SPE cartridges under recommended conditions to maintain sorbent integrity.
    • Check the shelf life of the SPE cartridges and replace them if expired.
  11. Check for Column Clogging:
    • Monitor the SPE column for signs of clogging, and replace the column if necessary.
    • Use proper filtration to prevent particulate matter from entering the column.
  12. Verify Extraction Solvent Compatibility:
    • Ensure that the extraction solvent used for the sample preparation is compatible with the SPE sorbent.
    • Check for potential interactions between the extraction solvent and the sorbent.
  13. Optimize Sample Matrix pH:
    • Adjust the pH of the sample matrix if necessary. pH can affect the extraction efficiency of certain compounds.
  14. Consult Application Notes and Literature:
    • Refer to application notes, literature, or guidelines provided by the SPE column manufacturer for specific recommendations and optimizations related to your target compounds.
  15. Perform Method Development:
    • Conduct systematic method development to optimize SPE conditions for your specific analytes and sample matrix.

If problems persist, consider consulting with technical support from the SPE column manufacturer or chromatography experts to address specific challenges associated with your purification process.

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In addition, solid phase extraction is a sample pretreatment method based on chromatographic separation, and it is a relatively mature sample pretreatment method that has been used in recent years. Today, HAWACH will discuss how to improve the unsatisfactory purification effect of solid phase extraction. It is recommended to consider the following points.

1. Improvement of purification mode
Generally speaking, the mode of retaining the target compound is better than the mode of retaining the impurities. If the item being analyzed is a certain type of compound analysis, it is better to use the purification mode of retaining the target compound. For example, for the same analysis of carbendazim and thiabendazole (a type of alkaline pesticide) in vegetables, the use of cation exchange columns can specifically retain these pesticides, so that they are completely separated from interferences, and using normal phase adsorbent or graphitized carbon black to retain interferences can only remove the main interferences, and there are still many interferences remaining.

In addition, if more than one SPE cartridge can be used for the purification of the target compound, an adsorbent with good selectivity should be selected in terms of selectivity: ion exchange > normal phase > reversed phase.

2. Optimization of leachate and eluent
For reversed-phase mode and normal-phase mode, the elution intensity of the leachate should be increased and the elution intensity of the eluent should be reduced without affecting the recovery rate.

For reversed-phase mode, the target compound can be loaded in an aqueous solution, and elute with 5%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, 100% methanol aqueous solution in sequence, collect the eluate and analyze separately, establish the elution curve, find out the solvent system when the target compound is eluted.

The content of methanol in the eluate should be slightly lower than the solvent system when the target compound is just eluted, and the methanol content in the eluent should be slightly higher than the solvent system when the target compound is completely eluted. When pure methanol cannot elute the target compound, the elution curve of the methanol-methyl tert-butyl ether mixed solution should be tested: For some ionic compounds that are neither soluble in water nor soluble in methanol, acid or base can be added to the solvent system.

For normal phase systems, load the target compound’s n-hexane solution, then use 5%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, 100% n-hexane methyl tert-butyl ether solution for elution in sequence, separately collect the eluate for analysis, establish an elution curve, and find out the solvent system when the target compound is eluted. The content of methyl tert-butyl ether in the leacheate should be slightly lower than the solvent system when the target compound is just eluted, and the content of methyl tert-butyl ether in the eluent should be slightly higher than the solvent system when the target compound is just completely eluted.

3. Properly treat the SPE cartridge
The adsorbent in the SPE cartridge may contain a small amount of interferences. Effective activation can prevent these interferences from entering the eluent. The activation solution should select a solvent system with strong elution strength throughout the operation; in reversed phase mode, it mainly involves 0%-100% methanol aqueous solution from sample solution to eluent, so the activation solution should be pure methanol. When the target compound needs to be eluted with a methanol-methyl tert-butyl ether mixture, the activation solution should be methyl tert-butyl ether.

In the normal phase mode, it mainly involves 0%-100% n-hexane-methyl tert-butyl ether solution from the sample solution to the eluent, so the activation solution should be pure methyl tert-butyl ether.