If the target compound is a neutral compound and a hydrophobic non-polar filler (such as C4, C8, C18, etc.) is selected, it can be washed with water or a buffer used for cartridge equilibration. If the analyte has a strong adsorption force on the solid phase extraction column, a water-soluble organic solvent may be added to the washing solution to enhance the washing effect.
If the recovery is found to be reduced, collect this component and check if the target compound is eluted at this step. If the ionizable target compound has been neutralized by adjusting the pH and adsorbed by the hydrophobic force by the SPE cartridge, care must be taken to maintain the same pH during washing to avoid the target compound in the washing step due to pH changes. loss.
If the target compound is an anion or a cation (as extracted using an ion exchange cartridge such as SAX, PSA, NH2, SCX, CBA, and PRS), it can be washed with a buffer used for cartridge equilibration. For singly charged analytes, the ionic strength of the buffer solution should not exceed 50 mmol/L. For doubly charged analytes, the ionic strength of the buffer solution should not exceed 10 mmol/L.
Under certain circumstances, the presence of moisture can have an effect on the elution of the target compound and subsequent analysis. Therefore, the SPE cartridge must be dried before eluting the target compound.
The method of drying mostly uses positive pressure or negative pressure. The positive pressure is generally blown by the air or nitrogen at a certain pressure from the upper part of the SPE cartridge; the negative pressure in a vacuum given below the extraction column so that the residual moisture is removed from the SPE cartridge.
Sometimes, in order to better remove residual moisture, a small amount of polar organic solvent such as 50 μL of methanol can be used. If the target compound is more volatile, care should be taken to control the time during which the positive/negative pressure is removed to prevent the target compound from being lost during the drying process.
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