How do you perform a wash study for solid phase extraction?

You can perform a wash study by setting up a series of extractions with different wash strengths.  

It is best to keep all other parameters the same during the study.  Washes with 5 to 10% increments of the modifier (i.e. methanol in RP methods) are applied from 0% going up to 80% depending on the properties of analytes being extracted.  

For hydrophobic analytes, you can go up to 80%.  For more water-soluble analytes, go up to 40%.  The breakthrough data will help optimize the % modifier for a balance between cleanup without compromising recovery.