How do you desalt sea water samples?

Depending on the analytes of interest, you can use various SPE sorbent chemistries to selectively retain your analytes, while salts pass through the cartridge unretained during sample loading.  An example of this is if your analytes have retention in the Strata X sorbent, a reversed phase method can be used to capture analytes, the sample can then be washed to further remove interferences and finally a methanol elution can recover analytes.  This method can desalt the sample and provide a cleaner, more concentrated extract at the same time.