A simple pretreatment is to add 10% TCA (trichloroacetic acid) aqueous solution in the ratio of 1:1.  Centrifuge and collect the supernatant. 
 
Another simple way to pretreat whole blood is to perform protein precipitation with cold acetonitrile-methanol (85:15) in the ratio of 1:2.  After centrifuging, the supernatant is diluted with solvent appropriate for extraction loading.

A more thorough pretreatment is converting whole blood into blood plasma.  Centrifuging anti-coagulated blood gives blood plasma as supernatant.  Blood plasma preparation kits with prepackaged tubes containing an anticoagulant are commercially available.

For more information on sample pretreatment for extraction using Strata and Strata-X, please contact us.