What distinguishes the QuEChERS extraction method from Salting-Out Liquid-Liquid Extraction (SALLE)? Is it the drying agent (MgSO4) or the buffers added during the extraction step?
The "drying agent (MgSO4)" and "the buffers added in the extraction step" are improvements of the protocol for the SALLE. In other words, QuEChERS is the result of the changes that have improved the SALLES protocol.