Are Buffer PB of the QIAquick PCR Purification Kit and Buffer QG of the QIAquick Gel Extraction Kit interchangeable?

Buffer PB of the QIAquick PCR Purification Kit cannot be used to extract DNA from agarose gels. However, Buffer QG of the QIAquick Gel Extraction Kit can be used to remove salt and proteins from enzymatic reactions by adding 3 volumes of Buffer QG and 1 volume of isopropanol to the reaction and proceeding with step 6 of the Gel Extraction Spin Protocol in the QIAquick Spin Handbook. See the QIAquick Spin Handbook for a list of reactions which can be cleaned up with the various QIAquick kits.