Church's Buffer for Northern and Southern Blot Hybridization
1% BSA, 1 mM EDTA, 0.5 M sodium phosphate (pH 7.2), 7% SDS.
Filter sterilize.
Note: You need to use both monobasic and dibasic sodium phosphate together to make a 0.5 M solution adjusted to pH 7.2.
Reference: PNAS 81:1991-1995, April 1984.
Good luck with your experiments!