Sodium Sulfate Precipitation Problem

[WS]

Dear Colleagues,

I am about to precipitate some purified IgG by dialysis against 18% m/
v sodium sulfate (as I want to label the protein with an amino
reactive reagent, I cannot use ammonium sulfate, it's a convenient
quencher). I get a huge amount of precipitate after incubating at room
temp over night. However, the precipitate is floating on top of the
solution, especially after centrifugation (2000g for 20 min at 25
degC).
Any idea how I could obtain an ordinary pellet where one would expect
it?

Many thanks and best regards,

Wolfgang