purification of radioactive probe

[Simone Marker]

Hi,

does anyone know if it is really necessary to purify a radioactive DNA probe 
after labelling it by random priming? I want to use it on a northern blot. 
So far, I worked with DIG-labelled probes, that do not need to be purified 
after labelling. They are used directly in the hybridisation solution. Is it 
different with radioactive probes? Do you think that precipitation by salt 
and alcohol is sufficient for purification?

Thank you very much,
Simone