cDNA precipitation without coprecipitation of primers

[Simone Marker]

Hi,

I need to remove a 47bp primer from an RT reaction, i.e. I want to 
precipitate the synthesised cDNA without the coprecipitation of the primer. 
The easiest way would be the purification by spin coulmn, but the amount of 
my cDNA is very low, so that I'm afraid to lose the cDNA on the column. Does 
anyone know about precipitation conditions (isoprop/ethanol,different salts) 
that eclude the coprecipitation of smaller nucleic acid fragments? (my cDNA 
is at least one kb)

and in general: does anyone know if cDNA requires different precipitation 
conditions than genomic DNA or RNA?