Promega's LightSmith & Alk. Phos Activity (0/1)

[rayj at cts.com]

I recently tried Promega's LightSmith I Kit.  I labeled 2 oligos, one was a 21mer, the other a 30mer.  
After conjugating the oligos to the Alk. Phos., I found that the probes had greatly different activities.  
Something like 0.05 units/ul (for the 21mer) vs. 0.0003 units/ul (for the 30mer).  Since the alk. phos . 
was from the same lot number, I am must assume that this difference is the result of DNA on the surface 
of the Alk. Phos..  Has anyone else observed this phenomenom?  Or does any one know of any good 
references which discuss Alk. Phos. and conjugation of nucleotides or peptides (IgG) and the effects 
on activity.  

Any help or comments will be most appreciated.