Incubate tubes on ice vs in the refrigerator - (Apr/17/2013 )

Maybe a dumb Q... but I've been doing a protocol for DNA isolation from soil that has a couple of precipitation steps that, after addition of solution and brief vortexing, says to incubate at 4 C for 5 min. I've just been sticking them in ice (a bucket of ice that itself is at RT). Can you see any problems in doing this?

Well, it will be at 0C rather than 4C, but that's probably better. Additionally, the ice bucket (especially if it is wet ice) will transfer heat much more quickly than putting a tube in the refrigerator.

Yeah, I did it to get the temp (inside the tubes) down faster since it only calls for 5 min. I didn't think it would be an issue (that somehow resulted in added contamination, particularly humic acids in this case), but there of couse always could be a mechanism that I'm not aware of that could occur if temp of solution got below 4 C.