making lb + amp broth - question (Dec/11/2008 )

I want to make a 10ml stock of LB + Amp (100ug/ml) broth to culture a colony that was grown on a LB + Amp plate overnight for a plasmid miniprep. I have LB media. The Ampicillin is sold in powder form with molecular weight of about 371. how do I make my broth from this?

add 1 mg ampicillin to 10ml of lb broth.

The usual approach is to make a stock solution of ampicillin at 100 mg/ml. Make it in 50% ethanol, and store it at -20, where it will not freeze. Add 1 ul of this stock per 1 ml of autoclaved LB broth or agar (after both have cooled below 55C).

thank you both!