Ampicillin stock solution

How to prepare Protocol for ampicillin 200 mg/ml stock solution stock (x 1000).

• Weigh 2 g ampicillin sodium sulfate powder (Fisher 1760-25) in a Falcon 15 mL tube.
• Add water to the 10 mL mark and vortex. Add more water if necessary.
• Filter through 0.22 uM membrane with a large syringe.
• store at -20 in 1 ml aliquots.

final concentration for E. coli should be 200 µg/ml. This is 2-10 times the recommended by ATCC (see below), but the higher concentration avoid satellite colonies.