Preparation of stock solutions.
filter sterilization; or preparation from the sterile water and the sterile powder;
store at -20
C in small quantities (about 10 freezing-thawing cycles);
instead of H
O it is possible to use 50% glycerol. The advantage - solution is liquid at -20
some laboratories use 96% (or 50%) EtOH for ampicillin solubilization. There are two advantages in this method: (i) solution is liquid at -20
C, (ii) the solution is self sterilizing. But the disadvantage it very serious: ethanol is a weak catalyst of b-lactam ring disruption. So, solution is unstable.