# UA Biophysics:Protocols:Ampicillin

Ampicillin sodium salt

Ampicillin is a ß-lactam antibiotic that inhibits bacterial cell-wall synthesis by inactivating transpeptidases on the inner surface of the bacterial cell membrane. Ampicillin in solution is a function of pH, temperature and the identity of the buffer. It’s activity is quickly lost when stored above pH 7.

## STOCK SOLUTION

Ampicillin is usually used at a concentration of 50 - 100 µg/mL. Stock solution is typically at 25mg/mL

## PROTOCOL (STORAGE)

1. According to desired amount of antibiotics, calculate the amount in grams that has to be weighed.
1. For example, for 10mL of 25mg/mL of Ampicillin:

25mg/mL*10mL=250mg

1. Ampicillin is soluble in ddH2O.
2. Filter sterilize solution using a 0.2 µm syringe filter.
3. Divide in aliquots of 500μL
4. Store at -20 °C. up to 4-6 months

"It is stable at 37°C for three days. Additional studies have shown that the stability of Ampicillin in solution is a function of pH, temperature and the identity of the buffer. It′s activity is quickly lost when stored above pH 7. " Sigma

## USAGE

For culture plates, allow media to cool to 55 °C before adding ampicillin to a final concentration of 35-50 μg/ml.

For Example, for 300 mL of media at a final concentration of 50µg/mL:

Ci Vi = Cf Vf

25mg/mL* Vi = 0,05mg/mL*300mL

Vi = 15mg/(25mg/mL)

Vi = 0,6 mL