Hello Ahmed Al-Omar

You can use the formula N1x V1 = N2 x V2

where N1= Strength of Penstrep (stock) = 100X

V1 = Volume of 100X Penstrep to be added (a)

N2= Strength of Penstrep in the culture medium= 1X ( same as 1%)

V2= Volume of culture medium (500ml + 56 ml =556ml)

Therefore,

100X x a = 1X x 556ml

Thus, a = 556 x 1X / 100X = 5.56ml

So, you need to add 5.56ml of 100X Penstrep to 550.44 ml of RPMI medium containing FBS so that the total volume of the RPMI + FBS + 1% Penstrep is 556.

After adding 56 ml FBS to 500ml RPMI, you need to remove 5.56ml of culture medium and add 5.56 ml of 100X Penstrep so that the total volume of culture medium remains constant at 556ml.

This will give you 556 ml medium (500 RPMI + 56 FBS) with 1% antibiotic.

Best.

Hi Ahmed Al-Omar

494.44 mL RPMI+5.56 mL 100% pens-strep+56 mL FBS= 556 mL RPMI with 1% pens-strep.

You can take out 5.56 mL RPMI from your original 500 mL stock and add there 5.56 mL 100% Pens-Strep, then add there 56 mL FBS. Mix well.

Hope it helps.