Question

You have 0.5 ml of a stock solution of 1 mg/ml BSA. You need at least 200 ul of the solutions listed below. Calculate the volume of BSA needed and the volume of water needed to make the solutions.
25 ug/ml
50 ug/ml
75 ug/ml
100 ug/ml
150 ug/ml
200 ug/ml

Answer 1

Dear Student,

we know

1liter = 1000ml ,1ml = 1000 µl

1 gram = 1000mg , 1 mg = 1000 µg

There are 0.5 ml of a stock solution of 1 mg/ml BSA.

0.5ml=0.5*1000ul=500ul

1mg/ml=1000ug/ml

Therefore There are 500ul ml of a stock solution of 1000ug/ml BSA.

we  use the formula:

V1C1=V2C2 where V1 = volume of BSA needed and C1 = concentration of stock solution

v2= volume of stock solution, C2= conc. of the final stock solution

therefore, for 25 ug/ml

V1= (500ul*25 ug/ml)/1000ug/ml)

v1=12.5ul (volume of BSA needed)+ 187.5 ml (volume of water to make up the the volume 200ml)

for 50 ug/ml,

v1=25ml+175ml water

for 75 ug/ml,

v1=37.5ml+162.5ml water

for 100 ug/ml

v1=50ml+150ml water

for 150 ug/ml,

v1=75ml + 135ml water

for 200 ug/ml

v1=100ml+ 100ml water

example

Given a stock of 100 mg/ml BSA, prepare 1 ml of 0.02 mg/ml BSA solution.

C1 (stock solution) = 100 mg/ml

C2 (final solution) = 0.02 mg/ml

V2 (final volume) = 1 ml V1 (stock solution) = ?

V1 = (0.02mg / ml)(1ml)/ (100mg / ml)

V1 = 0.0002ml

This is a very small quantity; we cannot pipet 0.0002 ml (0.2 ul) accurately. We have to do a stepwise dilution. First, dilute the stock solution 100-fold to make a 1 mg/ml solution. How can we do this? First, let’s make 10 ml of the 1/100 dilution:

C1 V1 = C2V2

(100mg / ml)V1 = (1mg / ml)(10ml)

V1 = (1mg / ml)(10ml) /(100mg / ml)

V1 = 0.1ml

So, we place 0.1 ml of the 100 mg/ml stock solution of BSA into a container and add (10 mL-0.1 ml = 9.9 ml) of solvent to get 10 ml of 1 mg/ml solution of BSA. Now to prepare the solution we wanted in the first place we use the 1/100 dilution as our new “stock” solution:

C1 V1 = C2V2

(1mg / ml)V1 = (0.02mg / ml)(1ml)

V1 = (0.02mg / ml)(1ml)/ (1mg / ml)

V1 = 0.02ml

Regards