Dilution Equation With Low Concentration Diluent - (Jun/09/2015 )
I am currently working on a dilution and need some help. Normally I use the C1V1=C2V2 equation when the diluent is DI water or something with no concentration.
However, I am working with trying to dilute down a sample with a concentration of say, 900ng/mL. The diluent I am using has a concentration of 20ng/mL. Is there an equation that I could use to do a 1:5 dilution of the sample using the diluent? I don't think I can use the C1V1=C2V2 because of the 20ng/mL diluent would throw off the end result and it wouldn't be a true 1:5 dilution.
Any help is appreciated.
It's simple really, you would need to solve with two equations.
(C0V0 + C1V1) = C2V2
C0 = 900 ng/ml
C1= 20 ng/ml
C2 = desired concentration
V2 = desired volume
Your variables are V0 and V1.
So you have:
V1 = V2 - V0
C0V0 +C1(V2-V0) = C2V2
C0V0 + C1V2 - C1V0 = C2V2
(C0-C1)V0 = C2V2-C1V2
...Which eventually results in:
V0 = (C2-C1)V2 / (C0-C1)
V1 = V2 - V0
You want 5 ml of a 100 ng/ul solution.
V0 = (100-20)*5 / (900-20)
V0 = 0.454 ml
V1 = 4.545 ml
0.454 ml * 900 ng/ml = 408.6 ng
4.545 ml * 20 ng/ml = 90.9 ng
Total = 408.6 + 90.9 = 499,5 ng
499,5 ng / 5 ml = 99,9 ng/ml ~= 100 ng/ml (0.1 lost to approximation).