Dilution calculations in research?

[lemonade123]

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I've been working in a research lab for about 2 months now, and the post-doc I work with, when teaching me new research methods, is always asking me to do dilution calculations on the spot. For example, she'll say, "Okay if this plasmid's concentration is 1000 ng/microliter, how much would you take out to dilute it 10x? Dilution calculations have always been confusing to me, and it's been hard for me to do them on the spot like that! Do you basically just use m1v1=m2v2? I havent taken the chemistry labs yet, which I assume would help.

Today in lab after measuring a DNA sample concentration to be 278 ng/microliter, she told me to take 1 microliter from the sample, then add in 27 microliters of water. What exactly did she do there (or how much did she dilute it by)? I ask her to explain these to me but she always just gives me the answer, never how she got the answer.

Can someone simplify general dilution calculations for me?

 

[Baller MD]

First question: 1 microliter plasmid mix + 9 microliter water = 10x dilution.

Via Android

 

[blomar]

if you want to dilute it 10x, you take 10% of the volume of the original and replace the other 90% with whatever you're diluting it with (eg water). say you have 10ml of 1M solution and you want 10mL of 0.1M solution, you just take 1mL of the 1M and add 9mL of water.

278 ng/microliter * 1 microliter(concentrated sample)/28 microliters(total volume) gives you a 278ng/28 microliter so it's diluted to a 10ng/microliter solution.

Stoichiometry is definitely something you need to learn if you haven't yet...it's really basic math once you figure it out

 

[seracus]

So if you want to dilute a solution, you want to add more solvent (the solvent depends on the solution and could be water, acetone, etc.). Usually you do not want to dilute the entire batch of concentrated solute, so you first have to decide what volume of the diluted solute you want for your experiment.

Let's say you need 1 ml of diluted solution for a particular experiment. The concentrated solute is in a water solvent at 5 micrograms/ml. Your experiment requires the concentration to be 1 microgram/ml, so you need to add more water.

(5 ug/ml)*(x ml) + (0 ug/ml)*(1-x ml) = (1 ug/ml) * 1 ml

Where 5 ug/ml is the concentration of the concentrated solution, 0 ug/ml represents water, 1 ug/ml is the target concentration, 1 ml is the final volume needed, x is how much of the conc. solution you need, and 1-x is how much solvent you need.

Some quick algebra...

5*x = 1, x = .2

So you would need 0.2 ml of conc. solution and 0.8 ml of water.

General formula:

c(initial) * v(solution) + c(solvent: always 0)*(v(final) - v(solution)) = c(final) * v(final)

Where c stands for concentration and v for volume. Make sure that c(i) and c(f) are in the same units. This equation usually simplifies to the following:

c(i) * v(solution) = c(f) * v(f)

and for solvent, v(f) - v(solution) = how much solvent you want to add