How to make a stock solution and then dilute to desired concentration?

Hey,

I'm doing an experiment on different anticoagulants by comparing how they effect different specific clotting factors (measured via a factor activity assay).

I have 2.5 mg of apixaban (in tablet form) and I wanted to make a stock solution out of it and then use 5 different final concentrations ranging from say 0 - 800 ng/ml i.e. 50ng/ml ... 150 ng/ml etc and use these solutions to spike normal plasma samples. Then I will perform the activity assays.

I'm stuck at how to make a) a stock solution of 2.5mg tablet and then B) make up the final concentrations i need

Any help is appreciated

Well in the context of Chemistry a stock solution is simply a solution with a known concentration that's usually at a Integer value e.g 10 mol dm3 HCl but doesn't have to be. It's a solution that is designed to be diluted.


2.5 mg is a tiny amount to work with. However your eventual concentrations are extremely dilute, so we'll try 100ml

So that would make a solution of concentration 0.025 mg/ml.

Your units are nanograms, so that's

25,000 ng/ml

The dilution equation to use is as follows:

CiVi = CfVf

Ci = Initial concentration
Vi = Initial volume

Cf = Final Concentration
VF= Final volume

From there we can work out the required volumes:

Ci will be 25,000 ng/ml
Vi will be how much you take of this. E.g 10ml
VF is the required (final volume)
Cf is final concentration

So to dilute the stock solution to make a solution of e.g 50ng/ml. You would need a volume of water (or solvent) of:

25,000*10/50 = 5000ml

So it's clear that the stock solution needs to be far more dilute, you don't want to use 5L of water for an experimental dilution!

So adjusting the stock solution to make it about 250ng/ml. It works out that you would require 10L of water with a 2.5mg of tablet to make 250ng/ml.

(Take 2,500,000ng/250ng/ml).

This stock concentration would make the solution easier to dilute.

Taking Ci as 250 ng/ml and Vi as 1ml (taking 1ml of this)

Target 50ng/ml

250/50 = 5ml

Meaning you only require 5ml of solvent to dilute this volume (1ml) stock solution to make a 6ml solution of 50ng/ml. Far better.

So use CiVi = CfVf and don't be afraid to play about with the numbers. Just be careful with units.

(I'm a pure Chemistry Student so I'm not used to nanograms lol).