Micromolar (and molar) is a concentration and is independent of volume. So you would never have 100 micromolar per 10 ml, but you might have 10 ml of a 100 micromolar solution. However you could have XXX micromoles (which is an amount) per some volume, so 100 micromoles of some compound in a liter would be 100 micromolar.

Michael J. Benedik Thank you sir. So, you mean to say even if withdraw 100 microliter from 10ml (containing 50micromolar) it will have 50 micromolar both in the 100microliter as well as in remaining 900microliter? Please clarify this.

Thank you.

Micromolar is a concentration. No matter how much you remove, if you start with 50micromolar, it will always be 50 micromolar solution. However if you take your 100microliter (containing a 50micromolar solution) and then add it to water or buffer, you will now dilute and change it. So taking 100ul of a 50uM (micromolar) solution and putting into 900ul of water will now give you 1ml of a 5uM solution.

Michael J. Benedik Ok sir. I got to know if we dilute that 100microliter with 900 microliter of water the concentration will get reduced. But, my doubt is that the remaining 900microliter from where i took (In this case we can keep it as stock solution) the 100microliter will also contain 50micromolar ?

You are confusing concentration and amount. Micromolar is like mg/ml, a concentration. So if you have a solution that is 20mg/ml, then it doesn't matter if you have 1 liter or 1ml, the concentration is always 20mg/ml. However the actual amount of the substance is different because you have different volumes. So in 1 liter you would have 20gr of the substance and in 1ml you would have 20mg of the substance, but the concentration is the same.

So with micromolar it is the same. The concentration does not change with volume, but the actual amount of micromoles of the substance will be different in the different volumes. Micromolar is a concentration, micromoles is an amount.

Michael J. Benedik Thank you so much sir. I got it. So the micromolar is basically a concentration, which will remain same until and unless it is diluted. Is that correct sir?

Actually, I facing issue with the below problem. Can you please help in solving it:

1. Initially I have dissolved 20mg of the sample (drug A) in 1ml of solvent. This leads to 70.3359 mm of the solution (Calculated based on the molecular weight of drug A).

2. Further, 100 microliters of the above solution was taken and diluted with 1350microliters of water. This gives a molarity of 5.22 mm.

3. Later, 100microliters from the above solution was taken and diluted upto 10ml of solvent. This gives a molarity of 52.2 micromolar.

4. So from the above solution (obtained in 3rd step), I'm taking 200microliter without any dilution. So now this means that 200microliters is also having 52.2 micromolar. Is that right sir? Kindly correct me if I'm wrong.

Thank you.

Assuming your initial calculation of the molarity is correct (is the MW about 285?) then yes your 200microliters would still be 52 micromolar (uM)

Yes sir molecular weight of my drug A is around 284. Thank you so much for the clarification.