concentraion measurement - (Jun/11/2009 )

Hi,

I have a protein solution whcih is at a concentration of 50nmoles/gram ( as told by my senior). I am not sure what this means as it is nmoles/gram. Iam only used to working in nmoles/ml or ul , but I cnat understand what nm/gram mean? Can someone explain me this and also tell me what will be the fianl concentration ( in moles) of the same protein solution if Iam going to aliquot 30uL (Mw of protein= 10000). I need help from someone as my senior is not very kind.

Thanks
rax

rax on Jun 11 2009, 04:11 PM said:

Have you never used Xmoles per gram?

Ex 5 mol/gr simply means that you have 5 moles for each gram you take...
The n simply means nanomols...

and if you take 30µl it depends on how much gram you diluted in the 30µl..

ex calculation:


You have 10 nmol/ gram and you need a 30nmol/liter solution

then you need to take 3 grams and dilute this in 1 liter of water.
(if the 10nmoles refer to the 1 substance you need, I do not know what is in your product)

maybe you should give some more information, I do suppose your product is a powder, not a liquid? If it is a liquid you need to know the density of the liquid how many grams/ml)

Hi Pito,

Thanks for posting back. My substance is a liquid, and the details I metioned are the only details my senior gave and told me will be fine to finish the calculations. He also mentioned that the final answer will be 1.5nmoles ( ie in the aliquotted 30uL ). Iam still not convinced how I could come to this answer and Iam sure he is right.

could you explain this to me.

Thanks,
rax

pito on Jun 11 2009, 07:21 AM said:

rax on Jun 11 2009, 05:26 PM said:

I really cant see how to calculate this if you have no relation (density) given between mass and volume(liter)

If the solvent is water (which is often the case with proteins) you can mostly get away with the relation 1 g = 1 ml, thus you'd have 50 nmol/ml. But, it seems like a weird unit to provide a concentration in. Are you sure you're senior didn't simply misspeak?

Did you allready got an answer from your senior?

I do wonder how you should have done it, because its just not really possible.

just put your 30uL on a scale:

If your solution has x Mol / gram and after pipetting 30uL into another tube, that tube weights x gram, how many moles do you have now?

Hi guys, I've been reading every post on this topic, and the more I read it the more confused I get. It's defying all biochemistry laws, and definitely defies all my understanding of concentrations and molecular weight.

rax says the protein solution is at 50nmol/gram.
He/she also says the protein MW is 10,000.

Now, by definition MW = grams of a molecule (protein in this case) per mol. So, it is impossible to have 50nmol in 1 gram of protein, if its molecular weight is 10,000. So, either you have 0.1µmol in 1 gram of protein (0.1µmol/gram according to its MW), or the protein has a molecular weight of 20,000,000 (for it to possibly be 50nmol/gram).

Am I going crazy here, or just missing something?

I agree with SatanClaus and pito, it has to be a mistake, as it is just NOT possible.

You are missing that the SOLUTION of the protein weights 1 gram and this solution contains 50nM protein and the rest is presumeably water.

If 1g of a solution has 50nMoles, how many moles does 30uL of that solution have:

Accurate way:
Weight 30uL of that solution on a scale, calculate:

50 nMoles / 1g * (weight of 30uL in grams) = nMoles of 30uL solution

Approximation:
Water has a density of 1 kg/L, 50nMoles protein is a negligible weight (1 Mole = 10,000g -> 50n Moles = 500µg)

Therefore 50nMoles in 1mL: 50nMol / 1000µL * 30µL = nMoles of 30uL solution

Please note that the result is NOT a concentration - the original poster confused Molarity with Moles i suppose. The concentration is of course the same as before aliquoting.

warsel on Jun 18 2009, 12:59 PM said:

Thanks warsel... now it makes sense