Chromatography Forum

I need to prepare a 10,000 ppm solution of 3-Pentanol. The final volume needs to be 500 mL.

The 3-Pentanol I have is 98% pure

I need to prepare a 10,000 ppm solution of 3-Pentanol. The final volume needs to be 500 mL.

The 3-Pentanol I have is 98% pure

I need to prepare a 10,000 ppm solution of 3-Pentanol. The final volume needs to be 500 mL.

The 3-Pentanol I have is 98% pure

If me, I'd weigh 10.2 g 3-pentanol into a 100ml volumetric flask (10.2 g accounts for 98% purity of the 3-pentanol), that's 10% w/v. After mixing and diluting to volume with your solvent, I'd pipet 50.00ml into a 500ml volumetric flask, and mix and dilute to volume with your solvent. This would be 1% w/v or 10,000ppm.

Thanks, but why do you recommend I abandon the density of the 3-Pentanol in the calculation?

Thanks, but why do you recommend I abandon the density of the 3-Pentanol in the calculation?

You don't need the density because you'd be WEIGHING the 3-pentanol, not adding it by volume.

Most results are reported in weight percent or weight ppm. Exception would be something like ethanol in beer/wine/spirits and hand sanitizers, or something like rubbing alcohol (2-propanol).

I want to add by volume.

I want to add by volume.

If you want your final dilution to be 10,000 ppm w/v:
Then add 12.5ml of your 3-pentanol into a 100ml volumetric flask (which can already contain some ethanol), that's 10% w/v. After mixing and diluting to volume with your solvent, I'd pipet 50.00ml into a 500ml volumetric flask, and mix and dilute to volume with your solvent. This would be 1% w/v or 10,000ppm w/v.


If you want your final dilution to be 10,000 ppm v/v:
Then add 10.2ml of your 3-pentanol into a 100ml volumetric flask (which can already contain some ethanol), that's 10% v/v. After mixing and diluting to volume with your solvent, I'd pipet 50.00ml into a 500ml volumetric flask, and mix and dilute to volume with your solvent. This would be 1% v/v or 10,000ppm v/v.

I want to add by volume.

If you want your final dilution to be 10,000 ppm w/v:
Then add 12.5ml of your 3-pentanol into a 100ml volumetric flask (which can already contain some ethanol), that's 10% w/v. After mixing and diluting to volume with your solvent, I'd pipet 50.00ml into a 500ml volumetric flask, and mix and dilute to volume with your solvent. This would be 1% w/v or 10,000ppm w/v.


If you want your final dilution to be 10,000 ppm v/v:
Then add 10.2ml of your 3-pentanol into a 100ml volumetric flask (which can already contain some ethanol), that's 10% v/v. After mixing and diluting to volume with your solvent, I'd pipet 50.00ml into a 500ml volumetric flask, and mix and dilute to volume with your solvent. This would be 1% v/v or 10,000ppm v/v.

But then think again, why is the error of pipettes determined by weighing?

If you weigh, then the density is not used because it connects the volume and mass. So check the units as described in the other thread (https://www.chromforum.org/viewtopic.php?t=122227)

Also the density, the volume of the liquid, is temperature dependent, while the mass is not.
Further, except if using a burette, you often don't have a volumetric pipette of the exact volume needed e.g. I've never seen a volumetric pipette of 10.2 or 5.1 ml. Do you have such one?

The point of solvent evaporation during weighing is a valid one but countermeasures can be taken (and once the flask is closed, you can note the exact mass of reagent added. something you don't know with volumetric method; you don't know how much did evaporate...)

But best if you make your own experiments: take an inexpensive solvent like ethanol or isopropanol and dispense a certain volume of your choice in a tared and closeable container and weigh back. Do it 6+ times to see how repeatable and accurate it is. Also test the same thing by direct weighing, then compare your results.

Also with your standard, I guess in the end it will be quantified against the preceeding batch of the standard. So you will see the result of your work. If allowed, prepare two batches, one with each method and compare.

I see what you are saying. Correct me if I'm wrong: you are suggesting that the lack of available volumetric pipettes, coupled with the theoretical fluctuation in ambient temperatures, make using density and adding a reagent solution by volume inaccurate. And I also think you are saying that weighing the liquid, ignoring the density in the calculation, and only using the purity, and furthermore taking precautions to reduce evaporation during transfer, is the best way to make a standard solution from a reagent solution (such as 3-Pentanol).
I had been using a calibrated pipettor for my standard prep. I have over 20 volatile liquid compounds in my mixed standard. My reasoning there is twofold: I could make the transfers faster than weighing (reducing evaporative loss), and thus make my mixed standards much faster than weighing. Also, when weighing multiple standards into the same flask, there is a much greater chance over overshooting the weight.