Chromatography Forum

Hello, I am preparing organic solutions containing methanol as a solvent with components benzene, toluene and xylene at ppm level (mg/L). I am using glass volumetric flasks with glass stoppers of 100mL, 50mL and 25mL capacities. I prepare a stock solution then dilute it down to the concentration I require.
I have been preparing and keeping the solutions in the lab which is controlled at 20-22C. I make sure that the flasks are stoppered tightly each time after I use them.

Will there be significant changes in the concentration of the solutions I prepared from the day I prepared it to the next few days until the solution is utilized? Depending on my usage, it could take me a few days or in some case one week until I use up the solution and I will have to make more solutions.

Thank you for your help.

I would use multiple vessels of a smaller size to store your stock solutions and then use one to prepare your dilutions each day.

For example if you had 10mL volumetrics then I would make 100mL of the stock solution and put 10mL into each 10mL vessel and use one at a time to make dilutions as needed daily.

Then you don't have to worry about loss of aromatics in the headspace of the larger vessel as it is emptied.

best wishes,

Rod

Assuming your system is stable over a week, you should not have significant changes for BTEX from the same vol. fl. Check the RSD of the procedure. Keep your solutions away from light and tightly closed. Do not use solution if it is less than 1/3 of the flask.
If you see big changes then it is more likely from what you do next, e.g. different pipettes or touch syringe glass barrel with fingers that may cause expansion. Consider Hamilton 1800 series.

Assuming your system is stable over a week, you should not have significant changes for BTEX from the same vol. fl. Check the RSD of the procedure. Keep your solutions away from light and tightly closed. Do not use solution if it is less than 1/3 of the flask.
If you see big changes then it is more likely from what you do next, e.g. different pipettes or touch syringe glass barrel with fingers that may cause expansion. Consider Hamilton 1800 series.

Thank you for your reply.
Unfortunately I don't have a set procedure which I am following. My experiment is not documented, I am mostly using ideas from journals which have done similar experiment to what I want to do. But I couldn't find anything that meets my plan exactly and I can't follow the experimental procedures mentioned in the articles due to the lack of equipment in the lab I use.

I would use multiple vessels of a smaller size to store your stock solutions and then use one to prepare your dilutions each day.

For example if you had 10mL volumetrics then I would make 100mL of the stock solution and put 10mL into each 10mL vessel and use one at a time to make dilutions as needed daily.

Then you don't have to worry about loss of aromatics in the headspace of the larger vessel as it is emptied.

best wishes,

Rod

Thank you Rod for your suggestions. It is a very good idea.