Standart preparation

[ferish91]

Hello.i want analyze vodka by gc.i have satndart propanol 2. İts certified purity is 96percentage.how do i prepare stock solution?

[karbonat]

We work with the analysis of alcoholic beverages, in particular - with vodka too. Firstly it seems too me that 96% purity - is too low for correct quantification analysis. But if there is no choice, do it according to established practice. There is an ASTM standard D 4307-99 (there are newer ones, but this is one I have) where the procedure of Standard Solutions preparation is established.
Now about your problem. As vodka contains volatiles, particularly 2-propanol usually in very low concentrations (1-20 mg/L absolute alcohol, AA), you can prepare standard solution only by dillution. So I can advice you to prepare a standard solution with 2-propanol concentration of nearly 5000 mg/L AA, then dilute it to nearly 300-500 mg/L 2-propanol concentration. Finally dillute the last one to receive extremely low volatile concentrations (1-20 mg/L AA). That's how we do it. It's clear, that you should dilute and prepare samples in 40% water ethanol solution.
BUT! Be attentive, initial ethyl alcohol always contain volatiles, in particular - 2-propanol (we take the puriest ethyl alcohol and the concentration of 2-propanol in it is usually in range from 0,5 to 3 mg/L AA. So don't forget to take this into account and establish the content of pure ethyl alcohol which you are going to use as a matrix for your standard solutions.
If there are any other other questions, don't hesitate to ask me.

[ferish91]

[quote="karbonat"]We work with the analysis of alcoholic beverages, in particular - with vodka too. Firstly it seems too me that 96% purity - is too low for correct quantification analysis. But if there is no choice, do it according to established practice. There is an ASTM standard D 4307-99 (there are newer ones, but this is one I have) where the procedure of Standard Solutions preparation is established.
Now about your problem. As vodka contains volatiles, particularly 2-propanol usually in very low concentrations (1-20 mg/L absolute alcohol, AA), you can prepare standard solution only by dillution. So I can advice you to prepare a standard solution with 2-propanol concentration of nearly 5000 mg/L AA, then dilute it to nearly 300-500 mg/L 2-propanol concentration. Finally dillute the last one to receive extremely low volatile concentrations (1-20 mg/L AA). That's how we do it. It's clear, that you should dilute and prepare samples in 40% water ethanol solution.
BUT! Be attentive, initial ethyl alcohol always contain volatiles, in particular - 2-propanol (we take the puriest ethyl alcohol and the concentration of 2-propanol in it is usually in range from 0,5 to 3 mg/L AA. So don't forget to take this into account and establish the content of pure ethyl alcohol which you are going to use as a matrix for your standard solutions.
If there are any other other questions, don't hesitate to ask me.[/quot

Thank you very much.this is my preperation form.is it true or not?
İ want 100ppm stock and 10ml flask.i must take 1mkl propanol 2 purity 96 and dilute with ethanol.is it true?

[karbonat]

If you are spekaing about volumetric ppms, yes it should be 1 mkl in 10 ml for 100 ppm concentration. But you will certainly be faced with a problem, if you try to prepare stock solution in this way as it's impossible to add 1 mkl and record it's mass correctly.
I suggest you to do the following:
1. Prepare 40% water-ethanol solution (WES) by diluting ethanol with water. Let it stay for half an hour.
2. Prepare a Stock Solution (SS) #1 by the addition of 100 mkl of 2-propanol into 100 ml flask. It would be better if you pour 2-propanol into WES , otherwise 2-propanol will evaporate if you pour it firstly. Here you get the concentration closely to 1000 ppm.
3. Take 1 ml of SS#1 and dilute it with WES in 10 ml flask. It is a tenfold dilution, so the final concentration will be nearly 100 ppm.
Finally I suggest you to calculate mass concentrations too as volumetric preparation will not provide you results with accuracy, higher than that during gravimetric preparation. Volumetric ware is more likely than balances to be mistaken, especially when speaking about such low concentrations.
Feel free to ask me any questions here or contact via e-mail: Ethanol.Internal.Standard@gmail.com.