[mercenary_sg]

Hi, i am new here. Now stuck with an assignment. Hope u folks ard here can help me.
Ascorbic acid, at diff pH, it will have different Lamda Max. So if i were to find the concentration of Ascorbic acid in any products, eg like Cough Syrup, then how do i do it.
I heard that the pH can be controlled before using UV-VIS to get the abs reading. How do i do it.
The method i am gonna use is Standard Addition Method to determine the concentration.

So if i were to set my pH for Ascorbic acid at pH 2 where Lamda Max is 245nm, then my cough syrup, how do i dilute my cough syrup to get the ascorbic acid to adsorb at 245nm?
Please help.
Thank You

[FeLiXe]

you set your pH to 2 by using a buffer solution. then your absorption max is at 245nm. you might need to dilute your solution to get into the best absorption range.

if you don't want to change the pH you could also measure at the isosbestic point if it has a good extrinction coefficient

[mercenary_sg]

Hi, thanks for your reply
But for isosbestic point and good extrinction coefficient, where do u suggest i get them, if eg like i am to test cough syrup for the concentration of Ascorbic acid, there is bound to be multiple compounds in cough syrup, and they might have the same molar adsorptivity, if so, what should i do.

[FeLiXe]

if you don't want to look into literature you can try things out with your standard.

take a spectrum of the alkiline and acidic form with the same concentrations. where the lines cross is the isosbestic point.

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if you are worried about impurites it is probably better to go with a buffer and set pH 2.

for your standard addition you could look at several wavelengths and compare the results. then you will notice if one extinction was changed because of impurities

[ARGOS++]

Dear mercenary_sg,

Why not using MCA, Multi Component Analysis, in a buffered Medium (e.g. buffered Water),
correct designed, it does ALL, and a LOT MORE for you, - automatically!

For more Info:    "Multi Component  Analysis (MCA/MKA):"

- "a LOT MORE ": = Quality Control  &  Reliability  &  Std. dev  &  SST  &  . .

Good Luck!
                  ARGOS⁺⁺

P.S.: There is also Help for Buffer-Problems on that Site!