separation of positional isomers of fluorophenyl acetic acid

[praveenpaliwal]

I am working on separation of positional isomers of fluorophenyl acetic acid. It has 3 isomers . 2-Fluorophenyl acetic acid, 3-Fluorophenyl acetic acid and 4- fluorophenyl acetic acid. How we can separate these isomers on RP-HPLC and C-8 or C-18 columns . Or any other HPLC method to separate these isomers or there should be use of some specific column

praveen

[Uwe Neue]

What have you tried? A change of pH might help...

[praveenpaliwal]

I tried the acdic mobile phase near about 3.35 pH with tetrabutyl ammonium hydrogen sulphate with methanol as a organic modifier , any other method for separation ??????

[juddc]

I ran across this and thought I might suggest a look:

http://www.phenomenex.com/lib/5076_I_Lu ... ochure.pdf

Please note that I have not ever used this column or any one like it and I am not in any way associated with the vendor, but selectivity on this one looks interesting.

[SIELC_Tech]

All three compounds have slightly different Log P and Log D and you can use this in mixed mode separation. You will use reverse phase and anion-exchange mechanisms to separate these compounds. We never tried this mixture but have another example for this type of separation:
http://www.sielc.com/compound_221.html
Here are few other examples when isomers are separated by mixed mode mechanism (reverse phase and cation-exchange, reverse phase and ion-exclusion)
http://www.sielc.com/compound_287.html

http://www.sielc.com/compound_216.html

http://www.sielc.com/compound_187.html

Please contact me if you need more information.

Regards,

Vlad

[Uwe Neue]

If I understand you correctly, you only have the described components in your mobile phase for the method that you have tried. My suggestion would be to add phosphoric acid to change the pH and see if the change in the pH has an influence on the separation. In principle it should, if the pKs of the analytes are sufficiently different.

My concern is that with the addition of the ion-pair reagent, you have moved into the direction of ion-exchange, which is not that sensitive to changes in the hydrophobicity of your analytes. I would have started to play with pH without the ion-pair reagent.

[praveenpaliwal]

[quote="Uwe Neue"]

I got your point and I am also trying to analyse on low pH like 2.5 or 2.2 .
So mobile phase is
A=[MeCN + Methanol ] : B= Water [ 0.05 M KH2PO4 , pH 2.3 by H3PO4]
The ratio of A : B is 30 : 70 , Please seggest me if I am giong in right direction

Thanks and regards

praveen