I have problem with analysis beverages

[Perica]

Dears,
I am working on HPLC system with PDA detector. My field work is beverages (nonalcoholic drinks).

Question is:
Analysis of additives and vitamines in soft drinks were excellent on Column Varian C18 250mm x 4.6mm

Now I work on ChromSep HPLC column SS 250 x 4.6mm Incl. holder with ChromSep guard column ChromSpher 5 C18

Analysis (Na-benzoat, K-Sorbate, Citric acid, Absorbic acid) on this column are bad. Only coffeine analyse is OK.
Mobile phase: 80% KH2PO4 0.025M, pH4.5 + 20% ACN
Flow rate: 1.3ml/min
Wavelength: 235nm
Mode: Isocratic


Do you have any suggestions? Maybe different mobile phase or something else.
Do you have application notes for these kind of analysis on this type of column (without ion-par reagense)?

Thank you and best regards

[Uwe Neue]

The method is not very good. You are working with phosphate at pH 4.5, where it has no buffering capacity whatsoever. Adjust the mobile phase pH to either around 3 or around 7! You peaks will move around somewhat, but the tailing should go away.

[WK]

Dear Perica
Yes,
Years ago there were a lot of beverage methods out there using unusual buffering - most of which would not give reproducible chromatography.
I think now there are many better methods available. You may have to have two methods - one for additives - one for vitamins.
I would stick to low pH work if you can.
I don't think its possible to have one method unless you have only one characterised sample to analyse.
Best Regards

[tom jupille]

If you have a method that works consistently on a particular column, why change?