Sugar Analysis with Anomaous Peaks

[Omar]

Hi All

We are running a chromatographic system involving mannitol and sorbitol on a column from Machery-Nagel: VA 300 7/7 Nucleogel Sugar 810 Ca 300 x 7.7mm. Please find attached chromatogram.

Separation conditions are as follows:

Column Temperature: 85C
Mobile Phase: Deionized Water
Flow Rate: 0.5ml/min
Detection: RI
Injection Volume: 20uL
Conc of Solutions: 50mg/mL

As you can see from the chromatogram the peaks are observed to front anomalously.

Could you help us on this issue?

Thanks for your co-operation

[Bryan Evans]

Couple things could cause those peak distortions:
1. Column Void
2. Column fouling
3. Injection of strong sample solvent (if sample is dissolved in organic)

You can try contacting the column manufacturer and see if you can turn the column around and pump m.p. in the opposite direction. If the void is near the outlet frit - this will help (be careful, some columns can be damaged by this). This may also help if particles are clogging the inlet frit.

you might also want to evaluate sample cleanup.

Imtakt has a great column for this - sugar alcohols are easily separated on Unison UK-Amino:

http://www.imtakt.com/TecInfo/TI313E.pdf
http://www.imtakt.com/TecInfo/TI358E.pdf

[tom jupille]

The fact that you have similar anomalies on both peaks suggests either a void space or partially-plugged frit.

I'd follow Bryan's suggestion and try running the column in reverse.

[Omar]

Thanks for your help,
I think you were right it was a void volume problem, because we've tried a new column under the same conditions and it worked out fine.
I will now try to solve the problem with the other column by running it in the reverse direction.