Chromatography Forum

Dear experts,

I will appreciate you help on this matter: when doing the suitability tests according to USP 35 401 (EPA-DHA in oils), to pass the nervonate-DHA resolution test has become an issue.

I use DB-WAX columns, and some columns pass, while others do not. Actually with some columns I am not getting two peaks at all. I have seen some peak elution orden reversal e.g. nervonate first, then methyl DHA

Is there a better option than DB- WAX to ensure consistent pass?

Care is always taken to adjust the gas velocity, etc due to column to column variability. After purging for 1 h, column conditioning is always done using a 10 °C/min ramp 40 to 250 and then 1 h at 250 °C.

many thanks

Dear jdelcm,

Throw out your old columns and purchase new ones. Do not bake for an hour at 250C at the end of every run. Turn your gas saver off. Use constant flow instead of constant pressure. You are over complicating things by trying to account for column to column variability. Check for leaks frequently. Check your instrument's flow control. The DB-Wax is fine.

Sincerely,
Keith