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A case to eliminate retention time drift in ANP using the Cogent Diamond Hydride in LCMS.

Reference Number: AA-04067 Created: 04/14/2020 01:00 PM Last Updated: 09/18/2020 03:38 PM

We had a significant  run to run RT drift ( up to 1 min for 10 repeated runs) using the Cogent Diamond Hydride™ HPLC column we ordered two weeks ago.  After conditioning the column with  90% IPA and 10X  1% phosphoric acid injections as suggested for our specific method, we were able to see our compounds of interest. However, we could not get reproducible retention time in repeated sample runs with our sample matrix. I have tried extending the aqueous wash to 20min, still no help. Do you think this is due to our LC or column problems?

Mass Spec: Negative ion
Flow rate at 0.6 ml/min
Column temp 40° C
Solvent A ; 50% water / 50% isopropyl alcohol /  0.025% acetic acid and 5 uM EDTA
Solvent B : 10% water / 90% acetonitrile with 5 mM ammonium acetic with 5 uM EDTA adjusted to pH 7.0 using NH3
Injection volume: 2 ul
Sample dissolved in 50% acetonitrile/ 50% water 0.2% ammonia

T0           99%B
T1           99%B
T15         20%B
T15.1           0B
T29              0B

Stop: 29 minutes
Post: 7 minutes

I don't think this is a column issue. The mobile phase is similar to one I used in the vitamin separation (ammonium acetate in the B solvent, acid in the A solvent). I did notice retention drift issues if the column was not thoroughly equilibrated. Maybe you should try having the gradient not go all the way to 100% A. That way there is always some ammonium acetate in the mobile phase. I think the ammonium acetate takes some time to load and remove from the column. If there is always some ammonium acetate around, it will not have to be completely removed and then re-adsorbed on the surface for the next run.

I think column may need 30 minutes more conditioning with solvent A (50% DI water/50% isopropanol), before use.

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