Degraded cyano column

[tapira1]

We have two cyano columns and have run a mixture of four secondary and primary amines. Mobile phase is 50:50 MeOH: 10 mM H3PO4/Et3N pH= 3. Both columns are of the same brand and dimensions but one of the runs takes far longer than the other (in both cases peak shapes are excellent).
My question is (before running standard performance tests). Do deteriorated cyano columns in RP mode bind stronger or weaker the analytes?
Thanks in advance.

[Uwe Neue]

1. CN columns deteriorate much faster than C18 columns. Of course this depends on the use conditions and the way the CN columns is made, but I have seen 100-fold faster deterioration. Considering you are running amines, it appears that a higher silanol content on the older column should results in a larger retention.
You should consider using a silica HILIC column under the same mobile phase conditions. The retention could very well be similar to that of the CN column.

[tapira1]

Thank you for your prompt answer.
Have other questions if you could please consider to answer.
The cyano column is a Luna type, 5 um particle size, 250 x 4.6 mm. The most degraded cyano column has been previously used/stored under the following different conditions:

1- Used 4 hours at pH 6 (MeOH-30 mM phosphates); then washed (at least 1 h) and stored in 50:50 MeOH-H2O.

2- Used 4 hours at pH 3 (MeOH-10 mM phosphoric acid-primary/tertiary amine); then washed (at least 1 h) and stored in 50:50 MeOH-H2O.

We are not able to trace back when degradation took place (abruptly). My questions are:
1- Which condition was the most probable (severe degradation of column performance took place within days).
2- Is it safe to store cyano columns in MeOH-H2O?
3- Is it possible to attribute degradation to "unwashed" amine (Et3N, cyclohexylamine, etc).
Thank you in advance for your consideration.

[Uwe Neue]

Hydrolysis at neutral pH is a bot faster than at acidic pH. Best stability would have been around pH 4 to 5.

I do not recommend to store columns in an aqueous solution. I recommend to store in 100% acetonitrile. However, check the recommendations of the manufacturer.

Amines would have washed off the column. Even if they did not, they do not cause a pH shift of your storage solvent.