Chromatography Forum

I've been seeing sporadic growth of an impurity as samples are waiting for HPLC analysis. I've just gotten MS/MS results from this impurity and it is +27 mass units, and shows the addition at an active carbonyl. I believe this is nucleophilic addition of CN from HCN or CN ion present at trace (20ppb) levels in my acetonitrile.

Has anyone else ever experienced this, and if so how did you overcome the problem without abandoning acetonitrile?

Can you dry you samples then re-suspend them closer to the time of injection?

Preparing each sample at the time it will be injected is likly to help significantly, but it's very impractical given the number of samples and method run time. What I'm looking for is a simple method to test the ACN for trace cyanide, or a process that will reliable remove any trace CN.

As I understand the commercial production of ACN it primarily comes from the waste stream of acrylonitrile production. HCN is also part of the waste stream and I expect the clean up is not consistently removing the HCN.

Outside of this forum a friend shared a similar story. They overcame the problem by switching vendors. As I looked into that none of the vendors I've found are controlling CN content. The typical explanation is the solvent must meet ACS reagent grade, which doesn't call for cyanide testing.

One thought I've considered is vacuum degassing. HCN boils at 26C, so it seems I should be able to reduce / remove it this way.

Thanks for your suggestion, it's a good one.

Oooo vacuum degassing is a good solution, very clever mate!

Good Luck.

Luke