Chromatography Forum

Recently, our analytical group has been trying to find ways of improving solvent shelf life. I have been researching additives to solvents to prevent bacterial growth and by consensus adding 0.02% of Sodium Azide is sufficient to inhibit bacterial growth. The papers I found, however, were using UV detection and had no information about effects of the solvent on a Mass Spec. I was wondering if anyone has had experience with the use of Sodium Azide in the mobile phase and used it with a Mass Spec or if anyone could point me to some literature that has this information?

Hello

What solvents you want to "protect"? Sodium azide is good for high water-content mixture (buffers).
I'd check amber bottles first and check stability of mobile phase after 2, 3 days and week after (if you prepare more than 5 liters).

Regards

Tomasz Kubowicz

We are looking to preserve our 5mM Ammonium Formate solutions. We know Sodium Azide is a good bacterial inhibitor but we want to be sure there are no adverse effects to our MS before we start using it in our mobile phases. Has anyone used Sodium Azide in their mobile phase and had it run through their MS? If so, where there any adverse effects to the MS?

If you have previously done any significant amount of LC-MS work, you will have already seen spectra with [M+H] AND [M+Na] & [M+K] signals. These latter are derived from the glassware. If you are trying to identify unknowns these extra signals are often very helpful in determination of MW. If you are doing quantitative work, these additional signals detract from the ion current that could be carried by the [M+H] ion.
If you run at 0.02% sodium azide,
1) you risk this salt plugging capillaries or sprayers,
Depositing on source metal components & tuning lenses, which will degrade the tune and diminish sensitivity.
2) You will likely see ONLY the [M+Na] and [M+K] signals.
These are virtually impossible to fragment by MS/MS, so no structural info out.
I would not go near it !

Thank you for your response!

We are looking to preserve our 5mM Ammonium Formate solutions. We know Sodium Azide is a good bacterial inhibitor but we want to be sure there are no adverse effects to our MS before we start using it in our mobile phases. Has anyone used Sodium Azide in their mobile phase and had it run through their MS? If so, where there any adverse effects to the MS?

Will your methods work if you add 0.1% Formic Acid to the mobile phase? I have used it in most of mine and so far have not seen bacterial growth, even when I have a partial bottle I leave sitting on the counter for weeks before dumping it.