MS Question

[sanks086]

hello,

I am currently running a general LC/MS method and have a problem. It is long been known that my nitrogen generator is slowly dying and therefore I am unable to get any drying gas flow of greater than 5L/min. This is obviously not allowing me to optimize my MS sensitivity and therefore is frustrating. Has any one else had this issue? How did you resolve it? Thanks. PS: My company has decided that fixing it through the manufacturere would not be cost effective. Thanks.

[sam.pedraglio]

If the fixing is not cost effective, replace it.
Otherwise you have two choice:
1) use nitrogen bottle, depending on your ms method, a bottle could survive for one, one and a half working day.
2) use a central liquid nitrogen container and distribute the nitrogen around your department.

[lmh]

We had this issue because we bought our nitrogen generator from a particular firm who shall remain nameless, who have outrageously expensive service arrangements, and whose product collapses too quickly for words.

We had to buy a different nitrogen generator, from Domnik Hunter, who offer a very sensibly priced service contract.

It is ridiculously non-cost-effective to run a very expensive LC-MS system with inadequate drying gas. At the very least, you will lose a huge amount of sensitivity and potentially have spray-chamber corrosion problems. In money terms, it means you are either storing up maintenance issues, or you are wasting money because you could have bought a cheaper machine and maintained the nitrogen supply! Installing a liquid nitrogen system works, but is far from cost-free. Nor are cylinders.

Having said that, there are things you can do:

Anything you do that reduces the liquid flow into the MS will reduce the amount of gas you need. Reduce column diameters, split the flow before it gets to the spray chamber. Reduced column diameters and reduced overall flow saves solvent, but can be problematic if your hplc system has a big dead volume. Splitting is helpful if your hplc isn't up to low flows.

But remember, your gas generator will eventually collapse completely, so unless you're prepared to go as far as nano-flow (where sometimes no gas at all is needed), sooner or later the current decisions will catch up with you.