Chromatography Forum

Dear All,

Our lab is considering the acquisition of a LC-MS instrument. Some vendors insist that a N2 generator is required for some instrument operations and or configurations. Others say that N2 cylinders can be enough.

Could you comment on this?, what ionization modes or instrument configurations required a high N2 volume to operate?, and what could be the relative advantages of N2 generators over other sources?

Thanks,

josebenjamin

Find out from LCMS supplier how much nitrogen per minute is required. I'll bet nitrogen cylinders won't last very long, liquid nitrogen cylinders used more often. However, nitrogen generator is least fuss of all.

Jose,

1. Liquid N2 tanks in the lab.are bulky; sometimes are delivered at less than full !!!! and the gauge that indicates the

2. N2 cylinders are a pain in the neck to move around in a restricted space, and therefore are potentially dangerous due to their weight.

Probably the two best options are

(a) a N2 generator of the type sold by Whatman (compressed air IN and N2 OUT @ 95-99% purity depending on flow rate). Separation is by diffusion through a disposable filter, changed 1-2X per year. Silent operation, inexpensive; I have used for years with TSQ and LCQ systems.

(b) Liquid N2 plant outside the building to pipe N2 gas to lab.

I would recommend (a) if you already have a compressed air line @ 100-120 psi into the lab.

JMB

JMB

ESI takes about 500-1000ml/hr N2 flow as desolvation gas. Nano-flow techniques use less, Mega-flow more.

Purity of gas isn't too much of an issue 99+ should be fine. Cylinders are heavy and a bit of a pain - they CAN be suitable, it depends on how many samples you are running.

N2 generator needs to be at higher pressure than some systems produce but there are several that can produce the 50-100psi required.

the least fuss is a building supplied external tank, piped in, that somebody else has to maintain!

Another option is a liquid nitrogen dewar. They come in several sizes. We use on that is about 220L with a 235 psi safety valve. The MS manufacturer will be able to tell you how much nitrogen you need. If a dewar will last a week for you, that would be a convenient, reliable and clean source of nitrogen.

Dear Friends,

Thanks to you all for your thoughtful comments. They have been very useful.

josebenjamin