by
lmh » Wed Aug 18, 2021 11:34 am
(1) Collision gas: if your concern is provision of collision gas for the QExactive, don't worry about this in the context of the generator. It's going to use so, so little collision gas that you can provide high-quality gas from a cylinder, and one medium-sized cylinder will last you half of all eternity. The collision gas is totally independent of the gas supply for the spray chamber.
(2) Look very carefully at the pricing, including ongoing contract pricing. If you think Thermo are including maintenance of the nitrogen generator in their service contract, ask them again, and when they say yes, make them put it in writing, in block capitals, signed twice in indelible ink by their global managing director in the presence of witnesses. At least here, mass spec manufacturers happily sell Peak generators but always leave the servicing to be sorted out between you and Peak. What they say they'll do, when you're considering buying a mass spec, and what actually happens when you buy it, are potentially not the same.
(3) Peak generators used to be very cheap to buy, very expensive to service. I don't know if this is still the case, but check properly.
(4) Shop around, there are lots of companies able to generate nitrogen.
(5) If your lab is expanding, think very carefully about whether you want individual generators in boxes, or a fixed generator in a plant room. The boxed systems are easy, because you can just plug them into the mass spec and they can sit in a corner of the lab, but they have big disadvantages. They are noisy; not as noisy as they used to be, with better-designed casework, but a compressor always makes some noise, and it gets worse as they age; the internal compressor always exposes the remainder of the instrument to vibration, which shortens everything's life, no matter how carefully mounted the compressor is; you are paying for all that cladding, which is also a compromise between quiet operation and effective cooling, which also means the compressors run hotter than would be ideal. And you can't put the box very far from the instrument if you want to run 70L/min down a 1/4" tube - the pressure drop will be too big. You'll very soon find that you want your generators in a separate plant room because they're bulky and getting noisier, and then you'll need a fixed pipeline to carry the gas, and once you've done that, you'll find that for the price of two generators in nice cases you could have bought a single large, fixed nitrogen generation installation that has the combined capacity of eight of the nice generators in cases... and is cheaper to run and maintain. With the fixed installation you can choose whatever compressor you want, and have it mounted on a nice concrete floor that doesn't shake the generator to bits. Remember, also that as the compressors age, the working pressure and capacity tend to fall; I have no idea of the general level of optimism of the two companies you're using, but you are quite right to go for excess capacity. I would be very unhappy about relying on a nominally 70L/min unit to supply a genuine 60L/min demand reliably for a year.