Chromatography Forum

hello every body,

I'm kind of new to the world of LCMS, i start working on a thermo LCQ, after the first 3 months of usege I change thye oil on the vacum pump and since then the ion gauge value is stay fix at 1.20, while before was fix on 0.80.

what would be the ideal value for the ion gauge on a lcq? what could be the cause of such a variation?


thanks,

Matteo.

Our LCQ DecaXP is currently at 1.6*10^-5. According to the TunePlus help-file it should be approximately 2*10^-5. It will vary slightly with how good your rough pumps are, and how much solvent there is in their oil(!), but varies mostly with whether the ion transfer capillary is open (ready for action) or blocked with a spare APCI needle as most engineers suggest you should leave it between runs (to avoid it vacuuming in all the rubbish in the lab). It will also be low if, the last time a new ion gauge was fitted, the engineer didn't manage to tighten it enough (depending on the exact model you have, the gauge's fitting varies from "difficult-to-tighten" to "completely-impossible-unless-you-are-a-double-jointed-orangutan-with-thin-wrists". A slight leak very close to the gauge gives a higher reading.