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- Posts: 12
- Joined: Fri Mar 30, 2007 7:46 pm
Without going into too much detail (it’s a VERY long story), we’re over 4 months into the purchase and set-up of a “refurbished” Waters LCT Micromass Premier XE and we’re still in the set-up phase of this process. As you can guess, my boss is NOT happy….
I *finally* got signal (peaks! big beautiful peaks!) over the weekend but I couldn’t help but notice the masses were not what they’re supposed to be. I will be doing all of my analyses in negative mode (oligonucleotide analysis), so I’ve focused primarily on the negative calibrants (sodium formate, sodium cesium iodide). I’ve also used Waters’ very expensive Leucine Enkephalin standard. When I inject the Sodium Formate calibrant via syringe (flow rate = 10-20uL/min), I see peaks at 110.6, 177.1, 243.7, 310.2, 376.7….on up to 1708.2. I believe our 376.7 peak must be the formate cluster that should be present at m/z = 384.91—a full 8.1amu away!
Unfortunately, things only get weirder. The amount of error we see is proportional to the mass: for every 100m/z, our error increases by about 2.1 amu. the 112.98 peak appears at 110.6 (2.38amu lower), our 248.94 peak appears at 243.7 (5.24amu lower), and our 384.91 peak appears at 376.8 (8.1amu lower).
I have a bit of experience running oligo samples on a very well behaved, brand new Agilent 6530 but I never really had to do much optimization of the various voltages: the Agilent was installed and the ionization parameters worked great for over two years. Now, at this new job with this new (old) Waters instrument, I’m having to learn as much as I can as quickly as possible, though the manuals are only so helpful. They don’t explain what the various voltages physically do, so I can’t predict how altering a parameter will affect the spectrum. The used equipment company isn’t any help and I found out that Waters considers us a competitor (I have absolutely no idea why), so we can’t get a technician to help. If anyone can provide any hints as to what parameters I should focus on, I would be incredibly appreciative!