Chromatography Forum

I am having a lot of trouble with tuning my 1946D MSD Quad (ESI mose) and was wondering if anyone could offer some advice. My biggest problem is that the abundance of my high masses is nearly 0 which is causing the autotune to improperly adjust the peak width of the lower masses until the tune fails. If have tried adjusting manual tune parameters as described in the Agilent help files to fix this problem with no success. I have been successful in tuning the instrument in APCI mode but when I switch to ESI the check tune fails and I can not autotune. Is the problem with the spray chamber, the ion optics hardware (doubtful becuase of the ability to tune in APCI mode?) or the Tune settings? Sorry, I know the info here is minimal - I will be happy to add details, I just wasn't sure how much info to provide. Thank you for your help.

Paul

Since the tune process doesn't care whether APCI or ESI is used to create the ions it needs, I think you must be right to feel that the problem is unlikely to be ion optics. If you can autotune in APCI, it's also unlikely to be the settings for tuning. On rare occasions I have had our instrument get so far from a proper tune situation that the autotune cannot "find its way home", and under these circumstances it can be worth restoring factory defaults before running autotune. But I don't think this will help you. The settings after a successful APCI tune should be good.

One possibility is that your ESI tune mix has gone off. It is, after all, a different bottle to the APCI mix! I know it's expensive stuff, but you could buy a new one (store at room temperature; in the fridge there may be precipitation of tune masses).

Otherwise, yes, you would do well to check your ESI spray chamber is behaving itself. If the needle is partially blocked, it may be hard for the calibrant delivery system to force enough liquid through it to get a good spectrum. The heavier tune ions are usually weakest, and would suffer first. Make sure that when you pump into the spray chamber, there is a symmetrical cone of spray (shine a torch in one window of the spray chamber and look through the other).

an afterthought: if you've got some old tune reports (checktune or autotune) from APCI, from back when it worked in ESI too, have a look at these, and compare them to your recent APCI tunes. If the APCI signals have also got a lot smaller, it may really be an ion optics problem, but it's just become noticeable in the ESI results before the APCI.

Cleaning ion optics in the 1946 is quite do-able, but there are things that can go wrong, so I'd make this a last resort.

Looks like it was simply a bad electrospray needle. I was able to attach a second ESI source and the tuning passed. I will replace the needle in the old source and should be good to go. Thank you for your help lmh.

PK

Glad it helped. When you replace the needle, there are instructions on how to do it, and I think a video, in Agilent's CDs. If you're replacing the internal needle bit and keeping the same external part, the internal very fine needle sticks out about half its diameter (you should have a strange block of milled aluminium and a microscope thing to check and adjust this). Note that the fine needle is milled down to an even finer diameter at the end that sticks out. You have to get it the right way round; if it's the wrong way round, then half its diameter is too large a projection, and the spray will be awful. We once had a visiting engineer do this to us... it took a week to notice and correct.

When you've done it, have a look at your tune spectra, and make sure they don't have big spikes for no reason in between the proper masses. If they do, it probably means the spray is poor and droplets are flying into the MS at random points, generating sudden pulses of signal that the instrument interprets as a mass. This doen't necessarily stop the instrument from tuning, but it is horrible if you want to get a good spectrum from a chromatographic peak. It means an average spectrum across a peak is likely to contain spikes that are really just one-off noise events.

Good luck!