I have a question about tuning a LCMS. Is it normal to have a shift in mass, when you keep all your tuning parameters and analyte constant. If it is normal, how often do you see this? Is this a sign that the cone might be dirty? Thanks a lot.

How much shift are you seeing, over what time interval? Over time, it will shift, and eventually you'll have to recalibrate your mass axis with known mass standards (usually supplied by your instrument manufacturer).

Its about ~7m/z difference. It's that I was
optimizing the tune page and noticed that the
same analyte that was showing ~931m/z is
now showing 938m/z. Its been about a
month's time between these 2 readings, but
the LCMS was hardly used. Thanks for any
kind of advice.

7 m/z? Wow, that's a huge difference. If that really is the same compound, then it could indicate a serious problem. How is your resolution? How is the sensitivity?

Try infusing the manufacturer's mass calibration solution, and running their calibration routine. Often there will be a way to check the performance without changing anything, and a separate routine to automatically or manually calibrate the mass axis and resolution. If the check routine shows that your masses really are that far off, you could try to calibrate it. Be sure to save a copy of your old calibration file (tune file, instrument data file, whatever they call it) before doing this, if possible, or a hardcopy printout with all the parameters.

If you can get some free phone support, it wouldn't hurt to call the manufacturer and see what they think.

What type of molecule are you analyzing? My guess is that it is a multiply-charged ion, specifically a triply-charged ion. The original peak at m/z 931 was [M+3H]+3 and the ion now observed at m/z 938 is [M+2H+Na]+3.