LC-MS peak shape

[MIB_EO]

I'm trying to do some exact mass work on a Waters LCT. The calibration and lockmass peaks are all fine and when I run standards I can get a mass accuracy < 10ppm.

However when I run samples (peptides etc) a lot appear with a tailing peak (MS not LC) shape. This seems to cause problems in the centering process so that the mass error is 10-50+ ppm.

Anybody any ideas on the cause or preferably remadies? What other information would make a difference?

[Ary]

Not sure I fully understand what you are seeing but a couple of things to note. LCT should be capable of <5ppm on standards. For the samples try injecting less sample. If there is too much then the masses shift slightly. Alternatively try measuring the exact masses at the end of chromatographic peaks. If as I suspect you have an older version then these suggestions should help. If you have the latest model and software then I thought these were addressed automatically and I'm stumped but you should be covered by warantee and a quick phone call to te factory should sort you out

[james little]

some information on earlier LCT accurate mass at

http://users.chartertn.net/slittle/acc.html

and in particular in an ASMS poster presentation..

http://users.chartertn.net/slittle/file ... adtime.pdf