Chromatography Forum

Hi all

I am looking at an LC-MS method for S-sulphocysteine. There are limited publications on this and some inconsistancies in those that there are so I went back to square one. I don't seem to be able to get any retention with a pure standard using either a C18 Gemini or a ABZ+ using 50% ACN and adding 0.05% formic acid as suggested in one paper just made the signal disappear altogether in negative ion. I decided maybe making the butyl ester might give me a more retentive compound, so tried this last Friday pm - nice, first injection gave a good tight peak at 3.5mins RT, but wait the next, identical injection gave RT of 4.9 mins, then 7 mins and so on. Gave up friday but tried again this morning without altering anything and the RT of first injection is nearly back to original at about 3.8 minutes. Unfortunately the increasing retention time also comes back - the more injections you do the longer the RT.

HELP!!!

Is this unusual or am I missing something really obvious here?

Does anybody have any suggestions for the LCMS analysis of this compound?

Thanks

I would expect your compound to be unretained on a C18 in 50% MeCN. My recommendation would be to use a HILIC column.

me in the same boat as Geoff.

Trying to separate several s-contaning amnio acids without dev. on a C18 column using less than 10% methanol or ACN. Just tried phosphate buffer pH=7 with 10% ACN or metahnol, not working as stated in a couple of papers for general amnio acids (e.g. pH=7, 17% methanol). I used to use C30 to seprated several amnioc acids including cysteine and methinione, it worked.

Any help is very much appreciated.

Yep I was beginning to come to the same conclusion about HILEC being the way to go, I was interested in the odd behaviour of the repeat injections.

Thanks