Chromatography Forum

I am detecting taurine via LC/MS/MS (QTrap) in ESI (-) 124-->80. Mobile phase is 20mM ammonia acetate (A) and ACN (0.1% Formic acid, B). The strange thing is that once the taurine sample was injected , the carryover is huge. I injected 1ul 1ug/ml (thus far, just tried standard). Later on, the blank run will get even higher taurine peak. Had thought that maybe it is due to the mobile phase contamination. Tried to change buffers (prepared all fresh solvents. changed the gradient) and use other columns. One time, after using freshly prepared mobile phase to wash the system (including the column) for several hours, got residue taurine to a acceptable low level, however, after the taurine standard's injection, the taurine peak will still be there for a long long time. --- indicated that it is not the contamination. No idea why the taurine peak (I also set positive ESI MRM there, and confirmed it is the taurine peak) is always there. Any comments will be welcome. Thanks.

1) What type of HPLC System? (if Shimadzu, try adding formic acid to the wash solvent, wash before and after, and set purge volume (i think that's what its called. it's the first line in the autosampler conditions) above 450ul).

2) what type of column?

3) Try lower concentration of taurine (500ng/ml, 250ng/ml, 125ng/ml) and inject starting with the lower. See if you can minimize the carryover and verify it changes with changing concentration. Can you try changing the Q1 and Q3 to High resolution to minimize the window (make sure they are calibrated for High)?

4) Try an MS3 experiment, and a precursor experiment. Keep your windows narrow so you can see the interference through the noise.

5) These new instruments are so sensitive that you see things that you couldn't see bfore and weren't expecting!

Below are LC-ELSD for taurine:

Unison UK-C18: http://www.imtaktusa.com/site_media/fil ... TI227E.pdf
Unison UK-Amino: http://www.imtaktusa.com/site_media/fil ... TI360E.pdf

Sorry I forgot to add

have you tried injecting sample an then blank without the column?
That should quickly tell you if it's the column or instrument
if instrument - the usual suspects: needle seat, autosampler , sample loop , ect