Chromatography Forum

I have two analytes (aminoglycosides) with different precursor and product ions eluting at the same time.. When i have high concentration of one of those analytes (around 2ppm in vial), i see some signal peak in the the transition of the other analyte too.. Am not sure if i have to call this as crosstalk.. But, Is it common to have such phenomena while working at high concentration? or if they fragment in the same way?

I made sure its not contamination while preparing standards or carry over between LC runs.. and am using Quattro micro MS.. I use interchannel and interscan delay as 0.02sec..

To make sure, could you just put some other transition between the two that you want? This will insulate one from the other and completely exclude crosstalk.

Agree with Imh.
Anyway, classical cross talk is observed when actually 2 or more related compounds are coeluting and are present in higher concentrations (as you said), and share the same product ion in the individual SRM transitions. Usually this effect is more pronounced when you use lower dwell time between each SRM transition, thus making possible the product ions from the previous SRM transitions formed in the collision cell to be scanned out during the following SRM transition.
The possibilities that you have at the moment are:
1. To improve the chromatography - separate the peaks of the related compounds
2. Lower the concentration of your standards/samples - not to overfill the mass analyzer with ions from the previous SRM transitions
3. If separation is not possible - use specific SRM ion transitions for every eluting compound that will be different from the other compounds - if possible.
4. And normally after all these changes you should check the cross talk using standards with only one compound, but monitoring all the SRM transitions for which you're interested. Appearance of peaks in the other (related compounds') transitions will indicate a possible cross talk.

Good luck.

Dear all,
One easy to check for cross-talk is to increase the interscan delay. If signal disapear while interscan delay increase, you have cross-talk.
Did you check that each standard is not polluted by each other?

Kind regards,

I agree with the methods outlined. Increase the inter scan delay or put in a dummy ion/transition between the two analytes for a few 10's of milliseconds (maybe 100 msec or so) worth of scans. If it is cross talk it shoud disappear. If it does not, something else is causing your problem.

Alp

Thank you all for the valuable suggestions ..
I managed to minimize the crosstalk by chromatographically separating most of the analytes and working at lower concentrations.. I didnot increase the delay times and dwell times as it reduces the number of points in the peak and decreases the sensitivity.