Loss of peaks and sensitivity

[sally]

Hi,
Could anyone help me with the following problem. I am using the Micromass Quattro Ultima and I am working on the development of a method for malachite green and its metabolite leuco malachite green.
I am using acetonitrile and formic acid/ acetate buffer in my mobile phase.
After I leave the system idle, for a few hours, the first injection contains all transitions that I am looking for at a sensitivity that I can work within. However in subsequent injections the sensitivity drops by a factor of at least 20.
Could anyone throw any light on this subject as I am in a bad need to feel like this and I am thinking of changing careers at this moment.
Thanks a million

[Uwe Neue]

Subsequent injections of standard, or real sample? Isocratic or gradient?

[sally]

Thankyou for your reply, it occurs while I inject the same standard (not working with samples yet). I am using a gradient.

[Uwe Neue]

I think I will change my career with you.

I suggest to separate LC from MS issues and run the same experiment with the LC attached to a UV detector. If it happens then, I would chase issues with the injector. If not it is the MS.