I been having issues recently with the reliability of my system (allience 2795 and Quattro ultima) and have spent the day trying to isolate what the issues might be. I've mostly been performing single injections (of a standard solution of 4 compounds), altering and noting the effects of various RF1 setting and desolvation flow rates etc and I've been having no problems at all. Then I run 7 samples in a row, an emulation of my assay samples (2 uM of a reference compound and seven different compounds (one per sample) also at 2 uM). The first two runs were fine (peak area/height) but then the peaks started becoming less intense so by the 5th sample I've near enough lost the peaks altogether. After much brow beating I've identified how the issue manifests but not what the problem is. If I run 7 samples in one batch, after the first sample the peaks drop dramtically in height/area, however, if I run each sample as an individual batch, one after the other, the peak height/areas seem to be fine.

So there must be a routine the Needle/injector goes through but only at the start of a batch and not inbetween samples within a batch......and I have no idea what that might be. Is the wash/purge cycle different? Does the needle prime itself differently at the start?

Has anyone had a similar issue who might be able to point me in the right direction?

Thank you