Our 7900 ICP-MS is showing high oxides/doubly charged upon start-up. Running the standard lens tune, plasma correction, and resolution/axis typically fixes the issue and brings the ratios down to something reasonable.
To illustrate, the full-suite of start-up procedures was run yesterday (our routine practice, performed monthly) which yielded oxide/DC at 1.36/1.19%, and then several standards and a few drinking water samples were run. Today, just running the performance report (and no other start-up procedures) yielded oxide/DC at 6.29 and 1507.06%. Running the standard lens tune, plasma correction, and resolution/axis brought it back down to 1.37 and 1.27%.
This is atypical, and has only been observed in the recent past. I'm wondering if this could be indicative of a hardware issue?
Replacing the cones did not fix the problem. However, cleaning the lenses, which were quite tarnished, has fixed the issue. Performance reports are consistently good between runs, and it isn't necessary to run the plasma correction upon every start up. So the issue was a hardware related one.