Hi,
Recently i have run into a issue with my Se_78 CCV. In our lab, we analyze drinking water for 24 different parameters and our CCV has 50ppb of each parameter in it. Our mass spec 7900 is set up with a ISIS and a SPS4 autosampler. We use Sc, In and Tb as our internal standard. Se is the only analyte we scan for using H2 mode, the rest are done in He mode.
Lately, our Se CCV starts to drift as the run goes on. It starts out at 50ppb and then continues to decrease, always down toward 40ppb, never up. I have tried making the CCV from a fresh stock solution, different cal stds, different internal standard stocks. Samples are scanned in triplicate and RSDs are always below 3%. Any help or insight would be appreciated.
Thank you,
Cory