Quadruple Mass Spectrometer - Transition metal detection

We use a QMS in our vacuum chamber, mainly for residual gas analysis. In a recent project I tried using it during the an argon sputtering of carbon infested Ni(111). I got a lot of carbon- hydrate peaks but to my surprise no Ni peaks up-to 200 AMU. I tried firing the Titanium sublimation pump, to saturate the environment with Ti. No peaks again. The QMS has 2 detection mode. one chaneltron and a farady cup. Is there a fundamental reason for not detecting any signals for Ti or Ni?