Yes, a modern single quad should be able to resolve isotopes. Halogen-containing compounds are easily resolved. As mentioned by Dr. Irei, the sensitivity of the system limits the detection of some of the less common isotopes.

Hello Fatima, I concur with Satoshi and Jack, that different in mass is easily detectable in a single quad, although I am worried about the resolution.  If you would like more sensitivity, you can run SIM (Single Ion Monitoring) mode, where instead of the quadruople 'scanning', you set it for a particular set of  masses (in this case 36, 38 and 40).  The quadrupole will only look at these masses and not the whole range, and you will get greatly enhanced sensitivity.  In fact you will probably have to dilute the Ar[40] if you are trying to run them all in the same experiment, but SIM mode is an excellent way to get more sensitivity, especially from a matrix.