dose UV detector in LCMS have worse UV noise

[jiangds06]

does additional MS increase noise of uv detector?

[lmh]

No. You can attach the PDA and MS in various ways; in general people put the PDA and MS in series (PDA then MS, obviously), and if this is the case, the PDA will experience slightly higher back-pressures, which should not affect it in any way. If you put them in parallel, then the PDA will receive a lower flow than it would alone, and this can mean that there is some increased peak-broadening (analyte peaks going down the PDA leg of the split post-column will move more slowly than they otherwise would, so they have more chance to diffuse out) - and increased peak-broadening will show up as worse signal:noise. But this is decreasing signal, not increasing noise.