Agilent Technologies 5975 Operation Manual page 116

4
Operating in Chemical Ionization (CI) Mode
Methane pretune after more than a day of baking out
Note the low abundance of m/z 19 and absence of any visible peak at m/z 32.
Your MSD will probably show more water at first, but the abundance of m/z 19
should still be less than 50% of m/z 17.
116 5975 Series MSD Operation Manual for MassHunter