Page 118 - Inorganic Mass Spectrometry : Fundamentals and Applications

I08 Olesik

5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85
Mass

...........

...........
c.
U)
n,
...........
m
c 104
.-
CIC)
U) 103
.-
Q
102
101
E O
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Mass
15 ICP-MS background spectra (plotted on a log~thmic scale) for a sample
containing 0.1% nitric acid: (a) Conventional plasma conditions (l000 W, 0.77 L/min
nebulizer gas flow rate). The h+ and O+ signals are saturating the detector, so their signals
are greater than 2 X 109 countslsec. (b) “Cold” plasma conditions (600 W, 1.08 L/min
nebulizer gas flow rate). Note that full scale in (a) is 1010 whereas in (b) it is lo8. (From
Ref. 14’7.)

Collision-~e~ction Cells. Perhaps the most exciting development regarding
molecular ion removal in ICP-MS is the use of collision or reaction cells, intro-
duced in Sec. 3.1.5. These rf-only quadrupole, hexapole, or octapole cells, typ-
ically operated at pressures around 10 mtorr, can provide two benefits: The
collision cell can be used to reduce the ion kinetic energy and to focus ions toward