Page 79 - Inorganic Mass Spectrometry : Fundamentals and Applications

~nductively ~oupled Plasma p ass Spectro~et~ 69

entially pumped interface, ion optics, a mass spectrometer, and a detector. Ioniza-
tion efficiencies in the plasma are nearly 100% for elements with ionization
potentials less than about 9 eV. However, only about 1 in lo4 to l in lo6 atoms in
the original sample are detected, so extensive loss of ions occurs during their
transport from the plasma to the MS detector.
The sample is typically pumped at a rate of 0.4 to l .O mL,/min to a nebulizer
that produces an aerosol with a range of drop sizes from submicrometer to 40 p,
in diameter [4,5]. Recently, nebulizers with small dead volumes that can be used
with sample uptde rates as low as l0 p,L/min have been introduced. The aerosol
is modified as it passes through a spray chamber. Most aerosol drops that are too
(>20 pm diameter) are eliminated
large to be vaporized effectively in the plasma
in the spray chamber. The spray chamber also limits the total amount of solvent
liquid aerosol and vapor that enters the plasma. The aerosol exiting the spray
chamber enters the hot, atmospheric pressure plasma gas (typically argon).
Each aerosol drop undergoes a series of processes (Fig. 3.2) in the hot
plasma. The solvent evaporates from each drop, leaving a particle. The particle
vaporizes and is converted into atoms and ions in the plasma. The atoms and ions

Detector I
Detection
Quadrupole Mass
filtering
r-i- Ion
Ion Optics II focusing
I I
Charge separation
Skimmer \ ,+
\/
Sampler Gas sampling
Diffusion
Free atoms, Ionization
ions
Atomization
Vaporization
Particle
Desolvation
Droplet 0

ure 2 Series of processes a drop of sample undergoes in the ICP to produce ions,
some of which are transported through the sampler and skimmer, focused into the mass
spectrometer, filtered on the basis of their mass-to-charge ratio, and detected.