Page 128 - Inorganic Mass Spectrometry - Fundamentals and Applications

118 Olesik

for light analyte ions. As a result, detection limits for light elements in a sample
containing high concentrations of heavy elements are degraded significantly,

~~~s~ectrai Chemical Matrix Effects
Changes in sensitivity (sign~concentration) can occur in ICP-MS, depending on
the identity and concentration of elements in the sample solution and the solvent.
Chemical matrix effects can be due to changes in the analyte transport efficiency
from the nebulizer into the plasma or modification of ion generation in the plasma.
The severity of this matrix effect depends on the concentration of matrix ions
generated in the ICP, not the mat~x"to-analyte ratio. Wenever the matrix ion
current becomes significant compared to other ion currents, matrix effects are
observed [144]. Therefore, sample introduction systems that increase the sample
transport rate into the ICP suffer from chemical matrix effects at lower dissolved
solid concentrations in the sample.

~atrix Eflects Originating in the Sa~ple Introducti~n System. Solid stun-
of
ples are often dissolved by using acids. Variations in the concentration and type
acids used can result in both transient (over several minutes) [l471 and steady-
state changes [ 168,1491 in analyte sensitivity due mainly to processes that occur in
the spray chamber. Fortunately, the acid-dependent changes in analyte transport
efficiency are typically less than 20% unless the variations in acid concentration
ver, significant changes in sensitivity can occur as small initial
are added [ 1701. Furthermore, the severity of the acid effects can
be dependent on the nebulizer gas flow rate. Large v~ations in iss solved solid
concentrati~ns can also cause changes in the analyte transport efficiency.
~utrix ~flects Originating in the ~las~u. The number of ions generated
in the ICP per part per billion in the sample can also vary, depending on the con-
centration of efficiently ionized elements in the sample. Most elements are effi-
ciently ionized in the ICP, so high concen~ations of most elements in the sample
cause a decrease in the number of analyte ions produced in the ICP [ 160,17 1,1721.
The total dissolved solid concentration for solutions to be analyzed by ICP-MS is
generally kept below 0.2%. Typically the ~atrix-depende~t change in
of ions generated in the ICP is less severe than about a 30% decreas
the severity of the ma~~-dependent change in signal depends critical
experimental variables including plasma power, nebulizer gas flow rate, and
itself,
sampling depth. For matrix effects that originate in the plasma there is little
if any dependence on the analyte or conco~tant element mass [173], in contrast to
changes in the transmission efficiency ions from the plasma to the
of
M
in the
~~trix-Ind~ce~ C~anges ~runs~iss~on Ions from the In~~ctivel~
of
p
~ ~ ~ ~lasma to ethe ss Spe~tro~eter ~etecto~ The most severe chemi~al
~
l
matrix efTects in IC~-MS are due to changes in the transmission efficiency of ions