Page 131 - Inorganic Mass Spectrometry - Fundamentals and Applications

Inductively Coupled Plasma Mass Spectrometry 121

1.0 - Na

0.8 - cu
c:
a, 0.6 - CS
U>
0.4 -
Ti
0.2 -

0.0' ~ " " " ' ~ ' i ' " ' ' " ~ ' ' l
0 200 400 600 800 1000
Matrix Concentration (ppm)
Matrix effects on 138Ba+ ICP-MS signal as a function of matrix element
concentration. Lens voltage was fixed.

~atrix-matched standards or standard additions can be used to prevent
analysis errors when chemical matrix effects due to space-ch~ge-induced ion
transmission changes are significant. However, these approaches do not prevent
analysis errors if there is significant drift due to orifice plugging or lens coating.
Flow injection approaches rnay be useful to reduce the rate of orifice plugging or
lens coating as a function of time. If dilution is impractical because of sensitivity
loss, it rnay be necessary to separate the analytes of interest from the sample
matrix.
to
Some researchers have reported instrumental modifications reduce chem-
ical matrix effects, including a three-aperture interface
[ 103,18 11 and removal of
the ion optics [ 1821. These modifications appear to reduce the total ion current,
and therefore, space-charge effects, before ions enter the quadrupole mass spec-
trometer. Modification of ion optic lens voltages and confi~urations may also
reduce space-charge-induced chemical matrix effects [ 183- 1861.
There have also been reports of reduced matrix-induced suppression of
is
analyte sensitivity when nitrogen added to the plasma [ 187, l SS]. However, only
high matrix concentrations of K and Na, both relatively light elements, were
investigated.
omp pen sating for ~he~ical ~atrix Eflects Using Inte~nal Standards or
Isotope ~ilutio~. If the analyte and internal standard signals are affected sim-
ilarly by the sample matrix, internal standardization can effectively compensate
for changes in sensitivity. For analytes that are efficiently ionized in the TC
matri~-induced change in sensitivity depends on analyte mass [1'74]. Therefore,
the internal standard must have a similar mass to the analyte ion [ 189,1901.