Aa. Specht et D. Beauchemin, AUTOMATED ONLINE ISOTOPE-DILUTION ANALYSIS WITH ICP-MS USING SANDWICHFLOW-INJECTION, Analytical chemistry, 70(5), 1998, pp. 1036-1040
An automated flow injection (FI) manifold is described to perform the
addition of isotopic spikes to aqueous samples on-line with ICP-MS for
isotope dilution (ID) analysis. The manifold uses the sandwich techni
que (with the nested loop approach) to perform an injection of the iso
topic spike solution within a sample (or standard) plug, the resulting
sample-spike-sample sequence being pushed toward the nebulizer by a 1
% HNO3 carrier, A standard, which must contain one element not present
in the spike solution to allow the determination of the dispersion co
efficient, must also be used to allow a reverse isotope dilution analy
sis, as well as corrections for mass discrimination and/or spectroscop
ic interferences. Indeed, because the signals from the individual isot
opes are monitored continuously, only one isotope free of spectroscopi
c interference is required for elements whose isotopic distribution do
es not vary in nature (two isotopes are still needed for the other ele
ments), as a correction for the interference can be made by comparison
with the signals from the standard. Furthermore, this automated appro
ach makes ID-ICP-MS a faster method and does not require any prelimina
ry analysis of the sample because the concentration profile resulting
from EI allows the selection of the best isotopic ratio. It was succes
sfully applied to the determination of Mo in saline water.