Page 305 - Inorganic Mass Spectrometry - Fundamentals and Applications

292 alli id ay et al.

with which the data could be acquired was remarkable. The same team then went
on to de~onstrate that they could also determine Pb isotopic compositions at high
precision in situ with a laser (Walder et al., 1993~).
Although this instrument was originally marketed in terms the ease of ac-
of
quisition with which it could provide isotopic compositions of elements that were
already being studied with TIMS and secondary ionization mass spectrometry
(SMS), it quickly became apparent that it was capable of measuring the isotopic
compositions of elements that had hitherto proved intractable, as well as provid-
ing a new way of measuring in situ unprecedented precision (Christensen et al.,
at
1995; Halliday et al., 1995, 1997; Lee and Halliday, 1995a; Yi et al., 1995). Thus
this field unquestionably represents the most radical bre~through in high-preci-
sion isotope ratio inorganic mass spectrometry in recent years.
In these first 5 years, scientists have used multiple-collector inductively cou-
pled plasma mass spectrometry (MC-ICP-MS) achieve unprecedented precision
to
in the measurement of Cu, Zn, Ga, Cd, In, Sn, Te, HE, W, TI, Pb, Th, and U iso-
topic compositions at high sensitivity; made the first high-precision isotope dilu-
tion measurements of the earth's inventory of many poorly understood elements
such as In, Cd, Te, and the platinum group elements; determined the age of the
earth's core, the moon, and Mars using a new short-lived chronometer 182Hf-182W,
made the first precise Sr, Hf, W, and Pb isotopic measurements in situ; developed
a totally new class of high-precision stable isotope measurements the small, but
of
important fractionations of Zn and Cu in nature; and determined high-resolution
Pb isotope stratigraphies for portions of the world oceans. Clearly, this is but the
beginning; MC-ICP-MS offers exciting times ahead in fields well beyond the
bounds of isotope and trace element geochemis~.
of
This chapter first presents a review the rapidly developing range of MC-
ICP-MS ins~mentation available, then briefly surveys the initial experiments and
the
associated methodologies that have helped to characterize current and predicted
performance of this kind of mass spectrometer, and concludes with a description
of the exciting research areas, previously considered intractable, that are now
be
to
developing in the earth sciences, cosmochemistry, oceanography, and the life sci-
ences as a direct consequence of this technique.

In order to achieve isotopic ratio measurements that are of comparable precision
to those acquired by TMS, but using an ICP source, four difficulties have to be
overcome. First, the ICP source is maintained at a high pressure, primarily gener-
ated by the Ar used as the plasma support gas, in a similar manner to that com-
monly deployed in conventional ICP-MS (hereafter referred simply as ICP-MS).
to