Page 277 - Inorganic Mass Spectrometry - Fundamentals and Applications

Sample Types
Analysis of ~oncon~uctive 263

scribes the analysis of insulating materials by GD-MS, a review by Winchester et
al. provides additional background for such analyses for the complete family of
GD spectroscopies [36]. It is hoped that the reader will see that there are indeed a
number of options available for meeting the challenges presented by this ever-in-
creasing and important set of sample types.

The use of the sample compaction methodology is an effective means ofanalyz-
ing powder-form samples such as geological materials and spent automotive cat-
alysts. The mixing of powders with conductive host metals involves four basic
steps: (1) drying of the sample to drive off residual water, (2) weighing appropri-
ate amounts of sample and binder, (3) mixing mechanically to homogenize the
components, and (4) pressing the sample into the appropriate size and shape as dic-
a
tated by the sample holder. Each of these steps involves finite period and requires
judicious optimization and protocol development. The use of the sample com-
paction methodology was introduced early ('1972) in the evolution of glow dis-
et
charge atomic emission spectrometry by Dogan al. [ 181. Marcus and coworkers
reviewed a great deal of the developmental aspects of the compaction methodol-
ogy as it applies to GD-AES [36]. Loving and Harrison E371 published the first de-
scription of the use of the compaction procedure for mass spectrometry in 1983 as
part of a study evaluating the role of water vapor on GD-MS performance with a
for
dual-pin cathode geometry. Borrowing from the methodology developed spark
of 90% graphite and 10% ar-
source mass spectrometry, pin electrodes composed
senic powder were formed by using a die and hydraulic press. Stable [42% rela-
tive standard deviation (RSD)] As+ signals were produced, though the published
spectrum clearly displayed that residual water and atmospheric species were major
spectral components. Harrison and coworkers [38] revisited the approach in an
early investigation of a hollow cathode plume (HGP) ionization source, wherein
an alumina-based automotive catalyst was mixed 50:50 in a silver matrix. Neither
of these early studies delved into the determination of the most effective imple-
mentation of the compaction procedure, though they demonstrated characteristics
that have launched a series of detailed studies.

Throughout the literature describing the compacted sample methodology, the
to
choice of the binder material has time and again been pointed as the most im-
portant aspect in determining source performance. Papers by Tong and Harrison
[39], Mei and Harrison [40,41], Smith and coworkers [42,43], and Wayne [44] have