Page 288 - Inorganic Mass Spectrometry - Fundamentals and Applications

2 74 ~ar~us

ing and mixing are not part of the protocol, analysis speed, greater temporal sta-
bility, and retention of spatial infomation are key advantages. The applications
of
highlighted here demonstrate these attributes and also provide a glimpse a much
higher level of analytical versatility than the sample compaction method, In addi-
tion to the glass and metal oxide samples described in the previous discussions,
certain oxide and carbide materials have physical properties that simply prohibit
mechanical grinding procedures. This of course makes solution-based analysis a
less than attractive choice.
Glow discharge mass spectrometry is generally considered to be underuti-
lized with regard to its inherent capabilities for isotope ratio analysis of solid ma-
terials. In fact, studies have shown that the technique can be applied to produce
meaningful analytical precision and accuracy. The group of Betti and coworkers
E251 has been a leader in GD-MS analysis of nuclear materials. In those instances
in which nonconductive powders require analysis, direct compaction (i.e., without
binder) with analysis through the use of a secondary cathode has shown to be an
effective alternative to standard thermal ionization mass spectrometry (TIMS).
Comparisons between the two techniques were made for the elements Li, B, Si,
Zr, U, and Pu. Only in the case of Pu were the TIMS data appreciably better than
the GD-MS, whereas mathematical corrections for interference from U and Am
were required to produce comparable statistics to TIMS. The authors concluded
that CD-MS was very competitive with thermal ionization; the former was con-
sidered to be virtually nondestructive since only very small amount (nanograms)
of material are actually lost to the analysis, though the sample preparation required
to isolate those materials is very time consuming and complex.
The most creative application of the secondary cathode approach was de-
scribed by Schelles and Van Grieken [24], who investigated its ability to determine
the elemental constituents of polymeric materials. Mass spectrometric analysis has
almost exclusively been directed at the determination of molecular weights and
[53,54] and ma-
disparity characteristics; secondary ion mass spectrometry (SIMS)
trix assisted laser desorption ionization (MALDI) [55,56] have carried the major
share of the workload. Growing concerns over the fate of polymeric materials in
the environment and the leaching of heavy metals into ground waters have neces-
of
sitated the development of methods that permit the elemental analysis bulk poly-
mers. In addition, the use of polymers as i~obili~ation media for waste remedi-
ation is also pressing these developments.
Schelles and Van Crieken [24] used a Ta secondary cathode for the sputter-
ing of polytetrafluoroethylene (PTFE), polycarbonate (PC!), and polyvinylchloride
(PVC) sheets of 0.5- to 1.0-mm thickness. Very di~erent from in the case of sput-
tering metals or oxides, the thermal energy deposited during the course of sput-
tering can be catastrophic for polymers that are subject to melting or even pyroly-
sis. This in fact was the case for PC, which melted under conditions in which the
other two polymers operated stably. general, the authors felt that practical analy-
In
sis was only possible for polymers with melting points
>lOO°C. In the case of PTFE