A novel method for measuring ultra-trace levels of U and Th in Au, Pt, Ir, and W matrices using ICP-QQQ-MS employing an O reaction gas
Increased demand for improving ultra-low background detection capabilities for rare-event fundamental physics applications has resulted in the need for fast, convenient and clean assay methodologies that either preclude or reduce chemical sample pre-processing. A novel method for the measurement of...
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Published in | Journal of analytical atomic spectrometry Vol. 35; no. 12; pp. 2859 - 2866 |
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Main Authors | , , |
Format | Journal Article |
Published |
08.12.2020
|
Online Access | Get full text |
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Summary: | Increased demand for improving ultra-low background detection capabilities for rare-event fundamental physics applications has resulted in the need for fast, convenient and clean assay methodologies that either preclude or reduce chemical sample pre-processing. A novel method for the measurement of ultra-trace concentrations (fg g
−1
level) of natural
232
Th and
238
U and non-natural tracer isotopes
229
Th and
233
U was demonstrated in a solution of 10 μg g
−1
each of Au, Pt, Ir, and W in 2% HNO
3
using an ICP-QQQ-MS. Polyatomic interference across an
m
/
z
range of 227-239 was characterized: the major interferent with
229
Th
+
is
194
Pt
35
Cl
+
; interferents with
232
Th
+
are
184
W
16
O
3
+
,
183
W
16
O
3
H
+
,
192
Pt
40
Ar
+
,
196
Pt
36
Ar
+
,
195
Pt
37
Cl
+
, and
197
Au
35
Cl
+
; those with
233
U
+
are
193
Ir
40
Ar
+
,
197
Au
36
Ar
+
, and
184
W
16
O
3
H
+
; and that with
238
U
+
is
198
Pt
40
Ar
+
. Scanning the selected
m
/
z
range of 227-270 showed that higher oxide polyatomic species from the matrix elements either did not form or did not create a significant background on the target analyte masses. All measured concentrations in standard solutions matched the target values within the 98% confidence interval. The Th measurements were 80% accurate or better at the 10 fg g
−1
level and above, and the U measurements were 90% accurate or better at the 10 fg g
−1
level and above. Measurements at the 1 fg g
−1
level were consistent with target values within 1 standard deviation, although the standard deviations of all three replicates were greater than 20% of the measured concentration value. Method detection limits in the matrix solutions were calculated to be 2.74 fg Th and 12.9 fg U. In an electronic sample, which typically has 0.1% precious metal content, our method would give detection limits of 274 fg Th and 1291 fg U given a maximum of 10 μg g
−1
coinage metal matrix. This method is but one example of how state-of-the-art quadrupole mass spectrometry and collision reaction cell technology can be leveraged to develop novel analytical capability at ultra-trace levels.
A mass shift method using ICP-MS/MS with O
2
reaction gas is used for ultra-trace determinations of U and Th in samples containing W, Ir, Pt, and Au derived polyatomic interferants without the need for extensive chemical sample preprocessing. |
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ISSN: | 0267-9477 1364-5544 |
DOI: | 10.1039/d0ja00220h |