Posting type

Advisory

Subject

Module/Species

Sites

Period

Recommendation
Submitter

Calibration bias in reported Vanadium concentration
Teflon 47 mm
Entire network

CSN samples Nov 2015- Oct 2017
Divide reported concentrations by 1.3
K.Trzepla, ktrzepla@ucdavis.edu

Supporting information

Elemental concentrations from XRF analysis are based on linear calibrations of the
instruments. Two thin-film standards certified by a commercial manufacturer have
underpinned the V calibration. After comparisons with other laboratories and other reference
materials showed discrepancies in results for V, these standards were returned in 2017 to the
original manufacturer for recertification. The recertified loadings reported in 2017 were lower
than previously certified values by a factor of about 1/1.3.

The XRF systems have been recalibrated using the newly certified V loadings of the same two
original standards. The updated calibration yields XRF values consistent with quoted loadings
for four new V standards purchased from the same manufacturer in 2017. These cover a range
of lower mass loadings, as shown in Figure 1.

V concentrations in samples collected starting in November 2017 are being reported with the
new XRF calibration. Retrospective application of the 2017 recalibration back to 2016 assumes
that the standards themselves did not change between their 2016 and 2017 certifications, and
annual calibration records provide evidence of this stability (Fig.2).

Vanadium standards from manufacturer

• 2011 (Original Certified Values) O 2011 (Re-certified) ~Jul2017 (new standards)

1.4

1.3

"O

CD

£ 1.2

0)

U

£ ii
x

0.9

1.6

£ 1.4
o

z12

tt

£ 1.0
re

£ 0.8
o

*0.6
<

„E 0.4

i/i

8- 0.2

0.0





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Fig. 1 Reported vs. quoted V mass
loadings for commercial thin-film
standards. The reported XRF values
are based on a calibration to the
loadings certified in 2017 for the two
standards originally purchased in 2011.

20	, 40

Certified, ng/cm2

Stability of Vanadium standards (2011 - 2017)

	—«-V 32518 —«-V 32517	

60

Fig. 2 Raw response of an XRF analyzer
to two specific calibration standards
used throughout 2011 - 2017,
normalized to Fe to account for
physical changes in the system. The
results show no evidence of changes in
the standards during this period.

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