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(
c
) The order of analysis should be calibration standards, followed by rinse, blank check (PB run
as a sample), check standard, control sample, sample, sample duplicate (up to 10 samples), and
finally a repeated check standard.
G. Calculations
Sample concentrations in ng/g are automatically calculated by the software using a
nonweighted least-squares linear regression calibration analysis to produce a best-fit line:
Y
= a
x
+ blank
Note that for the Agilent software used in this work, the sample blank is identical to the Cal Blk
and is essentially zero because high purity reagents are used.
The analyte concentration in the sample was then calculated:
where
x
= analyte concentration (ng/g);
y
= analyte to ISTD intensity ratio, which is the
measured count of each analyte’s standard solution data point in the calibration curve divided
by the counts of the ISTD at the same level; similarly, the blank = analyte to ISTD intensity ratio,
which is the measured count of the blank standard solution data point in the calibration curve
divided by the counts of the ISTD at the same level as the blank standard solution;
a
= slope of
the calibration curve (mL/ng); and DF = volume of the sample solution (mL) divided by sample
weight (g).
H. Method Validation
This method has undergone a thorough SLV using AOAC guidelines to probe its linearity, LOQ,
specificity, precision, accuracy, and ruggedness/robustness. Accuracy has also been affirmed by
comparison to ICP-atomic emission spectrometry (AES) results generated in the authors’ own
laboratory. In addition, reproducibility was estimated during a limited multilaboratory testing
(MLT) study employing six laboratories and four different ICP/MS instruments. Both the SLV and
MLT results are summarized in a concurrent publication.
References:
J. AOAC Int
. (future issue)
AOAC SMPR 2011.009
J. AOAC Int
.
95
, 297(2012)
DOI: 10.5740/jaoac.int.11-0441
AOAC SMPR 2014.004
J. AOAC Int
.
98
, 1042(2015)
Posted: October 1, 2015
Candidates for 2016 Method of the Year
72