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1720 Thompson et al.: Journal of AOAC I nternational Vol. 98, No. 6, 2015
7500cx from the SLV, a few Agilent 7700x, a PerkinElmer
ELAN DRC-e, and a Thermo X Series 2. On the other hand, it
is of interest to note the excellent RSDs for Mn and Cu across
these laboratories—likely due to the excellent sensitivity of
the ICP/MS for these elements and the effectiveness of the
CRCs in removing background interferences at somewhat
higher mass.
The accuracy of the present method can be further attested
to by comparison to an independent method, the commonly
used ICP-AES, also with microwave digestion. A full SLV was
performed on the SPIFAN matrix set in the authors’ laboratory
using the same microwave oven (CEM MARS 5 with
MARSXpress™ vessels) and two PerkinElmer Optima ICP
instruments. The mean 6-day ICP-AES results were compared
to the mean values from the ICP/MS MLT (similar to those
means in Table 4). The results are shown in Table 8. Again,
we must disregard the numbers for the Adult RTFs because the
ICP-AES data were acquired several months ahead of the MLT
study, and these products had probably physically deteriorated.
The remaining powder products show remarkable agreement
between the two spectroscopies. In general, MS data are higher
than those produced by emission, but seldom is there more
than 6% difference.
Conclusions
The method, as is, meets all SMPRs except for the LOQ of
Fe, Mn, and Cu. There was also substantial evidence presented
to support the accuracy and reproducibility of this method
through comparison to an independent method and through
analyses completed at independent laboratories with different
models of ICP/MS instruments. The data from the SLV and
MLT studies were consistent with each other. Additional
linearity work, spiking at low-levels, increasing sample size,
and/or additional low level standards would be needed to
prove accuracy at the lowest levels for Fe, Cu, and Mn.
Acknowledgments
We thank Andre Szabo for participating as the second
analyst in this SLV. Also, we thank the participants of the
OMA 2011.19 collaborative study that contributed nine-
element data for this report: Fan Xiang, Sudhakar Yadlapalli,
Isabelle Malaviole, Ashutosh Mittal, Michael Gray, Diana
Mould, and Michael Farrow.
References
(1) Official Methods of Analysis (2011) AOAC INTERNATIONAL,
Rockville, MD, SMPR 2011.009.
(2) Official Methods of Analysis (2014) AOAC INTERNATIONAL,
Rockville, MD, SMPR 2014.004
(3) Official Methods of Analysis (2011) AOAC INTERNATIONAL,
Rockville, MD, Official Method 2011.19.
(4) Pacquette, L., Szabo, A., & Thompson, J
(5) Official Methods of Analysis (2012) AOAC INTERNATIONAL,
Rockville, MD, Appendix L.
(6) Thompson, J., Pacquette, L., & Brunelle, S. (2015) J. AOAC Int.
98, in press
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