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Thompson et al.
: J
ournal of
AOAC I
nternational
V
ol.
98, N
o.
6, 2015
1711
Submitted for publication June 1, 2015.
This method was approved by the Expert Review Panel for Infant
Formula and Adult Nutritionals as First Action.
The Expert Review Panel for Infant Formula and Adult Nutritionals
invites method users to provide feedback on the First Action methods.
Feedback from method users will help verify that the methods are
fit-for-purpose and are critical for gaining global recognition and
acceptance of the methods. Comments can be sent directly to the
corresponding author or
methodfeedback@aoac.org.1
Corresponding author’s e-mail:
joseph.thompson@abbott.comDOI: 10.5740/jaoacint.15-142
Determination of Minerals and Trace Elements in Infant
Formula and Adult/Pediatric Nutritional Formula by
Inductively Coupled Plasma/Mass Spectrometry—A
Performance Evaluation: Single-Laboratory Validation, First
Action 2015.06
Joseph J. Thompson and Lawrence Pacquette
Abbott Nutrition, 3300 Stelzer Rd, Columbus, OH 43219
Sharon L. Brunelle
Brunelle Biotech Consulting, 14104 194th Ave NE, Woodinville, WA 98077
A method for determination of 12 minerals and
trace elements (Na, Mg, P, K, Ca, Cr, Mn, Fe,
Cu, Zn, Se, and Mo) in infant formula and adult/
pediatric nutritional formula was developed and
evaluated in a single-laboratory validation. Some
additional reproducibility data were obtained from
a small interlaboratory study. The method involves
microwave digestion of the sample followed by
inductively coupled plasma/MS and uses Ge and Te
as internal standards. The method is an extension
of
Official Method
SM
2011.19 and was compared to
AOAC
Standard Method Performance Requirements
(SMPRs
®
) 2011.009 and 2014.004 developed by the
AOAC Stakeholder Panel on Infant Formula and
Adult Nutritionals (SPIFAN). Repeatability precision
for the 12 elements in 11 SPIFAN matrixes and
National Institute of Standards and Technology
Standard Reference Material (SRM) 1849a was
<5%, meeting the SMPR criterion for repeatability.
Intermediate reproducibility (8 days, two analysts,
two instruments) in the 11 SPIFAN matrixes was
<5% for nine (Na, Mg, P, K, Mn, Fe, Cu, Zn, Se)
of the 12 elements in all 11 matrixes. The mean
reproducibility across 6–7 laboratories and seven
SPIFAN matrixes ranged from 2.5% for Cu to 7.1%
for P. Recovery from spiked matrixes varied from
90.1 to 109%, and accuracy of determination using
SRM 1849a ranged from 96.2 to 107.7%, meeting the
requirement of 90–110% recovery/accuracy.
I
n response to a need for reference methods for dispute
resolution, the AOAC Stakeholder Panel on Infant Formula
and Adult Nutritionals (SPIFAN) developed
Standard
Method Performance Requirements
(SMPRs
®
) for
Official
Methods of Analysis
for the ultratrace elements Cr, Mo, and Se
(AOAC SMPR 2011.009; 1) and for the major/trace elements
Ca, Mg, P, K, Na, Cu, Fe, Mn, and Zn (AOAC SMPR 2014.004;
2) in infant formula and adult/pediatric nutritional formula.
AOAC
Official Method
SM
2011.19
(3) for determination of Cr,
Mo, and Se, previously validated and shown to conform to the
requirements of SMPR 2011.009, was expanded to include the
minerals and trace elements contained in SMPR 2014.004. The
method includes addition of internal standards (ISTDs) prior
to microwave digestion of the sample in the presence of nitric
acid and hydrogen peroxide. The diluted digestate is analyzed
by inductively coupled plasma (ICP)/MS, and response ratios
of analyte:ISTD in unknown samples are compared to external
calibration curves to generate a result for each analyte.
AOAC SMPR 2011.009 (1) provides the performance
criteria for Cr, Mo, and Se, and SMPR 2014.004 (2) provides
the performance criteria for Ca, Cu, Fe, Mg, Mn, P, K, Na, and
Zn. The criteria are summarized in Table 1. This manuscript
reports the results of the single-laboratory validation (SLV)
and some limited reproducibility data for the ICP/MS method
for 12 minerals and trace elements and comparison to the
acceptance criteria. Based on the data presented, the AOAC
Expert Review Panel on SPIFAN Nutrient Methods granted the
method First Action status for the nine elements in March 2015.
Note that similar data for just Cr, Mo, and Se were presented
in a prior publication (4), but that SLV was conducted on a
different set of matrixes.
The SLV was conducted in accordance with the guidelines
recommended by SPIFAN (5) and included determinations of
specificity, linearity, LOQ, repeatability precision, and recovery/
accuracy in 11 matrixes identified by SPIFAN. The matrixes
cover a variety of nutritional formulations, including powders
and ready-to-feed (RTF) liquids made from milk, soy, whey,
hydrolyzed protein, and amino acids, with and without intact
protein. This SLV was performed by two analysts using two
Agilent (Santa Clara, CA) ICP/MS instruments, one a 7500cx
and the other a 7700x. The microwave oven was a CEM Corp.
(Matthews, NC) MARS 5 with MARSXpress™ vessels.
INFANT FORMULA AND ADULT NUTRITIONALS
70