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P
oitevin
:
J
ournal of
AOAC I
nternational
V
ol
.
95, N
o
. 1, 2012
177
Determination of Calcium, Copper, Iron, Magnesium,
Manganese, Potassium, Phosphorus, Sodium, and Zinc
in Fortified Food Products by Microwave Digestion and
Inductively Coupled Plasma-Optical Emission Spectrometry:
Single-Laboratory Validation and Ring Trial
E
ric
P
oitevin
Nestlé Research Center, QS Department Mineral Laboratory, Lausanne, Switzerland
Submitted for publication September 2011.
The recommendation was approved by the Methods-Centric
Committee on Nutritional Elements in Food as First Action.
See
“Methods News,” (2011)
Inside Laboratory Management
, September/
October issue.
Corresponding author’s e-mail:
eric.poitevin@rdls.nestle.comDOI: 10.5740/jaoacint.CS2011_14
FOOD COMPOSITION AND ADDITIVES
A single-laboratory validation (SLV) and a ring trial
(RT) were undertaken to determine nine nutritional
elements in food products by inductively coupled
plasma-optical emission spectrometry in order to
modernize AOAC
Official Method
SM
984.27. The
improvements involved extension of the scope
to all food matrixes (including infant formula),
optimized microwave digestion, selected analytical
lines, internal standardization, and ion buffering.
Simultaneous determination of nine elements
(calcium, copper, iron, potassium, magnesium,
manganese, sodium, phosphorus, and zinc) was
made in food products. Sample digestion was
performed through wet digestion of food samples
by microwave technology with either closed- or
open-vessel systems. Validation was performed to
characterize the method for selectivity, sensitivity,
linearity, accuracy, precision, recovery, ruggedness,
and uncertainty. The robustness and efficiency of this
method was proven through a successful RT using
experienced independent food industry laboratories.
Performance characteristics are reported for 13
certified and in-house reference materials, populating
the AOAC triangle food sectors, which fulfilled
AOAC criteria and recommendations for accuracy
(trueness, recovery, and
z
-scores) and precision
(repeatability and reproducibility RSD, and HorRat
values) regarding SLVs and RTs. This multielemental
method is cost-efficient, time-saving, accurate, and fit-
for-purpose according to ISO 17025 Norm and AOAC
acceptability criteria, and is proposed as an extended
updated version of AOAC
Official Method
SM
984.27
for fortified food products, including infant formula.
I
mprovement of AOAC
Official Method
SM
984.27
for
the determination of nine nutritional elements in food
products by inductively coupled plasma-optical emission
spectrometry (ICP-OES) after microwave digestion is one of
the priority methods identified as part of an AOAC pilot project
to validate approximately 10 prospective methods deemed most
urgently needed. Food-testing and nutrition laboratories need
robust and efficient methods with well-characterized reference
materials to facilitate compliance for minerals with nutritional
labeling laws and claim requirements, provide traceability for
food exports needed for acceptance in many foreign markets,
and improve the accuracy of nutrition information that is
provided to assist consumers in making sound dietary choices.
ICP-OES is one of the most commonly used techniques
within the food industry for accurate and cost-efficient routine
analyses of nutritional minerals in food products, plants, pet
food, raw materials, and feeding stuffs. This report describes
a multielemental and simultaneous determination of nine
major elements (calcium, copper, iron, potassium, magnesium,
manganese, phosphorus, sodium, and zinc) in food products
by ICP-OES after microwave digestion. Analytical procedure
of validation of this extended and updated version of AOAC
Method
984.27
was performed in accordance with ISO 17025
and AOAC guidelines.
The main differences compared to AOAC Method
984.27
method concern (
1
) the use of microwave digestion systems
(MDS) with open and closed vessels, and a single acid (nitric
acid) for an optimized sample preparation in order to strengthen,
improve element recoveries from difficult matrixes, and increase
sample throughput, favoring safety precautions and time-saving
for laboratory analysts; (
2
) the use of appropriate analytical
wavelengths for each element of interest and of an automatically
addedmix solution of appropriate internal standards and ionization
buffer in order to correct for physical and chemical interferences,
compensate for matrix effects induced by the complexity of the
food samples, improve short-term accuracy (repeatability) and
long-term stability (reproducibility and calibration curve validity
in a long analysis batch); and (
3
) the extension of application to
food matrixes, including infant formula covering all nine AOAC
food triangle sectors.
Procedure of method validation was performed through three
independent studies on food-grade salts, and in-house reference
and certified food materials.
Single-laboratory validation (SLV).
—With eight food-grade
salts and 10 in-house and certified reference materials using
ICP-OES equipment after a closed-vessel microwave-based
optimized digestion with a Mars Xpress system (CEM Corp.,
Matthews, NC).
2011.14 (MTE-01) MLT
FOR ERP USE ONLY
DO NOT DISTRIBUTE