P
oitevin
:
J
ournalof
AOAC I
nternational
V
ol
.
95, N
o
. 1, 2012
177
DeterminationofCalcium,Copper, Iron,Magnesium,
Manganese, Potassium, Phosphorus, Sodium, andZinc
inFortifiedFoodProductsbyMicrowaveDigestionand
InductivelyCoupledPlasma-OpticalEmissionSpectrometry:
Single-LaboratoryValidationandRingTrial
E
ric
P
oitevin
NestléResearchCenter, QSDepartmentMineral Laboratory, Lausanne, Switzerland
Submitted for publicationSeptember 2011.
The recommendationwas approved by theMethods-Centric
Committee onNutritional Elements inFood as FirstAction.
See
“MethodsNews,” (2011)
InsideLaboratoryManagement
, September/
October issue.
Corresponding author’s e-mail:
DOI: 10.5740/jaoacint.CS2011_14
FOODCOMPOSITIONANDADDITIVES
Asingle-laboratoryvalidation (SLV) anda ring trial
(RT)wereundertaken todetermineninenutritional
elements in foodproductsby inductivelycoupled
plasma-optical emissionspectrometry inorder to
modernizeAOAC
OfficialMethod
SM
984.27. The
improvements involvedextensionof thescope
toall foodmatrixes (including infant formula),
optimizedmicrowavedigestion, selectedanalytical
lines, internal standardization, and ionbuffering.
Simultaneousdeterminationof nineelements
(calcium, copper, iron, potassium,magnesium,
manganese, sodium, phosphorus, and zinc)was
made in foodproducts. Sampledigestionwas
performed throughwet digestionof foodsamples
bymicrowave technologywitheither closed- or
open-vessel systems. Validationwasperformed to
characterize themethod for selectivity, sensitivity,
linearity, accuracy, precision, recovery, ruggedness,
anduncertainty. The robustnessandefficiencyof this
methodwasproven throughasuccessful RTusing
experienced independent food industry laboratories.
Performancecharacteristicsare reported for 13
certifiedand in-house referencematerials, populating
theAOAC triangle foodsectors,which fulfilled
AOACcriteriaand recommendations for accuracy
(trueness, recovery, and
z
-scores) andprecision
(repeatabilityand reproducibilityRSD, andHorRat
values) regardingSLVsandRTs. Thismultielemental
method iscost-efficient, time-saving, accurate, andfit-
for-purposeaccording to ISO17025NormandAOAC
acceptabilitycriteria, and isproposedasanextended
updatedversionofAOAC
OfficialMethod
SM
984.27
for fortified foodproducts, 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 prioritymethods identified as part of anAOACpilot project
tovalidate approximately10prospectivemethods deemedmost
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 inmaking 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
andAOAC 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 anoptimized sample preparation inorder to strengthen,
improve element recoveries fromdifficultmatrixes, 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 andof an automatically
addedmixsolutionofappropriateinternalstandardsandionization
buffer inorder tocorrect for physical andchemical 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
foodmatrixes, including infant formula covering all nineAOAC
food triangle sectors.
Procedureofmethodvalidationwas performed through three
independent studies on food-grade salts, and in-house reference
and certified foodmaterials.
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).
MTE-01
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