Thevalidationof thismethod involveda single-laboratory
validation (SLV), a ruggedness study, anda ring trial (RT) in
accordancewith ISO17025 andAOACguidelines (26):
(
a
)
SLV
.—Performed using ICP-AES with axial grating
afteraclosed-vesselmicrowavedigestion,on10in-houseand
certified referencematerials.
(
b
)
Ruggedness study
.—Performed in parallel, analyzing
with and without ionization buffer, the spiking elements in
eight food-grade salts and testing six in-house and certified
reference materials in repeatability and reproducibility
conditions with different ICP-AES equipment (axial, radial,
and dual-view grating configurations) after open- and
closed-vesselmicrowave-baseddigestions.
(
c
)
RT.
—Involving nine laboratories was organized to
analyze five in-house and certified referencematerials.
Thirteen well-characterized reference materials were
selected topopulate theAOACtriangle, inwhich foods could
be categorized intonine sectors basedon their fat, protein, and
carbohxdrate contents (27). All the results obtained on
reference materials have been treated with robust
statistics (28, 29) to verify that the updated procedure is
fit-for-purpose in terms of specificity, sensitivity, linearity,
trueness, and precision; and can be proposed as an improved
versionofofficialAOACMethod
984.27
regardingmicrowave
digestion, internal standardization, and ionbuffering.
Experimental
Apparatus
(
a
)
Closed-vesselmicrowavedigestionsystems
.—ACEM
Mars Xpress (CEM, Matthews, NC) was used for the SLV,
including ruggedness test MD1 (Table 1). Other microwave
systems from CEM and Milestone (Shelton, CT) suppliers
wereused for ruggedness testsMD2,MD3, andMD4and for
the collaborative studyRT (Table 1).
(
b
)
Open-vessel microwave digestion system
.—A CEM
MDS2000was used for testMD2 and by one laboratory for
theRT.
(
c
)
ICP-AES spectrometers
.—A Varian Vista-Pro axial
ICP-AES instrument with SPS-5 autosampler (Varian Inc.,
Mulgrave, Victoria, Australia) was used for the SLV,
includingtestsMD1andMD2.Other ICP-AESspectrometers
from Perkin Elmer (Norwalk, CT), Varian, and Spectro
(Kleve,Germany)wereused for theMD3andMD4 tests and
for theRT.
(
d
)
Balance
.—A balance (AT 200, Mettler-Toledo, Inc.,
Greifensee,Switzerland)withreadabilityof0.1mg(SLV, tests
MD1andMD2) or equivalent (testsMD3,MD4, andRT).
(
e
)
Sub-boilingquartz distillationapparatus for acids
.—A
Kürner Analysentechnik (Rosenheim, Germany) distillator
(SLV,MD1, andMD2) for purifyingacidsor equivalent (tests
MD3,MD4, andRT).
(
f
)
Fumehood
.—A fumehood acid-resistant was used
(SLV, testsMD1 andMD2) or equivalent (testsMD3,MD4,
andRT).
(
g
)
Drying oven
.—A Heraeus drying oven 6120T
(Heraeus, Hanau, Germany) was used for the SLV, and tests
MD1 and MD2, and similar equipment was used for tests
MD3,MD4, andRT.
(
h
)
Mixer or grinder for homogenization
.—A Retsch
(Haan, Germany)mixer GM200was used for the SLV, tests
MD1 andMD2, or equivalent (testsMD3,MD4, andRT).
P
OITEVINETAL.
: J
OURNALOF
AOACI
NTERNATIONAL
V
OL
. 92,N
O
. 5, 2009
1485
Table 1. Microwavedigestionsystems (MD1,MD2,MD3,MD4) and ICP-AESequipment used for single-laboratory
validationand ring trial
Test code
a
Digestionmode
b
Digestionequipment
Nebulizer/chamber
ICPequipment
Gratingconfiguration
SLV
MDC
CEMMarsXpress Concentric/cyclonic
VarianVistaProAX
Axial view
MD1
MDC
CEMMarsXpress Concentric/cyclonic
VarianVistaProAX
Axial view
MD2
MDO
CEMMDS2000 Concentric/cyclonic
VarianVistaProAX
Axial view
MD3
MDC
MilestoneMLSEthos Concentric/cyclonic
SpectroCiros
Radial view
MD4
MDC
MilestoneMLS1200 Concentric/cyclonic PerkinElmerOptima5300DV
Dual view
RT
MDC
CEMMarsXpress Concentric/cyclonic PerkinElmerOptima5300DV
Dual view
RT
MDC
CEMMars5
Concentric/cyclonic PerkinElmerOptima2000DV
Dual view
RT
MDC
CEMMarsXpress Concentric/cyclonic
Varian720ES
Axial view
RT
MDC
CEMMarsXpress
Crossflow/scott
PerkinElmerOptima3300RL
Radial view
RT
MDO
CEMMDS2000
Crossflow/scott
PerkinElmerOptima4300DV
Dual view
RT
MDC
CEMMarsXpress Concentric/cyclonic
Varian720ES
Axial view
RT
MDC
CEMMarsXpress Concentric/cyclonic PerkinElmerOptima2100DV
Dual view
RT
MDC
CEMMarsXpress Concentric/cyclonic PerkinElmerOptima5300DV
Dual view
RT
MDC
CEMMarsXpress Concentric/cyclonic PerkinElmerOptima2100DV
Dual view
a
SLV=Single-laboratoryvalidation;MD= ruggedness test usingdifferentmicrowavedigestionsystemsand ICP-AESequipment; RT= ring
trial.
b
MDC=Closed-vesselmicrowavedigestionsystem;MDO=open-vesselmicrowavedigestionsystem.
MTE-01
FORWORKINGGROUP/ERPUSEONLY
DONOTDISTRIBUTE
