(
g
)
Digestion vessel decontamination for open-vessel
microwave digestion (MD2 ruggedness test)
.—The glass
volumetric flasks canbedirectlyusedafter beingwashed ina
laboratory washing machine or soaked overnight in a water
bathwithHNO
3
30%(v/v) and rinsedwithH
2
O to avoid or
minimize riskof iron contamination.
(
h
)
Spiked food grade salt preparation (SLV)
.—Weigh
0.2 ± 0.01 g food-grade salt into a 100mLvolumetric flask.
Add deionized water and 10 mLHNO
3
. Add 0.8 mL stock
standard solution corresponding to standard Std4 [prepared
fromCPI commercial solution (Ca, 60mg/L; Cu, 0.4mg/L;
Fe, 2mg/L; K, 80mg/L;Mg, 20mg/L;Mn, 0.01mg/L; Na,
40mg/L; P, 40mg/L;Zn, 0.8mg/L)].Dissolve salt anddilute
tovolumewithdeionizedwater.
ICPAnalysis
(
a
)
ICP-AES spectrometer (SLV-MD1 and MD2
ruggedness tests)
.—A Varian Vista-Pro axial ICP-AES
instrumentwithautosamplerSP5wasusedduringSLV,using
theoperatingconditionsshown inTable4.Therecommended
and alternative analytical lines (nm) used for elements to be
determined and internal standards (IS) are shown inTable 5.
A3-channelperistalticpump(Gilson,Middleton,WI)andaT
connector (id 1.5 mm/Socochim, Lausanne, Switzerland)
linked between the peristaltic pump and nebulizer were used
to avoid having tomanually add ionization buffer and IS to
each sample solution. A thermostatted (15 C) cyclonic spray
chamber (Jacketed ‘Althea’ CyclonicGlass SprayChamber,
water-cooled, EPOND SA, Vevey, Switzerland) equipped
withamicro-concentricnebulizer [C-Type ‘Caliber’ standard
ConcentricGlassNebulizerwith ‘NebLink’ sample capillary
tube and argon connector (EPOND)]were used to obtain the
best method performance. Sample and IS pump tubes (e.g.,
orange/white, 0.64 mm id Socochim), and peristaltic pump
rotation speed (15 rpm), were selected tokeep sample and IS
pump tubes of similar size to maximize mixing accuracy,
while maintaining the required detection levels. Ionization
buffer (cesium chloride) was combined with IS solution to
compensate for easy ionizable element (EIE) effects (e.g., K,
Na, andCa) in theplasma, becausecertain foodmaterials can
contain substantial concentrations of these elements that
provide a significant source of electrons in the plasma. The
presenceof ionizationbuffer inall samplesandstandardswill
minimize the effects of varying concentrations of EIEs in the
P
OITEVINETAL.
: J
OURNALOF
AOACI
NTERNATIONAL
V
OL
. 92,N
O
. 5, 2009
1489
Table 6. RecoveryandSDvalues found for nineelementsusing recommended linesafter optimizationofCEMMars
Xpressmicrowavedigestionof twoStandardReferenceMaterials (NISTSRM2384, NISTSRM2383) andone
ReferenceMaterial (NISTRM8415)
Concentration,mg/kg
Element
Bakingchocolate
(NISTSRM2384)
Wholeeggpowder
(NISTRM8415)
Baby foodcomposite
(NISTSRM2383)
Calcium
Certified
a
840±74
2480±190
853±28
Found
b
(recovery,%)
c
793±100 (94)
2627±358 (106)
868±12 (102)
Copper
Certified
a
23.2±1.2
2.70±0.35
1.42±0.12
Found
b
(recovery,%)
c
24.1±0.2 (104)
2.90±0.05 (107)
1.77±0.22 (125)
Iron
Certified
a
132.0±1.1
112±16
8.44±0.44
Found
b
(recovery,%)
c
129.6±1.2 (98)
105±0.3 (94)
10.41±1.11 (123)
Potassium
Certified
a
8200±500
3190±370
3600±100
Found
b
(recovery,%)
c
7750±100 (95)
3125±27 (98)
3793±33 (105)
Magnesium
Certified
a
2570±150
305±27
248±5
Found
b
(recovery,%)
c
2567±34 (100)
292±1 (96)
245±3 (99)
Manganese
Certified
a
20.3±1.3
1.78±0.38
1.39±0.11
Found
b
(recovery,%)
c
19.9±0.1 (98)
1.62±0.01 (91)
1.42±0.002 (102)
Sodium
Certified
a
40±4
3770±340
390±28
Found
b
(recovery,%)
c
ND
d
3550±222 (94)
378±7 (97)
Phosphorus
Certified
a
3330±210
10010±320
948±33
Found
b
(recovery,%)
c
3301±48 (99)
11643±295 (116)
962±10 (101)
Zinc
Certified
a
36.6±1.7
67.5±7.6
10.5±0.3
Found
b
(recovery,%)
c
35±0.5 (96)
60.9±0.1 (90)
10.6±0.03 (101)
a
Uncertaintyexpressedeither asa95%confidence interval or asan interval basedon theentire rangeof accepted results for asingle
determination.
b
SD fromaverageof triplicatesanalysis.
c
Foundvalue/certifiedvalue ratioexpressed in%.
d
ND=Not determined (<LOQ).
MTE-01
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