ARTICLE IN PRESS
Journal of Trace Elements in Medicine and Biology 21 (2007) S1, 10–13
www.elsevier.de/jtemb
THIRD INTERNATIONAL FESTEM SYMPOSIUM
Determination of iodine in human milk and infant formulas
Luisa Maria Fernández-Sáncheza,, Pilar Bermejo-Barreraa,
José Maria Fraga-Bermudezb, Joanna Szpunarc, Ryszard Lobinskic
a
Department of Analytical Chemistry, Nutrition and Bromatology, Faculty of Chemistry, 15782 Santiago de Compostela, Spain
Department of Pediatrics, Hospital Clinico Universitario, 15706 Santiago de Compostela, Spain
c
LCBAIE, UMR 5254 CNRS, Hélioparc, 2 Avenue Du Pr. Angot, 64053 Pau-Pyrénées, France
b
Received 10 June 2007; accepted 10 August 2007
Abstract
The aim of this study was to develop a method to determine iodine in human milk and infant formulas using
ICP-MS. The milk samples were digested using an alkaline digestion (5% NH3, 45 W, 2 min and 30 s), and the method
was validated using a certified reference material (CRM) BCR CRM151. On the other hand the milk was separated in
three fractions, whey, fat and caseins using ultracentrifugation (15 min, 4 1C, 50,000 rpm) and the iodine was
determined in the different fractions. About 27 samples of different infant formulas and 14 samples of human milk
have been studied. In the human milk the values found were between 144793.2 mg kg1, whereas in the infant formulas
the values were 53.3719.5. For both types of samples the bigger amount of iodine is in the whey fraction, between
80% and 90%, whereas in the fat there is about a 2% of the total iodine and in the casein fraction the levels are
between 5% and 10% depending on the type of sample.
r 2007 Elsevier GmbH. All rights reserved.
Keywords: Human milk; Infant formulas; Iodine; Alkaline digestion; ICP-MS
Introduction
Iodine is an essential micronutrient to animals and man.
It is a constituent of the thyroid hormones the lack of
which causes poor mental and physical development in
children and goiter in adults [1]. In early infancy, breast
milk and formulas are the only dietary source of essential
trace elements. The mother’s milk provides an adequate
supply of all micronutrients for the full-term infant. The
concentrations of the essential trace elements in human
milk are therefore used as in Ref. [2]. In infant nutrition the
iodine level in breast milk is known to be affected by the
maternal diet whereas infant formula needs to be
supplemented with iodine [3]. Since excessive intake of
Corresponding author.
E-mail address: [email protected] (L.M. Fernández-Sánchez).
0946-672X/$ - see front matter r 2007 Elsevier GmbH. All rights reserved.
doi:10.1016/j.jtemb.2007.09.006
iodine can cause toxic goiter (thyrotoxicosis) the supplementary iodine should be strictly limited and controlled by
manufacturers and government institutions [4].
Due to the low levels of iodine in milk it is necessary
to use an analytical technique with low detection limit,
for example the ICP-MS. Since problems were encountered during the direct determination of iodine in milk
by ICP-MS, the sample digestion it is necessary [5,6]. In
this paper a rapid open-vessel focussed microwave
assisted digestion was developed for this purpose.
Material and methods
Instrumentation
An ELAN 6000 ICP mass spectrometer (PE-SCIEX,
Thornhill, Ontario, Canada) was used as the element-
ARTICLE IN PRESS
L.M. Fernández-Sánchez et al. / Journal of Trace Elements in Medicine and Biology 21 (2007) S1, 10–13
specific detector. The sample was introduced into the
ICP via cross-flow nebulizer fitted in a Ryton spray
chamber. For quantification of iodine the samples were
fed by means of a Minipuls 3 peristaltic pump (Gilson,
Villiers-le-bel, France) that also served for draining the
spray chamber.
A Hitachi Model Himac CS 120GX refrigerated
ultracentrifuge (Jouan, Saint Herblain, France) was
used for the separation of the milk whey. The samples
were digested in a 22 mL open vessel of borosilicate glass
Table 1.
11
fitted with a 10 cm condenser using Synthewave S402
microwave digester (2.45 GHz, maximum power 300 W)
(Prolabo, Fontenay-sous-Bois, France).
Reagents, standards and samples
Analytical-grade reagents purchased from SigmaAldrich (St. Quentin Fallavier, France) were used
throughout unless specified otherwise. 18 MO Milli-Q
Total iodine in different infant formulas
[I] mg per 100 g infant formula
Whole milk
n¼3
Milk whey
n¼3
‘‘Nestlé’’
Nativa-1
Nidina-1
Nativa-1’
Nidina-1’
Nan-1
Nidal
46.572.8
41.574.0
43.572.1
66.978.9
57.673.5
47.473.3
18.572.5
40.273.4
37.874.3
61.975.7
34.672.6
24.475.1
2.570.9
4.171.1
2.971.2
12.472.5
5.371.9
3.171.2
1.570.9
2.371.1
1.270.7
2.270.9
6.771.8
3.572.1
‘‘Milupa’’
Aptamil
Milumil 1
50.073.7
48.872.9
20.074.2
25.975.1
1.970.6
8.771.1
6.472.1
7.371.7
‘‘Ordesa’’
Blemil Plus 1
Blevimat
51.273.6
54.275.8
30.073.4
52.772.6
5.271.8
2.170.9
4.172.1
1.870.5
‘‘Meed Johnson’’
Enfalac-1
Enfalac-1’
Enfamil
43.670.21
52.873.9
62.271.3
30.171.2
14.971.1
42.174.2
2.570.7
3.170.7
6.571.6
4.971.2
2.5071.1
5.171.2
‘‘Sandoz-Nutrición’’
Modar 1
Adapta 1
Damira
Modar digestión
33.071.2
36.173.2
21.174.1
54.972.1
22.172.1
16.171.7
15.172.1
49.871.6
2.170.4
3.270.6
1.270.3
2.770.4
1.770.2
4.370.9
1.170.8
2.370.7
53.871.6
109.875.0
101710.4
50.471.8
100.674.2
80.674.2
1.570.5
7.371.2
4.171.3
1.270.6
1.970.9
3.371.2
‘‘Nutricia’’
Almirón-1 A.R.
Almirón-1
Almirón PEPTI
Fat
n¼3
Casein
n¼3
‘‘Granja Castelló’’
Nadó
68.874.0
4872.5
15.770.6
3.871.0
‘‘Miltina’’
Miltina
35.672.2
24.172.5
2.571.1
1.670.9
‘‘Wyeth’’
S-26
Natal SMA-Nutribén
38.373.9
58.371.5
31.773.5
39.972.5
2.771.0
6.372.2
1.870.6
5.371.4
‘‘Similac Ross Products’’
Similac Ross Pediatric-1
Similac Ross Pediatric-1’
42.176.7
82.375.6
31.373.3
74.774.7
8.373.4
2.171.1
4.170.7
7.770.8
‘‘Hero’’
Hero baby
38.971.1
6.272.4
6.772.1
10.570.7
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12
Table 2.
L.M. Fernández-Sánchez et al. / Journal of Trace Elements in Medicine and Biology 21 (2007) S1, 10–13
Human milk from Santiago de Compostela (Galicia, Spain)
[I] mg kg1
Human milk
Whole milk
n¼3
Milk whey
n¼3
Fat
n¼3
Casein
n¼3
1
2
3
4
5
6
7
8
9
10
11
12
13
14
13272.1
17673.2
14073.5
11972.2
18271.8
9171.5
48.371.1
14372.4
43278.5
13173.5
10574.2
5772.8
22873.4
67.574.2
109.272.5
14273.4
135.474.4
9273.7
132.474.6
7972.4
44.572.3
134.273.7
283.574.6
11976.4
6973.1
5472.5
13174.7
50.373.5
5.671.8
27.171.6
11.272.5
9.972.7
11.872.8
3.873.1
1.270.9
7.572.5
71.676.8
8.572.4
12.173.4
4.1372.1
27.073.5
5.771.4
9.372.5
–
10.471.8
12.372.1
12.472.6
5.471.9
2.571.1
9.672.1
–
–
–
–
–
–
water (Millipore, Bedford, MA, USA) was used
throughout.
The potassium iodide was used as standard. A certified
reference material (CRM) 151 skim milk powder (BCR,
Brussels, Belgium) with a certified iodine concentration of
5.3570.14 mg g1 was used to control the accuracy of the
total iodine determination.
The human milk samples were collected from mothers
having delivered at the Hospital Clinico in Santiago,
Spain. The samples were collected in polypropylene
containers cleaned with 10% HNO3 and immediately
frozen (20 1C). Infant formula samples were purchased
in pharmacy.
Sample preparation
Infant formulas and the CRM powder were reconstituted with water according to manufacturer’s recommendations.
A sample aliquot was centrifuged at 50,000 rpm at
4 1C for 15 min, three fractions were obtained, fat, milk
whey and casein fraction [7].
Determination of total iodine by ICP-MS
For the analysis of total iodine, 2 mL aliquot of a milk
sample was placed in a reaction tube together with 5 mL
of 0.5% v/v ammonia solution and digested in the
focussed microwave system at 45 W for 2 min and 30 s.
The resulting solution was diluted to 10 mL and fed
directly into the ICP-MS [7].
The method of standard additions (10 and 20 mg L1)
was applied for the quantification of the iodine content.
Rh was used as the internal standard. The method
developed was validated by analysing the BCR CRM
151 skim milk powder. The mean of the results from
different days was 5.4370.06 mg g1 (n ¼ 5), in comparison with the certified value of 5.3570.14 mg g1
(n ¼ 5). The precision of five measurements realised
during the same day was 3–4%. The limit of detection
was 0.27 mg L1 and the limit of quantification was
0.89 mg L1.
Results
Milk cannot be analysed directly by ICP-MS because
it is an emulsion containing solid particles that would
clog the nebulizer. A prerequisite of a successful
quantification of iodine in the milk is the development
of a sample preparation procedure. For this purpose an
approach based on the extraction of iodine containing
into an aqueous phase (whey), in the solid particles
(casein) and fat by ultracentrifugation was investigated.
The evaluation of the extraction efficiency was
based on the comparison of the iodine concentration in the milk whey, in the casein and in the fat with
that in the whole milk. Therefore a reliable method for
the determination of iodine in these matrices was
required.
The experiments indicated that the digestion of a milk
sample with diluted ammonia in an open vessel using a
focussed microwave field could be the basis of a simple
method yielding accurate results. Under the optimized
working conditions (0.5% ammonia solution, microwave power of 45 W, 2 min and 30 s) a transparent
solution could be fed directly into an ICP-MS. This
procedure was used for the whole milk, the milk whey,
the fat and for the casein.
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L.M. Fernández-Sánchez et al. / Journal of Trace Elements in Medicine and Biology 21 (2007) S1, 10–13
13
Determination of iodine in the milk
Acknowledgements
Two series of samples were investigated: (i) milk
samples from different woman (14 samples), and (ii)
different infant formulas (27 samples). Such a choice
was judged sufficiently representative for quantification
of iodine in milk.
The milk samples were subjected to ultracentrifugation and the total iodine in the milk whey, in the
casein and in the fat was compared with the iodine
concentration in the milk sample. Results are shown in
Tables 1 and 2.
In the human milk the values found were
between 144793.2 mg kg1, whereas in the infant
formulas the concentrations were lower, with an average
value of 53.3719.5 mg per 100 g sample. The values
found in the human milk are similar to the literature
values [8].
The differences between samples can be due to the
mother feeding.
L.F.S. acknowledges the research Grant of the Caixa
Galicia. We thank Prof. A. Bermejo (University of
Santiago) for valuable discussions.
Conclusions
For both types of samples the bigger amount of iodine
is in the whey fraction, between 80% and 90% whereas
in the fat there is about a 2% of the total iodine and in
the casein fraction the levels are between 5% and 10%
depending on the type sample.
The major difference between the breast milk and
infant formula is the presence in the latter of a
macromolecular compound comprising more than
50% of the iodine present in the preparation. The infant
formulas are similar to the human milk in the iodine
distribution in the different milk fractions. The different
levels observed for the human milks can be due to the
mother feeding.
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