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(
Note
: It is important that the sodium hydroxide does not absorb
carbon dioxide from the air.) Swirl to mix well. Dilute to volume
with water and mix well. Expiration: 1 month.
(g)
Sodium hydroxide, 4.0% or 1 M (Pump 2).
—Quickly
weigh 160 (±3) g 50% sodium hydroxide into a 2000 mL
volumetric flask containing approximately 1900 mL water.
(
Note
: It is important that the sodium hydroxide does not absorb
carbon dioxide from the air.) Swirl to mix well. Dilute to volume
with water and mix well. Expiration: 1 month.
(h)
6%Metaphosphoric acid.
—Weigh 6.0 g metaphosphoric
acid into a 100 mL volumetric flask. Dissolve and dilute to
volume with laboratory water. Mix well. Store refrigerated.
Expiration: 1 week.
(i)
Phosphatidylinositol extraction solutions.
—Prepare fresh
on day of use.
(
1
)
Chloroform–methanol (2 + 1).
—Mix 60 mL chloroform
and 30 mL methanol.
(
2
)
Hexane–diethyl ether (80 + 20)
.—Mix 80 mL hexane
and 20 mL diethyl ether.
(
3
)
Hexane–diethyl ether (50 + 50)
.—Mix 50 mL hexane
and 50 mL diethyl ether.
(
4
)
Methanol–chloroform–water (75 + 15 + 10).—
Mix
75 mL methanol, 15 mL chloroform, and 10 mL water.
E. Sample Preparation and Extraction
(a)
Sample preparation for free myo-inositol determinations.
—
Prepared samples that are constantly stored at 1–8°C in closed
containers are stable for up to 5 days. After 5 days, samples must
be prepared again.
Thoroughly mix or stir products prior to sampling. For
liquid products, accurately weigh 0.5 to 5 g (±10%) product
into a 100 mL volumetric flask and record the weight to the
nearest 0.0001 g. For powdered products that do not require
reconstitution, accurately weigh 0.25–1.5 g powder into a
100 mL volumetric flask and record the weight to the nearest
0.0001 g. Add approximately 10 to 15 mL laboratory water to
the volumetric flask and swirl or stir to completely dissolve
the powder. For powdered products that are not homogeneous
at the subgram level, reconstitute following the product label
instructions and accurately weigh 0.5 to 5 g reconstituted
product into a 100 mL volumetric flask. Record the weight to the
nearest 0.0001 g. Add enough 0.5% hydrochloric acid to each
sample to adjust the sample pH to 4.5 ± 0.2 and swirl to mix.
Allow the samples to react with 0.5% hydrochloric acid for
a minimum of 2 min and then dilute to volume with laboratory
water. Mix well. Filter samples through Whatman 2V filter
paper into 125 mL Erlenmeyer flasks or appropriate glassware.
(
Note
: Although some samples will filter cloudy, the filtrates
can still be used.) Filter an aliquot of sample filtrate through
a 0.45 μm syringe filter into an autosampler vial.
(b)
Sample preparation for myo-inositol bound as
phosphatidylinositol determinations.—
(
1
)
Extraction
.—Weigh
4 g (±10%) liquid or reconstituted powder product or 1 g (±10%)
homogeneous powder into a 50 mL centrifuge tube and record
the weight to the nearest 0.0001 g. Add 4 mL laboratory water
to 1 g homogeneous powder samples. In a fume hood, add
10 mL methanol and stir for at least 20 min or vortex for at least
1 min and allow samples to set for at least 20 min. Add 20 mL
chloroform and stir for at least 5 min or vortex for at least 1 min
and allow samples to set for at least 5 min. If large clumps form
when chloroform is added, cap tube and shake well for at least
1 min to mix sample. Add 5 mL 6% metaphosphoric acid and
Table 2011.18B. SLV accuracy (spike recovery) data for myo-inositol
Sample type
No. of replicates
(duplicates on
multiple days)
Native level,
mg/100 g RTF
Spike level,
mg/100 g RTF Recovery, % RSD, %
Free myo-inositol
Child formula powder, unfortified
12
0.0426
1.89
101
2.78
Infant formula powder soy-based
12
4.18
14.9
98.2
2.47
Infant formula powder partial hydrolyzed milk-based
12
3.35
15.2
102
3.00
Infant elemental powder, unfortified
12
0.00
1.74
93.9
3.00
Infant elemental powder, unfortified
6
0.00
1.09
93.2
1.54
Infant elemental powder, unfortified
6
0.00
0.390
90.2
3.14
Adult nutritional powder milk-based
12
0.409
65.0
101
2.64
Adult nutritional RTF high protein
12
0.042
61.4
96.3
3.27
Myo-inositol bound as phosphatidylinositol
Infant formula (NIST SRM 1849a)
6
11.1
a
7.3
77.1
13.2
Infant elemental powder, unfortified
6
0.00
0.294
87.3
6.88
Child formula powder
6
0.443
0.340
90.0
15.7
Infant formula powder soy-based
6
2.48
3.22
81.9
0.21
Infant formula powder partial hydrolyzed milk-based
6
0.247
0.152
79.9
7.51
Infant formula powder partial hydrolyzed soy-based
6
1.94
2.47
72.8
5.18
Adult nutritional powder milk-based
6
1.43
1.54
75.7
3.23
a
Results in mg/kg powder.
148