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© 2015 AOAC INTERNATIONAL
(
2
)
Mobile phase B.—
4.0 mL TEA and 250 mL acetonitrile
diluted with 750 mL laboratory water and pH adjusted to 5–7 with
about 1.25 mL concentrated formic acid. Expiration 1 week in
tightly stoppered container.
(
3
)
Mobile phase C.—
4.0 mL TEA and 750 mL acetonitrile
diluted with 250 mL laboratory water and pH adjusted to 5–7 with
about 1.25 mL concentrated formic acid. Expiration 1 week in
tightly stoppered container.
(
4
)
2.5% Acetonitrile in H
2
O (mobile phase D).—
50 mL
acetonitrile diluted to 2000 mL with laboratory water. Expiration
1 week in tightly stoppered container.
(
5
)
10% Acetonitrile in H
2
O.—
150 mL acetonitrile diluted
to 1500 mL with laboratory water. Expiration 1 month in tightly
stoppered container.
(
6
)
30% Acetonitrile in H
2
O SPE elution solvent.—
30.0 mL
acetonitrile diluted to 100 mL with laboratory water. Expiration
1 month in tightly stoppered container.
(
7
)
50% Acetonitrile in H
2
O, column cleaning and storage
solution.—
500 mL acetonitrile diluted to 1000 mL in a volumetric
flask. Expiration 6 months.
(
8
)
25% Ethanol.—
50 mL ethanol diluted to 200 mL with
laboratory water. Expiration 1 year in tightly stoppered container.
(
9
)
0.40% Potassium cyanide for samples with 5 mL final
dilution volume.—
Dissolve 0.02 g potassium cyanide in and dilute
to 5 mL with 0.25 M sodium acetate buffer. Make fresh daily before
use.
(
10
)
1% Potassium cyanide.—
Dissolve 0.25 g potassium
cyanide in and dilute to 25 mL with laboratory water. Prepare fresh
daily before use.
(
11
)
Resolution test solution for determining appropriate
gradient conditions when a new analytical column is installed
.—
Weigh about 0.005 g riboflavin onto a weigh paper. Transfer to a
100 mL volumetric flask and dilute to volume with 10% acetonitrile
solution. Stir to dissolve. Mix equal amounts of riboflavin solution
with the highest concentration vitamin B
12
working standard.
Expiration: 1 week.
(
12
)
0.25Msodiumacetate buffer.—
Dissolve 41 g sodiumacetate
anhydrous or 68 g sodium acetate trihydrate in approximately
1800 mL laboratory water. Adjust pH to 4.5 with concentrated
acetic acid. Dilute to 2000 mL with laboratory water. Expiration
3 months.
(
13
)
6% Taka-diastase.—
Dissolve 0.6 g taka-diastase in 10 mL
water. Prepare fresh daily before use.
(
b
)
Standards.—
Prepare all standards under UV shielded
fluorescent lights and store at 2–8°C in tightly stoppered volumetric
flasks.
(
1
)
Vitamin B
12
stock standard (10000
μ
g/L).—
Accurately weigh
the appropriate amount of vitamin B
12
USP reference standard to
give a stock standard concentration of 10000
m
g/L. Dissolve in and
dilute to 100 mL with 25% ethanol. Expiration 6 months.
Use the following equation to calculate the amount of vitamin B
12
reference standard that should be weighed:
S
w
= 10000 × 0.1 × 1/P
where S
w
= amount of vitamin B
12
standard to be weighed in
mg; 10000 = desired stock standard concentration in μg/L; 0.1 =
dilution volume in L; P = purity of the USP reference standard in μg
Figure 2011.10B. System setup and configuration:
Configuration 2.
Figure 2011.10A. System setup and configuration:
Configuration 1.
Table 2011.10D. Guidelines for loading sample filtrates onto
SPE cartridges
a
Vitamin B
12
concentration
in RTF product, μg/kg
Volume of filtrate loaded
onto SPE cartridge, mL
Final dilution
volume, mL
<1
80
5
1–10
70–80
10
11–20
50–60
10
21–50
20–40
10
a
Do not load more than 60 mL adult and pediatric nutritionals onto an
Alltech C
8
or C
18
cartridge.
Candidates for 2016 Method of the Year
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