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AOAC FIRST ACTION 2012.22
MULTI LABORATORY TESTING
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E.
Preparation of standards
Warning: Vitamin C is sensitive to light and oxygen, conduct operations under subdued
light, or use amber glassware. Keep all solutions away from direct light.
a.
Ascorbic acid stock solution (500 µg/mL).-
Into a 25 mL amber glass volumetric
flask, weigh 12.5 mg ascorbic acid. Dissolve and make up to volume with TCEP
solution. This solution can be kept for 3 months if stored at 4 °C away from light.
b. Ascorbic acid intermediate standard solution (50 µg/mL).-
Into a 10 mL amber glass
volumetric flask, pipet 1.0 mL of stock solution. Make up to volume with TCEP
solution. This solution can be used for 1 month if stored at 4 °C away from light.
c. Ascorbic acid calibration standard solutions (0.5, 1.0, 2.0, 3.0, 5.0, 7.5, 10.0 µg/mL).-
Into 10 mL amber glass volumetric flasks, pipet 0.1, 0.2, 0.4, 0.6, 1.0, 1.5 and 2.0
mL of intermediate standard solution. Make up to volume with mobile phase.
F.
Sample preparation
a. Reconstitute powder samples
i. Weigh 25.0 g ± 0.1 g (m1) of powder into a brown glass 250 mL beaker. Add
10 mg TCEP
ii. Add 200.0 g ± 0.1 g (m2) warm water (40 °C ± 5 °C). Mix well until complete
dissolution making sure there are no lumps.
Note: the powder samples must be reconstituted freshly before the analysis. Discard any
unused portion.
b. Extraction
i. Weigh 2.0 g ± 0.1 g (m) of liquid or reconstituted sample into a 10 mL (V
1
) amber-
glass volumetric flask.
ii. Add 4 mL of TCEP solution and 2 mL of TCA 15%.
iii. Bring up to volume with water.
iv. Filter solution through folded paper filter.
v. Transfer 1.0 mL (V
2
) of filtrate into a 10 mL (V
3
) amber glass volumetric flask
containing 1 mL acetate solution (pH 5.4) and bring up to volume with mobile
phase.
Filter about 2 mL through 0.22 µm membrane into a LC vial.
2012.22/VitC-03 (February 2016) - MLT
FOR ERP USE ONLY
DO NOT DISTRIBUTE