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(b).
Ascorbic acid intermediate standard solution (50 µg/mL).-
Into a 10 mL amber
52
glass volumetric flask, pipet 1 mL stock solution. Make up to volume with
53
TCEP solution. This solution can be used for 1 month if stored at 4 °C away
54
from light.
55
(c).
Ascorbic acid calibration standard solutions (0.5, 1.0, 2.0, 3.0, 5.0, 7.5, 10.0
56
µg/mL).-
Into 10 mL amber glass volumetric flasks, pipet 0.1, 0.2, 0.4, 0.6, 1.0,
57
1.5 and 2.0 mL of intermediate standard solution. Make up to volume with
58
mobile phase to prepare the respective concentrations given above.
59
F.
Sample preparation
60
(a).
Reconstitution of powder samples
.-
61
1.
Weigh 25 g of powder into a brown glass 250 mL beaker, add 10 mg TCEP.
62
2.
Add 200 g warm water (40 °C). Mix well until complete dissolution, make sure
63
there are no lumps.
64
(b).
Extraction.-
65
1.
Weigh 2 g of liquid or reconstituted sample into a 10 mL amber-glass
66
volumetric flask.
67
2.
Add 4 mL TCEP solution and 2 mL TCA 15 %.
68
3.
Bring up to volume with water.
69
4.
Filter solution through folded grade 597
½
or greater filter paper (Schleider &
70
Schuell, Dassel, Germany).
71
5.
Transfer 1 mL of filtrate into a 10 mL amber glass volumetric flask containing
72
1 mL acetate solution (pH 5.4) and bring up to volume with mobile phase.
73
6.
Filter about 2 mL through 0.22 µm membrane into a HPLC vial.
74
G.
Analysis
75
(a).
Chromatographic conditions.-
76
AOAC 2012.22 (FINAL VERSION REVIEW) - JUNE 2016
FOR ERP USE ONLY
DO NOT DISTRIBUTE
AOAC OMB Meeting Book
392