Page 217 - Analytical method for food addtives

E310–12: Gallates 145

(b) Chromatography – Using sample loop injection valve, inject 10 µL sample
extract and elute with solvent gradient programme for test extracts. Before and
after every 3–4 test injections, or more frequently if differences between
standard peak heights are found to be >5 %, inject 10 µL antioxidant working
standard solution (10 µL/mL) and elute with solvent gradient programme for
standards. For analyte peaks off scale or >3x standard, quantitatively dilute
test extract with 2-propanol-acetonitrile (1 + 1) and reinject. Identify peaks by
comparison with retention times of standard.
For reagent blank determination, take 25 mL saturated hexane and follow
extraction (a), from ‘. . .extract with three 50 mL portions of saturated
acetonitrile.’ Inject 10 µL reagent blank extract and elute with solvent gradient
program for samples. The reagent blank should have no peaks interfering with
antioxidant determination.
Use electronically determined peak height, or measure peak height to
0.1mm, using blank gradient chromatogram as guide to follow baseline.
Determine antioxidant peak heights and average antioxidant standard peak
heights (from duplicate injections before and after test injection, corrected for
gradient blank).

Calculation
Calculate concentration of antioxidant as follows:
Antioxidant, µg/g = (R /R ) × (C /W ) × D [11.1]
x s s x
where:
R and R are peak heights from test portion and standard, respectively
x s
C is concentration standard, µg/mL
s
W is test portion weight, g/mL, in undiluted 10 mL test extract
x
D is dilution factor, if solution injected is diluted
(For further information see AOAC official method 983.15.)