Page 19 - Analytical method for food addtives

4 Analytical methods for food additives

1.5 Appendix: method procedure summaries

Analysis of soft drinks 2

Sample preparation
Accurately weigh 10 g of sample into a 25 mL beaker and adjust to pH 7.0 with
0.1 mol/L sodium hydroxide.

Extraction
Transfer neutralised sample to centrifuge tube. Rinse beaker and pH electrode with
2 × 5 mL portions of water and transfer washings to centrifuge tube. Add 5 mL
0.1 mol/L cetylpyridinium chloride in water, mix and add 10 mL of water-
saturated n-butanol. Shake vigorously for 10 min on mechanical shaker. Centrifuge
at 1000 g for 5 min and transfer upper organic layer to a 25 mL volumetric flask
using a Pasteur pipette. Repeat the procedure with three 5 mL portions of water-
saturated n-butanol.
Make the combined n-butanol extracts up to 25 mL with water-saturated
n-butanol. Accurately dilute an aliquot of the filtrate with an equal volume of
mobile phase (1 L + 1 L dilution of mobile phase A and solution B). Mix and filter
a portion through a filter.

Quantitative determination: HPLC
Load 20 µL of sample extract onto column and use gradient (linear) elution to
achieve optimum separation.
Column Spherisorb C8, 250 × 4.6 mm, 5 µm
Guard column packed with 40 µm reverse phase material (e.g. Perisorb RP8
30–40 µm
Mobile phase 60 % Solution B and 40 % Solution A linear gradient to 80 %
Solution B and 20 % Solution A after 20 min
Flow rate 1.5 mL/min
Detector 430 nm
Solution A Phosphate buffer and water are diluted 50 mL + 850 mL, and
this solution is de-gassed. To the de-gassed solution, 50 mL
of cetylpyridinium chloride solution is added and the final
solution made to 1 L in a volumetric flask. The solution is de-
gassed before the addition of cetylpyridinium chloride
solution to avoid frothing.
Solution B Cetylpyridinium chloride solution is diluted 50 mL to 1 L
with a 1 L + 1 L dilution of acetonitrile and methanol.