Page 266 - Analytical method for food addtives

176 Analytical methods for food additives

14.5 Appendix 1: method procedure summaries (analysis of
1
orange drinks )

GC–FID method

Reagents and apparatus
a Diazomethane test solution: 2 g of N-nitrosomethylurea was weighed into a
50 mL Nessler tube and 20 mL ether was added and mixed well. The solution
was cooled with ice-cold water and 205 mL 20 % NaOH was carefully added,
gently mixed and the Nessler tube was capped loosely. It was allowed to stand
with occasional gentle mixing until the bubbling of gas ceased. The upper
layer was transferred to a flask and dehydrated with a small amount of solid
NaOH.
b Adipic acid standard solution: 1000 µg/mL. 100 mg adipic acid was dis-
solved in 100 mL acetone.
c FID gas chromatograph: Yanco G-80 with strip chart recorder. Operating
conditions: temperatures (ºC) – column 100, detector 200, injection port 200;
nitrogen carrier gas flow c. 25 mL/min.
d GLC column: Glass, 200 cm × 3 mm, packed with 5 % DEGS (diethylene
glycol succinate) + 1 % H PO on 80–100 mesh Chromosorb W.
3 4
Extraction and derivative formation
10 g sample was weighed, 20 mL water was added and the pH was adjusted to >10
with 1 N NaOH. If the sample was insoluble in alkali it was mixed in a Waring
blender until it was well suspended. 50 mL of ethyl ether was added and shaken
vigorously. The layers were allowed to separate; the upper layer was discarded and
the lower layer was re-extracted with 50 mL ether and shaken vigorously. The pH
was adjusted to <2 by adding 2 mL 1 N H SO . The solution was saturated with
2 4
NaCl and the adipic acid was extracted by vigorous shaking with 3 × 50 mL
portions of ether. The water layer was discarded and the ether was dried with
anhydrous Na SO . The ether layer was filtered and concentrated to <3 mL in a
2 4
vacuum at 35 ºC and diluted to 3 mL with acetone and the adipic acid was
methylated by adding 2 mL diazomethane reagent to make a final volume of 5 mL.
An aliquot was injected into the gas chromatograph.

Preparation of calibration graph
Standard solution was pipetted into separate tubes in quantities of 0, 0.5, 1.0, 1.5,
2.0, 2.5 and 3.0 mL. Each was diluted to 3 mL with acetone and 2 mL of
diazomethane test solution was added to prepare solutions containing 0, 500, 1000,
1500, 2000, 2500 and 3000 µg adipic acid/5 mL, respectively. Aliquots were
injected into chromatograph and peak height (mm) was plotted against µg adipic
acid/mL.