Page 267 - Analytical method for food addtives

E355–7, E359: Adipic acid and its salts 177

14.6 Appendix 2: method procedure summaries: analysis of
starch 8
9
GC–FID method (total adipate )

Sample preparation
50 mg of the acetylated adipic cross-linked starch sample was weighed accurately
in a glass reaction tube, and 1.5 mL distilled water and 1.0 mL aqueous solution
containing 0.05 mg pimelic acid/mL were added. The reaction tube was shaken to
disperse the sample and 2.5 mL of 4 M NaOH were added. Agitation of the
reaction tube continued in order to dissolve the starch sample. The reaction tube
was closed and the adipyl–starch ester bond was saponified by continually rotating
the tube for at least 5 min. 1.0 mL of conc HCl was added and the mixture was
homogenised. 5 mL ethyl acetate were added, the tube was closed and shaken
vigorously for 1 min to extract the adipic acid and pimelic acid into the ethyl
acetate.*After phase separation the (upper) ethyl acetate layer was transferred with
a glass Pasteur pipette into a clean reaction tube. The ethyl acetate extraction of the
aqueous solution was repeated 3 times and the ethyl acetate fractions were
collected. These collected fractions were evaporated to dryness with a stream of
nitrogen in a Pierce Reacti-Vap evaporator at a temperature of 30 ºC in a water
bath.

Silylation
After that 0.3 mL of acetonitrile were added to the dry residue and the reaction tube
was placed in an ultrasonic bath for several minutes to dissolve the residue. 0.3 mL
of BSTFA/1 % TMCS solution was added and the mixture was homogenised again
in the ultrasonic bath for several minutes. (BSTFA = bis-(trimethylsilyl)-
trifluoroacetamide, TMCS = trimethylchlorosilane.) After reaction time of at least
30 min in a water bath at a temperature of 30 ºC, 0.3 µL of the reaction mixture was
injected into the capillary GC.
GC conditions

Column WCOT-fused silica CP-sil 5CB, 50 m × 0.32 mm, 0.12 µm
film
Carrier gas Helium (pressure 0.7 bar)
Injection Cold on-column
Oven temperature Programmed: 130 ºC for 1 min, 5 ºC/min to 190 ºC, 25 ºC/
min to 290 ºC for 5 min then cooled to 130 ºC
Detector FID at 300 ºC (hydrogen pressure 0.5 bar, air pressure 1.0 bar)