Page 131 - Analytical method for food addtives

E220–8: Sulphites 81

• Dried fruit 1.0 g of sample/50 mL of water
• Jam 5.0 g of sample/50 mL of water
• Spices 0.1 g of sample/50 mL of water
• Dried potato products 2.0 g of sample/50 mL of water
Take 100 µL to 500 µL of these solutions for enzymatic determination.

Determination
Perform the determination according to Table 8.1 at a temperature of 20 °C to
25 °C in a quartz cell usually with a sample volume of 100 µL. If the sample
volume is different from 100 µL adjust the volume of added water so that the final
volume of water and sample is 2.00 mL. If the reaction has not stopped, continue
to read the absorbance at intervals of 2 min until the change in absorbance is
constant. If the absorbance decreases constantly, extrapolate the absorbance back
to the time of addition of the sulphite oxidase suspension to estimate the A to be
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used. (For further details see BS EN 1988–2:1998.) 6

Analysis of foodstuffs with sulphite (total) content ≥≥ ≥≥ ≥10 mg/kg using
differential pulse polarographic method 8

Scope
Differential pulse polarographic method for determination of ≥10 µg total SO /g in
2
shrimp, orange juice, peas, dried apricots and dehydrated potatoes.

Principle
SO is purged with N from acidified test sample, collected in electrolyte-trapping
2 2
solution and then determined by differential pulse polarography.
(Notes:
1 Analyst must construct purge-trap apparatus and ensure proper operation by
analysing aqueous SO solutions before analysing test samples.
2
2 System must be purged with N between test samples to remove residual SO .
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3 Analysis must be completed without undue delay; aqueous solutions of
sulphites are unstable.)

Procedure
Test sample preparation
Use open-pan balance (Mettler P1200 [replaced by PM2000], sensitivity 10 mg
per division, or equivalent) to weigh representative test sample (≥10.00 g) into
200 mL Erlenmeyer. Add c. 0.5 g antifoam and then add 5 % alcohol so total
weight of mixture is 100.00 g. Stopper and shake Erlenmeyer, or if necessary
homogenise to obtain fine suspension. Complete test sample preparation quickly
to minimise oxidation of SO by atmosphere O .
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