Page 123 - Analytical method for food addtives

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E220–8: Sulphites

8.1 Introduction
The major food groups contributing to dietary intake of sulphites consist of a wide
variety: 15–500 mg/kg (dried fruit 600–2000 mg/kg; liquid pectin, horseradish
pulp 800 mg/kg) and soft drinks 20 mg/kg (lime and lemon juice, ‘barley water’
350 mg/kg; concentrated grape juice 2000 mg/kg; beer and cider 20–200 mg/kg;
wines 200–260 mg/kg). The acceptable daily intake (ADI) for sulphites (expressed
as sulphur dioxide) is 0.7 mg/kg body weight.

8.2 Methods of analysis
There are numerous methods published for the determination of sulphites in
foodstuffs. The majority of these methods are for the determination of sulphur
dioxide in foodstuffs. Quantitative methods for the determination of sulphur
dioxide fall into two groups, direct and indirect methods. The former include
titrimetric, polarographic, electrometric and colorimetric procedures, the latter
generally involve separation by distillation in an inert atmosphere followed by
absorption of the sulphur dioxide in an oxidising agent, typically iodine or
hydrogen peroxide. The estimation is completed by volumetric, gravimetric,
colorimetric or electrochemical procedures. Both types of methods may be used to
measure free and total sulphur dioxide. 1
Methods that have been developed for sulphites in foodstuffs include the
2–5
6,7
Monier–Williams method, enzymatic, differential pulse polarography, ion
8,9
exclusion chromatography (IEC), 10,11 flow injection analysis (FIA), 12–15,20 sequential
injection analysis (SIA), HPLC, capillary electrophoresis methods 18,19 and
16
17