Safety evaluation of certain food additives - ipcs inchem

SULFITES: ASSESSMENT OF DIETARY EXPOSURE 225
headspace, another direct ion exchange and the third direct ion exclusion) were
used to determine total sulfites in different foods. All methods produced similar
results and could detect sulfites at levels as low as 1 μg/g in four of the five types
of food (Lawrence et al., 1990). An HPLC method with indirect photometry was
reported to be reliable to determine sulfur dioxide levels of 5–10 mg/kg in foods
(Pizzoferrato et al., 1990, 1998). An alternative chromatographic method based
upon a combination of a modified Monier-Williams procedure and an ion
chromatographic separation and quantification of total sulfite in foods was
developed by Ruiz et al. (1994).
A differential pulse polarographic method (AOAC International, 1995b) has
been collaboratively tested and is applicable to the determination of sulfur dioxide
levels of 10 mg/kg in shrimp, orange juice, peas, dried apricots and dehydrated
potatoes. Alternative chemical methods for the determination of sulfites include flow
injection analytical systems coupled with spectrophotometric, electrochemical and
chemiluminescence detections (Sullivan et al., 1986; Lin & Hobo, 1996; Decnop-
Weever & Kraak, 1997; Safavi & Haghighi, 1997; Corbo & Bertotti, 2002; Araújo et
al., 2005) and capillary electrophoresis (Trenerry, 1996; Masár et al., 2004).
Methods based on capillary electrophoresis have often been considered faster and
more cost effective than other instrumental techniques, with the added advantage
that most determinations can be carried out using the same fused silica capillary
column. The method described by Trenerry (1996) had a limit of detection of 5 mg/
kg and was found to be suitable for measuring sulfite content in a variety of foods
and beverages, including samples that are not traditionally analysed by the Monier-
Williams procedure. Perfetti & Diachenko (2003) described a method for
determining sulfite in dried garlic. Garlic is extracted with a hydrochloric acid
solution to inhibit the formation of allicin, which interferes with the determination of
sulfite. After cleanup of the extract on a C18 solid-phase extraction column, sulfite
is converted to hydroxymethylsulfonate by adding formaldehyde and heating to
50 °C. Hydroxymethylsulfonate is determined by reversed-phase ion-pairing liquid
chromatography with post-column detection. Recovery of hydroxymethylsulfonate
from spiked garlic averaged 94.8%, with a coefficient of variation of 3.8%.
In conclusion, several methods are available for the determination of
sulfites in foods and beverages, the choice of method depending, among other
factors, on the matrix to be analysed and the expected concentration of sulfite.
The most common methods in use to date involve distillation of sulfur dioxide from
a highly acidified sample, followed by titration, colorimetric, polarographic or ion
chromatographic determination. The iodometric titration methods are not
considered very useful for low analyte concentrations, and the enzymatic methods
using commercial kits offer less sensitivity. To fill the gap when the Monier-Williams
method is not applicable, alternative methods based on HPLC, ion chromatography,
capillary electrophoresis and flow injection analytical techniques have been
developed. In this context, various detection techniques, such as spectrophotometry,
amperometry, potentiometry and chemiluminescence, have been
applied. Whatever test procedures have been adopted by laboratories, they need
in-house validation, and the results should be compared with a reference method.
It is essential for laboratories to implement a well documented internal quality control