A differential pulse polarographic method has been developed for
the determination of ascorbic acid and food colours in the same
solution. Aniline, sulphanilic acid and naphthionic acid were
shown to be formed from particular food colours: visible spectrophotometric
methods involving diazotization and coupling with N-l-naphthylethylenediamine
dihydrochloride.were developed for monitoring their formation.
The method is not subject to interference from the other amines
formed from the cleavage of the azo bonds. Ammonia was shown to
be present in the degraded solution and an indophenol method was
developed for following its formation.
These methods have been used to monitor permitted food colouring
matters and ascorbic acid during interaction in accelerated light
and heat degradation studies in the presence and absence of EOTA.
Heat degradation studies were also carried out in the absence of
EOTA was found not only to stabilise ascorbic acid but also to
stabilise food colouring matters in the presence of ascorbic acid.
Full yields of ammonia were obtained from the degradation of azo
groups via sulphanilic acid and naphthionic acid during the light
degradation studies. Interaction of food colours and ascorbic acid
has also been shown to occur at room temperature in the dark and to
yield ammonia and simple amines.
In the heat degradation studies (130°C) relatively low yields of
amines and ammonia were obtained despite complete visible degradation
of food colours. This indicated the formation of more complex nitrogen
EOTA was shown to stabilise acetamido groups from photolytic
hydrolysis in several drug compounds as well as in the food
colouring matters Red 2G and Black PN.
A rapid differential pulse polarographic method for the
determination of food colours in boiled sweets directly without
prior separation or extraction procedures has been developed.
A detector cell designed and constructed in our workshops and
previously used with a glassy carbon electrode has been adapted very
successfully for use with a sessile mercury drop electrode. The
use of the system in flow injection analysis has been demonstrated
by determining food colours in the reductive and oxidative modes.
Ascorbic acid, sulphite and other species have also been determined.
In the determination of ascorbic acid deoxygenation is not necessary.
A Doctoral Thesis. Submitted in partial fulfilment of the requirements for the award of Doctor of Philosophy of Loughborough University.