Eleven food colouring matters, alizarin fluorine
blue and some indicator dyes were studied using adsorptive
stripping voltammetry at a hanging mercury drop electrode.
The effect of adding gelatin and phosphonium salts on the
stripping peak potentials and peak currents was studied.
In the case of 7 food colours 25 ppm of gelatin was
sufficient to obtain a full shift and full enhancement of
peak height. The largest potential shifts were obtained
with Chocolate Brown, indigocarmine, Ponceau 4R, Red 2G and
quinoline yellow. The effect is pH dependent and the
addition of gelatin can be used in the identification of
Alizarin fluorine blue (AFB) in pH 4.7 acetate
buffer gives two peaks, the first due to adsorption of
copper(II)-AFB and the second peak due to adsorption of AFB
itself. The peak heights are dependent on pH and on
electrolyte concentration. Addition of AFB to the
solution containing lead(ll) enhances the peak owing to
adsorption of the lead-AFB complex. Addition of
lanthanum(III) eliminates the second peak and the signal is
not enhanced by the addition of fluoride. Enhancement of
the peak at -1.05 V for a zinc solution due to addition of
AFB indicates that Zn-AFB complex can be accumulated.
Compound related to AFB, namely xylenol orange was
very poorly adsorbed on mercury. Studies of metal
complexes of Mordant Red 74, a selective reagent for
beryllium were affected by precipitation although the
compound gives two large peaks at pH 4 on its own.
2-, and 4-nitrobenzyltriphenylphosphonium bromides
which were electroactive were shown to adsorb at mercury.
Comparison was made of the effect of these phosphonium
compounds and that of those which are not electroactive on
the adsorptive stripping voltammograms of tartrazine.
A Master's Thesis submitted in partial fulfilment of the requirements for the award of Master of Philosophy of Loughborough University.