Issue 1241, 1979

Direct differential-pulse polarographic determination of mixtures of the food colouring matters tartrazine-Sunset Yellow FCF, tartrazine-Green S and amaranth-Green S in soft drinks

Abstract

Tartrazine and Sunset Yellow FCF can be determined directly in orangeade by differential-pulse (d.p.) polarography on the addition of pH 9 Britton-Robinson buffer and tetraphenylphosphonium chloride. The tetraphenyl-phosphonium chloride removes the large polarographic maximum obtained with tartrazine at pH > 4 and causes the d.p. polarographic peaks of the two colouring matters to be separated.

Tartrazine in limeade can be determined in a similar supporting electrolyte but these conditions are not suitable for the determination of Green S, which is usually present at a low concentration relative to the tartrazine and for which the d.p. polarographic peak is depressed by the addition of tetraphenylphosphonium chloride. Green S can be determined after adding pH 4 Britton-Robinson buffer and tetramethylammonium chloride to the limeade: the addition of tetramethylammonium chloride gives a better base line in the presence of tartrazine. The solution is then re-adjusted to pH 9 and tetraphenylphosphonium chloride is added in order to determine the tartrazine.

At pH 4 the sugar present in blackcurrant syrup gives a small d.p. polarographic peak at the same potential as Green S. At pH > 6 the peak of the sugar disappears but amaranth gives a broad polarographic maximum. This maximum is suppressed at pH 7.8 by the addition of tetramethylammonium chloride. Under these conditions the Green S peak is separate but the small concentrations of Green S normally present in blackcurrant drinks can only just be detected.

The procedures have been tested on soft drinks prepared with known concentrations of colouring matter.

Article information

Article type
Paper

Analyst, 1979,104, 723-729

Direct differential-pulse polarographic determination of mixtures of the food colouring matters tartrazine-Sunset Yellow FCF, tartrazine-Green S and amaranth-Green S in soft drinks

A. G. Fogg and K. S. Yoo, Analyst, 1979, 104, 723 DOI: 10.1039/AN9790400723

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