Effect of phosphonium and arsonium salts on the differential-pulse polarograms of three permitted synthetic food colouring matters
The shifts in peak potential and the changes in peak current on adding 750 µg ml–1 of tetraphenylphosphonium chloride, tributylmethylphosphonium iodide, triphenylbutylphosphonium bromide, tributylbenzylphosphonium chloride, triphenylmethallylphosphonium chloride, triphenylmethylphosphonium bromide, triphenylethylphosphonium iodide, tetrabutylphosphonium chloride and tetraphenylarsonium chloride to solutions of Brilliant Blue FCF, tartrazine and Yellow 2G at pH values between 2 and 9 were compared.
For Brilliant Blue FCF large, regular, negative potential shifts were obtained in acidic media owing to the presence of these compounds. In neutral media the sizes of the negative shifts decreased, and potential shifts in the positive direction were obtained in alkaline media. For tartrazine the negative potential shifts tended to be relatively small in acidic and alkaline media, but were larger at intermediate pH values. For Yellow 2G the negative potential shifts were large in acidic media, some decrease was seen at intermediate pH values and an increase in the negative potential shift was observed again in alkaline solution. The tartrazine peak was split into two peaks at intermediate pH values (4–6) in the presence of some of the onium compounds. The largest changes in potential, in general, were obtained with tetraphenylphosphonium chloride, but the addition of other phosphonium and arsonium compounds might be useful in identifying food colouring matters in some situations.
In general, on addition of an onium compound, the peak currents of Brilliant Blue FCF and Yellow 2G were reduced in size, whereas those for tartrazine were sometimes increased. These changes can be used for identification purposes.