Analyst June 1983 Vol. 108 691-700 691 Differential-pulse Polarographic Monitoring of Permitted Synthetic Food Colouring Matters and Ascorbic Acid in Accelerated Light Degradation Studies and the Spectrophotometric Determination of the Ammonia and Simpler Amines Formed Arnold G. Fogg and Abdulhadi M. Summan Chemistry Defiartment Loughborough University of Technology Loughborough Leicestershire LE 11 3T U Permitted food colouring matters and ascorbic acid were determined by differential-pulse polarography to monitor their interaction during light degradation studies at pH 5.5 in acetate buffer containing EDTA. Reduc-tive splitting of azo bonds in the food colours was apparent from the formation of amines such as aniline sulphanilic acid and naphthionic acid which were determined spectrophotometrically using diazotisation methods.These amines were shown to be degraded further in the light to yield ammonia, which was determined spectrophotometrically as indophenol. Keywords ; Food colouring matters ; degradation ; ammonia ; amines ; difleeren-tial-pulse polarography Ascorbic acid is added to certain soft drinks as a vitamin and/or as an antioxidant. Most soft drink preparations are coloured artificially with permitted food colouring matters and problems can arise due to interaction of some or all of the food colouring matter with ascorbic acid. This is particularly troublesome should the bottled soft drink be displayed for example, in bright sunlight in a shop window or on a garage forecourt. The problem is exacerbated in countries that experience strong sunlight which has to be taken into account when exporting soft drinks.Studies of the determination of food colouring matters and their degradation products are being undertaken in this laboratory. Diff erential-pulse polarography has been used to determine mixtures of food colouring matters1-3 and to monitor the degradation of individual food colouring matters in accelerated light and heat degradation ~ t u d i e s . ~ ~ ~ The addition of tetraphenylphosphonium chloride which alters the peak potentials of some food colours is useful in effecting separation of overlapping polarographic peak~.l-~#~ The use of voltam-metry with a glassy carbon electrode has been assessed with static and flow injection systems.6J The formation of Red 10B from the permitted food colour Red 2G by heat degradation has been monitored p~larographically.~ The interaction of permitted food colouring matters with ascorbic acid during an accelerated light degradation experiment has been studied here.Ascorbic acid gives a polarographic oxidation wave a t a dropping-mercury electrode with a half-wave potential of +0.06 V (pH 5.5) and can be determined polarographically at the same time as the food colours are determined by means of their reduction waves at more negative potentials. As ascorbic acid is a reducing agent it was expected that reductive splitting of the azo group to form the corresponding amines might occur in the presence of intense light and this was found to be so. For this reason the feasibility of using spectrophotometric methods to detect and deter-mine these amines was investigated.The structures of the permitted synthetic food colouring matters containing azo bonds are given in Table I. Clearly if reductive splitting occurs Red 2G should give aniline Sunset Yellow FCF Yellow 2G tartrazine Black PN and Brown FK should give sulphanilic acid and amaranth carmoisine Ponceau 4R and Chocolate Brown HT should give naphthionic acid in addition to larger amines. Aniline and sulphanilic acid are known to diazotise and couple with N-1-naphthylethylenediamine in dilute hydrochloric acid solution but naph-thionic acid was found to require more concentrated acid conditions in order to react and a satisfactory procedure was developed for this. Certain other large amines were tested an 692 FOGG AND SUMMAN DIFFERENTIAL-PULSE POLAROGRAPHIC Analyst VoZ.108 TABLE I STRUCTURES OF PERMITTED FOOD COLOURING MATTERS WITH AZO GROUPS Food colour Red 2G . . Sunset Yellow FCF Yellow 2G . . Tartrazine . . Structure OH NHCOCH3 eN=NIYl NaS03 ' ' S03Na HO NaS03 S03Na CI QC' S O ~ N ~ S O ~ N ~ OH NHCOCH3 NaSO, Black PN S03Na S03Na NH2 Brown FK (mixture of about six compounds*) R = H -26% R = CH3 -17% S03Na *Additional azo e.g. N H 2 + N = N e groups occur here in R" other constituents H p S03Na Amaranth NaS03 B N = \ S03N Jzcrte 1983 MONITORING OF FOOD COLOURS AND ASCORBIC ACID TABLE I-continued Food colour Carmoisine . . . . Ponceau 4R . . 693 Structure OH S03Na OH were found not to react under the conditions developed for the spectrophotometric deter-mination of naphthionic acid and it is possible that there is little or no interference in these methods from the other amines formed during the degradation of the food colours shown in Fig.1. Ascorbic acid was found to interfere with the reactions used to produce the spectro-photometric derivatives and any ascorbic acid remaining in the degraded solution was destroyed carefully with potassium permanganate before determining the amine. When these methods were applied to the degradation studies the yields of the simpler amines such as sulphanilic acid were found to increase to almost complete formation with increased time of degradation but then to decrease markedly again.Subsequently aniline, sulphanilic acid and naphthionic acid were shown to degrade under the conditions of the light degradation. Ammonia was shown to be formed and this was determined spectro-photometrically using the indophenol method. In this study the ammonia was distilled before being determined as minor interferences were observed from other degradation products which underwent indophenol-type reactions when the indophenol method was applied directly to the degraded solutions. Experimental Apparatus Polarographic measurements were made with a PAR 174 polarographic analyser (Princeton Applied Research) and a Gould H-2000 X - Y recorder. A three-electrode operation was employed using a dropping-mercury electrode a platinum counter electrode and a saturated calomel reference electrode.Diff erential-pulse polarography was carried out with a forced drop time of 1 s a scan rate of 5 mV s-l and a pulse height of 50 mV. Solutions were deoxygenated by means of nitrogen that had been passed through a vanadium(I1) scrubber. Light degradation studies were carried out in a specially constructed light box in which the sample solutions were held at a uniform close distance from a 500-W lamp (Philips G/74). This apparatus is described in more detail el~ewhere.~ The solutions were deoxygenated with nitrogen gas and were contained in tightly sealed screw-capped autoclavable bottles. Spectrophotometric measurements were made with a Pye Unicam SP600 spectrophoto-meter 694 FOGG AND SUMMAN DIFFERENTIAL-PULSE POLAROGRAPHIC Analyst VOZ.108 Light Degradation Studies Food colour solutions 1000 p.p.m. Dissolve 0.1 g of an authentic food colour sample in water and dilute to 100 ml in a calibrated flask. Acetate bufer solution (PH 5.5). Dilute 62.5ml of 1 M acetic acid solution and 50ml of 1 M sodium acetate solution to 11 and adjust to pH 5.5 with 1 M sodium hydroxide solution. Ascorbic acid - EDTA solution 2% m/V ascorbic acid. Dissolve 2 g of abscorbic acid and 0.05 g of ethylenediaminetetraacetic acid (disodium salt) in water and dilute to 100 ml in a calibrated flask. Ascorbic acid - EDTA solution 0.2% mlV ascorbic acid. Prepare as above to contain the same amount of EDTA but only 0.2 g of ascorbic acid. Solutions for degradation. In the general study of the interaction between food colours and ascorbic acid concentrations of 5 and 100 p.p.m.respectively were used. In attempting to determine the stoicheiometry of the reaction between the food colours and ascorbic acid, solutions 5 p.p.m. in food colour and 1000 p.p.m. of ascorbic acid were degraded in light. In later studies in which the amounts of small amines and ammonia were monitored solutions 10 p.p.m. in food colour and 1000 p.p.m. in ascorbic acid were degraded. In all instances 20 ml of acetate buffer (pH 5.5) were included in the preparation of each 100 ml of solution for degradation. Polarographic Determination of Food Colour and Ascorbic Acid in Degraded Solutions The food colour concentration was determined by applying diff erential-pulse polarography directly to the degraded solutions after deoxygenation.Ascorbic acid was determined similarly but using a 10-fold dilution with water before polarographing for solutions at the higher ascorbic acid concentrations. Spectrophotometric Determination of Amines Sodiwa nitrite solution 0.1% m/V. Hydrochloric acid 1 + 1 V/V. Mix equal volumes of concentrated hydrochloric acid and Sulphamic acid solution 0.5% mlV. Potassium bromide solation 20% m1V. N-1-Naphthylethylenediamine dihydrochloride solution 0.1 yo m/ V . Standard sulphanilic acid solution 1 x 10-4 M. Dissolve 0.433 g of sulphanilic acid in water and dilute to 250 ml in a calibrated flask. Transfer by pipette 5 ml of this solution into a 500-ml calibrated flask and dilute to volume with water. M. Dissolve 0.618 g of naphthionic acid in a small volume of water and 3 ml of 1 M sodium hydroxide solution and dilute to 250 ml with water in a calibrated flask.Transfer by pipette 5 ml of this solution into a 500-ml calibrated flask and dilute to volume with water. Dissolve 0.465 g of aniline in a small volume of water and 2 ml of 1 + 1 V/V hydrochloric acid and dilute to 500 ml in a calibrated flask. Transfer by pipette 5 ml of this solution into a 500-ml calibrated flask and dilute to volume with water. Dissolve 1.58 g of potassium permanganate in 100ml of water in a 250-ml beaker cover with a clock-glass boil gently for 15-20min allow to cool to room temperature filter and collect the filtrate in a flask covered with aluminium foil. Store this solution in the dark. As required dilute 10 ml of this solution to 100 ml.water. Standard naphthionic acid solution 1 x Standard aniline soktion 1 x 10-4 M. Potassium permanganate solution approximately 0.01 M. Procedure for destruction of the excess of ascorbic acid Place an aliquot (10 ml) of degraded solution in a 50-ml conical flask add a few drops (0.4-0.5 ml) of concentrated sulphuric acid and warm slightly. Add 0.01 M potassium permanganate solution dropwise until a faint pink tinge remains 10 s after addition. Trans-fer the solution quantitatively into the calibrated flask to be used for determining amines June 1983 MONITORING OF FOOD COLOURS AND ASCORBIC ACID 695 Procedure for determination of sulfihanilic acid and aniline Transfer by pipette an aliquot of standard sulphanilic acid or aniline solution or degraded food colour solution (previously treated with permanganate if necessary) into a 100-ml calibrated flask add 2 ml of 1 + 1 V/V hydrochloric acid and 2 ml of 0.1% m/V sodium nitrite solution mix and allow to stand for 20 min.Add 2 ml of 0.5% m/V sulphamic acid solution mix and allow to stand for 3 min. Add 2 ml of 0.1% m/V N-l-naphthylethylene-diamine dihydrochloride solution dilute to volume mix and allow to stand for 30min.* Measure the absorbance of this solution at 545 nm. Procedure for determination of naphthionic acid Transfer an aliquot of standard naphthionic acid or sample solution into a 50-ml beaker, adjust the pH to 7.0 if necessary by addition of dilute hydrochloric acid or sodium hydroxide solution and add 2 ml of 0.1% m/V sodium nitrite solution and 2.5 ml of 20% potassium bromide solution.Mix well and add carefully over a period of 5 min to a cooled mixture of 3ml of concentrated sulphuric acid and 3ml of water. Allow the mixture to stand for 3 min add 2 ml of 0.5% m/V sulphamic acid solution mix and allow to stand for 5 min. Add 3 ml of ethanol (96%) and after 3 min transfer quantitatively into a 50-ml calibrated flask containing 4 ml of 0.1 yo m/V N-1-naphthylethylenediamine dihydrochloride solution, dilute to volume and allow to stand for 30 min. Measure the absorbance of the solution at 550 nm. Spectrophotometric Determination of Ammonia Sodium hypochlorite solution. (10-14y0 available chlorine) to 25 ml. Alkaline phenol solution. in water and dilute to 100 ml. Sodium nitrofirusside solution 0.1 yo m/V.Dilute 10 ml of commercial sodium hypochlorite solution Carefully dissolve 30 g of phenol and 20 g of sodium hydroxide Distillation of ammonia from degraded solations Transfer an aliquot (e.g. 25ml) of degraded food colour solution into a 50-ml conical flask add a few drops (0.4-0.5ml) of concentrated sulphuric acid warm slightly and add 0.01 M potassium permanganate solution dropwise until a faint pink tinge remains for 20 s. Transfer the solution quantitatively into an ammonia distillation flask and add 25 ml of 10% m/V sodium hydroxide solution. Distil the ammonia directly into 25ml of 0.1 M hydrochloric acid solution contained in a 50-ml conical flask rinsing the condenser with a small volume of water into the flask after completion.Transfer the solution into a 50-ml calibrated flask and dilute to volume with water. Take aliquots of this solution (e.g. 20 ml) for the indophenol reaction; the pH of the aliquot is adjusted to >7 before adding the reagents. Procedare for spectrophotometric determination of ammonia Transfer by pipette an aliquot of neutral or slightly alkaline standard ammonium chloride solution or sample solution into a 25-ml calibrated flask. Add by pipette in turn with swirling and at 1-2-min intervals 0.2 ml of sodium hypochlorite solution 0.5 ml of alkaline phenol solution and 0.2 ml of sodium nitroprusside solution. Heat the flask at 60-65 "C in a water-bath for 3-5 min to form the indophenol blue. Cool dilute to volume and measure the absorbance at 630 nm. Results Ascorbic acid under these conditions gives a diff erential-pulse polarographic peak at +0.06 V.The necessity of adding EDTA to inhibit oxidation of ascorbic acid by air during the light degradation is illustrated by the results given in Table 11. In the absence of EDTA only 1% of the ascorbic acid in a 100 p.p.m. solution remains after 7 h whereas in * Coupling is only about 50% complete after 30 min for aniline under these conditions,O although good reproducibility was obtained. Similar results were obtained after full coupling in 3-24 h 696 FOGG AND SUMMAN DIFFERENTIAL-PULSE POLAROGRAPHIC Analyst VoZ. 108 the presence of 0.0025~0 of EDTA 76% remains after 64 h. Levels of EDTA greater than 0.005~0 m/V were not used as this distorted the polarographic wave of ascorbic acid.All results reported below were obtained for degradation solutions containing 0.002 5% m/V of EDTA when ascorbic acid was included. When ascorbic acid was omitted so was EDTA. TABLE I1 EFFECT OF EDTA IN STABILISING ASCORBIC ACID (100 p.p.m.) FROM OXIDATION BY AIR DURING LIGHT DEGRADATION (a) Without EDTA-Time/h . . 0 2 10 Remnant of ascorbic acid yo of original . 100 50.0 1.0 (b) With 0.0025~0 of EDTA-Time/h . . . . 0 64 90 132 Remfiant of ascorbic acid % of original 100 76 56 0 The interaction of ascorbic acid and a food colour is illustrated by the example of amaranth in Fig. 1. Graphs are shown for the degradation of ascorbic acid and amaranth separately, and in the presence of each other. Clearly in admixture both compounds degrade signifi-cantly more rapidly which was so for all the food colours.Information for the interaction with ascorbic acid for all the food colours is given in Table 111. For solutions 100 p.p.m. in ascorbic acid the approximate time taken for all the ascorbic acid to be oxidised is given together with the time for half of the food colour to be degraded under these conditions and also in the absence of ascorbic acid. In the former instance the ascorbic acid is degraded before all the food colour has been lost. For solutions 1000 p.p.m. in ascorbic acid the time taken for all the food colour to degrade is also given. The food colours are listed in order of increasing stability under the latter conditions. Time/h Fig. 1. Light degradation in acetate buffer (pH 5.5) of amaranth and ascorbic acid separately and in admixture.Initial amaranth concentration = 10 p.p.m. Initial ascorbic acid concentration = 100 p.p.m. EDTA con-centration = 25 p.p.m. A Amaranth alone; B amaranth in the presence of ascorbic acid; C ascorbic acid alone; and D ascorbic acid in the presence of amaranth J m e 1983 MONITORING OF FOOD COLOURS AND ASCORBIC ACID 697 An attempt to determine the stoicheiometry of the reaction of food colour and ascorbic acid was made for those food colours that degraded rapidly in the presence of ascorbic acid. A typical degradation graph is shown in Fig. 2. The initial degradation of ascorbic acid ceased after the food colour had disappeared visually. This amount of ascorbic acid corresponds to a stoicheiometry of 1:4 for food colour to ascorbic acid for Chocolate Brown HT Black PN and Brown FK.Some time after the disappear-ance of the food colour degradation of ascorbic acid accelerated again and the rate of degradation became more rapid than it would have been in the absence of the food colour degradation products. It may be significant that the time at which the rate of ascorbic acid degradation increases again (10 h see Fig. 2) corresponds with that at which there is a marked increase in the production of ammonia. The yield of ammonia remains essentially constant during the period of ascorbic acid stability (2-10 h). The other food colours gave ratios of 1 2. TABLE I11 LIGHT DEGRADATION OF FOOD COLOURS AND ASCORBIC ACID IN ADMIXTURE Food colour Chocolate Brown HT Carmoisine .. Black PN . . BrownFK Ponceau 4R . . Red 2G Sunset Yellow FCF . . Amaranth . . Tartrazine . . Green S Brilliant Blue FCF . . Patent Blue V . . Yellow 2G Quinoline Yellow . . Approximate time for complete loss of 100 p.p.m. of ascorbic acid/h * . 38 66 80 22 42 90 a . 90 62 66 70 62 80 66 62 * >2 weeks. t Ascorbic acid degrades completely first. p loo 0 0 g 8 m Time for loss of half of food colour in presence of 100 p.p.m. of ascorbic acid/h 62 38 75 18 30 96 36 44 42 56 42 62 60 62 Time for loss of half of food colour in absence of ascorbic acid/ h 73 * * 92 80 * * * * * * * 130 70 Time for loss of all food colour in presence of 1000 p.p.m.of ascorbic acid/h 1 2 2 3 12 23 24 24 42 62 64 64 > 96t >96t 50 0 10 20 Time/h Fig. 2. Light degradation of ascorbic acid (initial concentration = 1000 p.p.m.) in the presence of Chocolate Brown HT (initial con-centration = 6 p.p.m.). EDTA concentration = 26 p.p.m. The solution became colourless after 2 h 698 FOGG AND SUMMAN DIFFERENTIAL-PULSE POLAROGRAPHIC Andyst VoZ. 108 Data on the degradation of sulphanilic acid naphthionic acid and aniline in the presence and absence of ascorbic acid are given in Table IV. The percentage of amine remaining and the percentage yield of ammonia (based on the formation of one ammonia molecule per amine molecule) are given. Naphthionic acid clearly degrades rapidly giving a full yield of ammonia within 16 h even in the absence of ascorbic acid; in its presence this time is halved.Sulphanilic acid is considerably more stable than is naphthionic acid 15 d being required for TABLE IV LIGHT DEGRADATION OF SULPHANILIC ACID NAPHTHIONIC ACID AND ANILINE WITH AND WITHOUT ASCORBIC ACID PRESENT With ascorbic acid Compound Time 1.5 h 5 h 7.5 h 12 h 16h Sulphanilic acid . . l h 3 h 5 h 15h 20h 2 d 4 d 8 d 10 d 12 d 16 d 21 d Aniline . . 7 d 12 d 20 d 25 d Naphthionic acid . . 0 Compound remaining yo 100 27.2 4.2 1.5 0 0 92.2 77.8 73.8 71.7 70.8 62.3 49.3 27.4 19.1 11.3 0 100 6.6 0 --Molar yield of ammonia % 10* 84.1 98.6 100.1 100.6 100.4 9.8 18.5 23.1 26.8 28.3 36.5 45.6 67.4 77.0 87.1 95.7 0 95.9 99.9 --Without ascorbic acid r Compound Molar yield of remaining yo ammonia % 100 10* A \ 62.2 48.4 24.7 85.4 24.7 86.1 4.9 96.6 0 100.2 100 66.6 66.0 61.5 85.8 39.1 11.4 100 0 24.1 24.1 29.3 0 14.8 62.4 91.7 * These results indicate that some ammonia is obtained on heating naphthionic acid with sodium hydroxide solution.The results in this column should be viewed accordingly. complete loss in the presence of ascorbic acid and much longer in its absence. Aniline is much stabler than the other two amines although even for aniline 50% degradation to ammonia was observed after 14 d in the presence of ascorbic acid.In Table V data are given concerning the formation of amine (aniline sulphanilic acid or naphthionic acid) and of ammonia during the degradation of the food colours in the presence of lo00 p.p.m. of ascorbic acid. All the data were obtained after the complete loss of food colour from the solution and after removal of any remnant of ascorbic acid with potassium permanganate. Thus in all instances maximum formation of amine is seen at the f h t measurement time usually after an additional 1 h of light treatment and even by this time ammonia has been formed indicating that some of the amine has already degraded. Clearly ammonia can be formed from both amines formed by cleavage of the azo double bond and this is apparent in the results. Red 2G Sunset Yellow FCF tartrazine carmoisine Ponceau 4R and amaranth all of which contain a single azo group give a 200% yield of ammonia, indicating that not only do the amines that have been determined (aniline sulphanilic acid and naphthionic acid) degrade but also those with more complicated structures formed from the part of the molecule on the other side of the azo bond.This is probably to be expected in view of the increasing ease of degradation from aniline to naphthionic acid. Black PN and Chocolate Brown HT which have two azo groups in their structures give a yield of 400% of ammonia. Brown FK which is a mixture of related compound9 having 1-3 a June 1983 MONITORING OF FOOD COLOURS AND ASCORBIC ACID 699 TABLE V FORMATION OF SIMPLE AMINES AND AMMONIA ON LIGHT DEGRADATION OF A20 FOOD COLOURS I N THE PRESENCE O F ASCORBIC ACID The amines and ammonia were not determined until all traces of the food colour had disappeared visibly.The time for this is given in parentheses with the name of the food colour. The additional times of light treatment before measurement are given. Food d o u r Red 2G (23 h) . . Sunset Yellow FCF (24 h) Tartrazine (42 h) Black PN (2 h). . Brown FK (3 h) Carmoisine (2 h) Ponceau 4R (12 h) Amaranth (24 h) Chocolate Brown HT (1 h) * . Additional time l h 5 h 10h 20h 2 d 6 d 10 d 15 d l h 5 h 10 h 20h 2 d 6 d 10 d 15 d 5 h 10h 20h 2 d 6 d 10 d 15 d l h 5 h 10 h 20h 2 d 8 d 10 d l h 5 h 10 h 20 h 3 d 8 d 16 d 1.5 h 5 h 7.5 h 24h 1.5 h 5 h 7.5 h 12 h 24 h 1.5 h 5 h 7.5 h 12 h 24 h 1.5 h 5 h 7.5 h 12 h 24 h Amine formed Aniline Sulphanilic acid Sulphanilic acid Sulphanilic acid Sulphanilic acid Naphthionic acid Naphthionic acid Naphthionic acid Naphthionic acid Molar yield of amine yo 84.7 59.6 52.1 45.7 40.1 34.7 18.6 0 120.4 66.0 58.4 52.2 44.9 34.9 18.9 0 67.3 58.3 51.4 44.9 34.8 18.6 0 62.1 37.9 34.8 29.3 17.6 9.7 0 86.7 59.8 51.2 47.6 43.4 25.5 0 26.3 3.7 1.4 0 25.9 3.6 1.2 0 0 24.8 3.3 1.4 0 0 25.6 3.8 1.0 0 0 Molar yield of ammonia % 145 148 155 160 168 182 196 90 137 141 147 153 166 181 196 138 148 149 163 158 181 196 140 158 162 176 24 1 363 402 110 141 145 151 157 173 198 183 199 199 201 184 200 205 206 207 186 199 203 203 204 182 199 201 22 1 399 700 FOGG AND SUMMAN groups gives a yield of 200%.No results have been given in Table V for Yellow 2G due to the good light stability of this food colour (see Table 111); the eventual yield of ammonia was confirmed as being 200%. Discussion This study has provided information on the enhanced degradation of food colouring matters and ascorbic acid in the presence of each other during light degradation. The formation of aniline sulphanilic acid and naphthionic acid during these degradations has been demonstrated and their concentrations have been determined spectrophotometrically.These simple amines have been shown to degrade further to give ammonia. Naphthionic acid in particular degrades rapidly in this way even in the absence of ascorbic acid although the degradation is even more rapid in its presence. Sulphanilic acid gives appreciable amounts of ammonia within a few hours in strong light in the presence of ascorbic acid, whereas ammonia is observed only after several days in the absence of ascorbic acid. Aniline is much stabler than is sulphanilic acid. Quantitative yields of ammonia are obtained in all instances indicating that both nitrogen atoms in the azo linkages are converted into ammonia eventually. With Red 2G and Black PN additional ammonia might have been expected from photolysis of the acetamido groups in these molecules but this was not observed.Brown FK gave a yield corresponding to the formation of two ammonia molecules per molecule; as Brown FK is reported to be a mixture of compounds containing 1-3 azo groups and additional amino groups a higher yield than this might have been expected. The light degradation technique might serve as a useful means of assessing samples of Brown FK. Details of a high-performance liquid chromatographic (HPLC) study of the light and heat degradation of food colours will be reported elsewhere.* Studies similar to those reported here are also being made of the heat degradation (130 “C in sealed vials) of food colours in the presence and absence of vitamin C.Preliminary results indicate that simple amines and ammonia are formed but in much lower yields than in the light degradation studies. Phenols are the likely products of the degradation of the amines in light but further HPLC studies will be required in order to confirm this. Degradation in this study was carried out in fairly intense light. The purpose of using these accelerated degradation conditions was to make the identification of products easier. When a complete list of products is obtained it will still be necessary to show that these are formed under less extreme and more normal food processing and storage conditions and to study the extent to which any of them are formed. It should be noted that the pH at which these studies were carried out (5.5) was chosen as being convenient for the polarographic determination of ascorbic acid. Addition of EDTA was made so that the reaction of ascorbic acid with dissolved molecular oxygen which is extremely rapid could be disregarded. Clearly EDTA is not normally present in foodstuffs. Further soft drinks normally have a pH of 2.5-3 and other additives such as preservatives, antioxidants and sugars may also have significant effects on the stability of the food colours. The authors thank Pointing Limited and Williams (Hounslow) Limited for providing samples of food colouring matters and the latter for useful comments Dr. N. T. Crosby (Laboratory of the Government Chemist) and Mr. B. A. Saturley (Beecham Products) for helpful advice and the Government of Saudi Arabia for financial support for A.M.S. References 1. 2. 3. 4. 5. 6. 7. 8. 9. Fogg A. G and Yoo K. S. Analyst 1979 104 723. Fogg A. G. and Yoo K. S. Analyst 1979 104 1087. Fogg A. G. and Whetstone M. R. Analyst 1982 107 455. Fogg A. G. and Whetstone M. R. to be published. Fogg A. G. and Bhanot D. Analyst 1980 105 234. Fogg A. G. and Bhanot D. Analyst 1980 105 868. Fogg A. G. and Bhanot D. Analyst 1981 106 883. “Report of the Food Additives and Contaminants Committee Interim Report on the Review of Norwitz G. and Kellher P. N. Anal. Chem. 1981 53 1238. Received July 27th 1982 Accepted August 23vd 1982 Colouring Matter in Food Regulations 1973,” H.M. Stationery Office London 1979