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. Reductive 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 ; difleerential-pulse polarography 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 1 1 and adjust to pH 5.5 with 1 M sodium hydroxide solution.
Ascorbic acid -E D T A 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.* 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.
A new, efficient, and sensitive cloud point methodology was developed for preconcentration of trace quantities of cobalt and nickel in water and food samples.
Ascorbic acid can be determined by flow injection amperometry at a sessile mercury drop electrode without the need to deoxygenate the eluent or sample. The determination is made at +0.19 V vs. S.C.E. in pH 5.5 acetate buffer. The size of the blank signal is equivalent to about 0.01 pg ml-1 of ascorbic acid and the signal is rectilinear up to about 60 pg ml-1. Chloride gives an oxidation signal at the mercury electrode but at a more positive potential and at the 1 1-19 ml-1 level of ascorbic acid 1000 pg ml-1 of chloride ion did not interfere.Hydrodynamic voltammograms of dopamine [2-(3,4-dihydroxyphenyl)ethylaminel show a plateau distinct from that of ascorbic acid and the mercury oxidation cut-off. Calibration graphs obtained at +0.26 V vs. S.C.E. for dopamine are rectilinear in the range 0.1-60 pg ml-1. At +0.26 V chloride ion gives a signal approximately 1% of that of dopamine on a molar basis and interferes at higher ratios.
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