Summary:The reactivity of glucose in aqueous alkaline picrate was investigated by spectrophotometry and polarography at 25 °C in 0.51 mol/1 sodium hydroxide. Thin-layer chromatography and infrared spectroscopy studies have conclusively identified the presence of picramic acid in 5:1 and 10:1 glucose picrate test solutions incubated at 25 °C.The polarographic data of an alkaline picrate blank with a concentration of 0.284 mmol/1, show three welldefined nitro group reduction waves with approximate half-wave potentials of -0.62 V, -0.78 V, and -0.93 V and a fourth broad wave appearing near -1.31 V versus a saturated calomel electrode. The addition of glucose to alkaline picrate resulted in a decreased diffusion current for reduction waves 1-3, with little change in reduction wave 4. The reactivity of test solutions containing glucose: picrate in 1:1, 2:1, 5:1 and 10:1 molar ratios was investigated at varied time intervals between 10 and 180 minutes.The absorption spectra of a 10:1 glucose: picrate solution shifted from 356 nm to 375 nm and a broad tailing shoulder absorbance formed in the 450-600 nm region. An orange coloured minor product, separated by thin-layer chromatography, was observed to fluoresce. The maximum excitation and emission wavelengths were 318 nm and 545 nm, respectively. A major, red-coloured product was isolated and identified as picramic acid by infrared spectroscopy. For 10:1 glucose: picrate test solutions incubated at 25 °C, picramic acid formed within 10 minutes. Within the first minute, the colour was observed to change from yellow to orange and then to red.
The effects of ascorbate, the interference of the Jaffé reaction was individually studied by polarography, spectrophotometry, and thin-layer chromatography. Ascorbate was incubated in 28.4 mmol dm−3 picrate blank solution in 0.51 mol dm−3 NaOH at 25.00 ± 0.02 °C and the reactivity of test solution containing ascorbate : picrate was investigated. Picramic acid formed in all ascorbate: 28.4 mmol dm−3 picrate test solutions which explained the observed positive interference of ascorbic acid. No fluorescent product was formed in ascorbate : picrate test solutions. The reactivity of ascorbate : picrate test solutions confirmed that ascorbate was a powerful reducing agent. 2-Furaldehyde which has been listed as one of the degradation products of ascorbic acid, is not identified under the experimental conditions.
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