I am looking for a simple way to distinguish between glucose and fructose samples. Currently, I am doing that by melting temperature method. Can anybody suggest me some easy way to do that?
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1$\begingroup$ Related: Why does fructose reduce Tollen's reagent and Fehling's solution? $\endgroup$– user7951Commented Aug 15, 2016 at 10:58
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4 Answers
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One of the simplest ways would be bromine-water test. Bromine water oxidizes glucose to gluconic acid, hence decolorize the solution. Being a mild oxidizing agent, Bromine water is not capable of oxidizing fructose (ketone).
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Go for Seliwanoff's Test. It is based on the simple fact that when heated, ketose sugars are more rapidly dehydrated than aldoses. After acidic hydrolysis of both, we add a pinch of resorcinol(0.5%) and concentrated HCl(3N). Fructose reacts to give a deep red cherry colour whereas Glucose reacts slightly to produce a faint pink colour.
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$\begingroup$ Why are ketoses more easily dehydrated than aldoses? $\endgroup$ Commented Jan 21 at 11:17
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Taste tests also work. Fructose is about 2.3 times sweeter tasting than glucose, and the tongue is a very good sweet-sensor.
(source: wikipedia)
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7$\begingroup$ While this is accurate, normally one does not recommend tasting chemicals in a laboratory. $\endgroup$ Commented Aug 15, 2016 at 19:43
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Go for Osazone test.... add phenylhetrazine +sodium acetate + acetic acid...if yellow precipitate appears within two minutes of boiling in waterbath (needle shape crystals)then the sample is Fructose.. if yellow precipitate appears between 5 to 10 minutes of boiling in waterbath (broom shaped crystals)its glucose.