The purpose of the presence of phenol in the determination of sugars by phenol-sulfuric acid method?
The PRINCIPLE of using phenol in this assay is: In hot acidic medium glucose is dehydrated to hydroxymethyl furfural. This forms a green coloured product with phenol and has absorption maximum at 490 nm. The color for this reaction is stable for several hours, and the accuracy of the method is within ±2% under proper conditions...
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In presence of H2SO4, sugars oxidize to furfural or hydroxymethyl furfural. These products then react with phenol to form a conjugated system with a yellow-gold color. In presence of naphthol, a purple color is produced (Molisch's Test). You can find more in: Chapter Phenol-Sulfuric Acid Method for Total Carbohydrates
In certain cases, different plant tissues develop yellow color after adding sulfuric acid then why there is a need to add Phenol?
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