Quantitative Estimation of Pentose When pentoses are heated with conc. HCl , furfural is formed which condenses with orcinol in the presence of ferric ions to give a blue-green color.

* Principle ∆ + HCl Furfural Pentose

* Principle Fe+3 + Blue Green Complex Furfural Orcinol

Materials 1. Orcinol reagent (0.2% in conc. H2SO4 ). 2. Ribose 2mg/ml (0.2%) in water. 3. Colorimeter or spectrophotometer.

Boiling Water Bath Mix Well Read the Optical Density at 665 nm Tube # Blank St. unk. 25 min. 60 30 15 45 5 10 20 25 35 40 50 55 Boiling Water Bath Orcinol (ml) 7.5 7.5 7.5 Pentose (ml) 0 2.5 2.5 D.W (ml) 2.5 0 0 Mix Well COOL to Room Temperature in cold water Read the Optical Density at 665 nm

* Calculations CUn. = A Un. × C St. Absorbance of Unknown Absorbance of Standard = Concentration of Unknown Concentration of Standard CUn. = A Un. × C St. A St. Samar A. Damiati