Determination of hydrolyzable tannins (gallotannins and ellagitannins) after reaction with potassium iodate.
A widely used method for analyzing hydrolyzable tannins afer reaction with KIO(3) has been modified to include a methanolysis step followed by oxidation with KIO(3). In the new method, hydrolyzable tannins (gallotannins and ellagitannins) are reacted at 85 degrees C for 20 h in methanol/sulfuric acid to quantitatively release methyl gallate. Dried plant samples can be methanolyzed under the same conditions to convert hydrolyzable tannins to methyl gallate. Oxidation of the methyl gallate by KIO(3) at pH 5.5, 30 degrees C, forms a chromophore with lambda(max) 525 nm, which is determined spectrophotometrically. The detection limit of the method is 1.5 microg of methyl gallate, and with plant samples, relative standard deviations of less than 3% were obtained.
Hartzfeld
Paul W
PW
Department of Chemistry and Biochemistry, Miami University, Oxford, Ohio 45056, USA.
Forkner
Rebecca
R
Hunter
Mark D
MD
Hagerman
Ann E
AE
D002851:Chromatography, High Pressure Liquid; D005707:Gallic Acid / Q000031:analogs & derivatives* / Q000032:analysis / Q000737:chemistry; D006868:Hydrolysis; D047348:Hydrolyzable Tannins / Q000032:analysis*; D007452:Iodates / Q000737:chemistry*; D000432:Methanol / Q000737:chemistry; D010084:Oxidation-Reduction; D010945:Plants, Edible / Q000737:chemistry; D017680:Potassium Compounds / Q000737:chemistry*; D013053:Spectrophotometry; D013464:Sulfuric Acids / Q000737:chemistry; D013634:Tannins / Q000032:analysis*
D047348:Hydrolyzable Tannins; D007452:Iodates; D017680:Potassium Compounds; D013464:Sulfuric Acids; D013634:Tannins; C013515:ellagitannin; C052082:methyl gallate; D005707:Gallic Acid; C039693:potassium iodate; C033158:sulfuric acid; D000432:Methanol