Direct determination of allophane and imogolite in Andosols using nuclear magnetic resonance spectroscopy

Allophane and imogolite are the major weathering products of volcanic materials at early stage of the soil formation processes of Andosols. In general, the amounts of allophane plus imogolite in soils are determined by a selective dissolution methods using acid-oxalate, although the accuracy of the indirect method is not well understood. In the present study, the amounts of allophane plus imogolite in Andosol profiles were determined directly by using solid-state 29 Si nuclear magnetic resonance (NMR) spectroscopy and compared the results with those by the selective dissolution method. The result suggested that the amounts of allophane plus imogolite determined by the both methods were roughly correlated for many Andosol samples. For soil samples containing large amount of pumice and organic materials, however, it was suggested that the acidoxalate would underestimate and overestimate the amounts of allophane plus imogolite, respectively. Acidoxalate is a convenient and well studied reagent to dissolve allophane and imogolite from soils, but it might not always be reliable depending on the properties of samples. Non-destructive determination by 29 Si NMR