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REVIEW & ANALYSIS

Improved Analytical Techniques for Carbohydrates, Amino Compounds, and Phenols: Tools for Understanding Soil Processes

USDA-ARS, National Soil Tilth Lab., 2110 University Blvd., Ames, IA 50011

^* Corresponding author (dan.olk{at}ars.usda.gov).

A process-level understanding of soil C and N cycling will be facilitated by accurate measurement of biochemical compounds in soil organic matter. This review summarizes some recent developments in analytical procedures for measuring soil carbohydrates, amino compounds (amino acids and amino sugars), and phenols. The emphasis is on methods for soil carbohydrates and amino compounds involving anion chromatography and pulsed amperometry, a sensitive form of detection that has otherwise not been widely used in soil science. This carbohydrate procedure has become a leading method, with high resolution, sensitivity, and reproducibility. The pulsed amperometry analysis for amino compounds may be incrementally better than the conventional approach by HCl extraction, cation exchange chromatography, ninhydrin derivatization, and detection by visible light absorption. The two amino approaches need more rigorous comparison with regard to extraction efficiency and sensitivity for each amino compound. The pulsed amperometry approach also needs evaluation in a wider range of research settings. A recently developed procedure for measuring soil phenols is based on plant biochemistry studies and distinguishes ether-linked phenols (mostly vanillyl and syringyl) from ester-linked phenols (mostly coumaric acid and ferulic acid). Its applications in a limited number of studies linked specific phenols to soil aggregation and C sequestration. It needs calibration with other phenol methods favored by soil scientists and biogeochemists, and it needs to be evaluated in a range of research settings. Like the pulsed amperometry analysis for amino compounds, this distinction of ether- and ester-linked phenols is likely to complement existing techniques. A future goal will be the integration of results from complementary analyses for these biochemical compounds to help us better understand soil processes.

Abbreviations: HPAEC-PAD, high performance anion exchange chromatography and pulsed amperometric detection • HPLC, high performance liquid chromatography • MSA, methanesulfonic acid • NMR, nuclear magnetic resonance • RI, refractive index