title: Extractability of water-soluble soil organic matter as monitored by spectroscopic and chromatographic analyses.
abstract: OBJECTIVE
  Cold and hot water processes have been intensively used to recover soil organic matter, but the effect of extraction conditions on the composition of the extracts were not well investigated. Our objective was to optimize the extraction conditions (time and temperature) to increase the extracted carbon efficiency while minimizing the possible alteration of water extractable organic matter of soil (WEOM).
  
  
  METHODS
  WEOM were extracted at 20°C, 60°C, or 80°C for 24 h, 10-60 min, and 20 min, respectively. The different processes were compared in terms of pH of suspensions, yield of organic carbon, spectroscopic properties (ultraviolet-visible absorption and fluorescence), and by chromatographic analyses.
  
  
  RESULTS
  For extraction at 60°C, the time 30 min was optimal in terms of yield of organic carbon extracted and concentration of absorbing and fluorescent species. The comparison of WEOM 20°C, 24 h; 60°C, 30 min; and 80°C, 20 min highlighted significant differences. The content of total organic carbon, the value of specific ultraviolet absorbance (SUVA(254)), the absorbance ratio at 254 and 365 nm (E (2)/E (3)), and the humification index varied in the order: WEOM (20°C, 24 h) < WEOM (80°C, 20 min) < WEOM (60°C, 30 min). The three WEOM contained common fluorophores associated with simple aromatic structures and/or fulvic-like and common peaks of distinct polarity as detected by ultra performance liquid chromatography.
  
  
  CONCLUSIONS
  For the soil chosen, extraction at 60°C for 30 min is the best procedure for enrichment in organic chemicals and minimal alteration of the organic matter.
authors.affiliation: Laboratoire de Photochimie Moléculaire et Macromoléculaire (LPMM), Clermont Université, Université Blaise Pascal, BP 10448, 63000 Clermont-Ferrand, France.
authors.forename: Ezzhora
authors.initials: E
authors.lastname: Nkhili
authors.forename: Ghislain
authors.initials: G
authors.lastname: Guyot
authors.forename: Nathalie
authors.initials: N
authors.lastname: Vassal
authors.forename: Claire
authors.initials: C
authors.lastname: Richard
mesh_terms: D002853:Chromatography, Liquid / Q000379:methods; D004784:Environmental Monitoring / Q000379:methods*; D006863:Hydrogen-Ion Concentration; D056951:Photoelectron Spectroscopy; D012987:Soil / Q000032:analysis; D012989:Soil Pollutants / Q000032:analysis / Q000302:isolation & purification*; D012995:Solubility; D013050:Spectrometry, Fluorescence; D014867:Water
chemical_list: D012987:Soil; D012989:Soil Pollutants; D014867:Water