Improvements in the preparation of phosphate for oxygen isotope analysis from soils and sediments

PLoS One. 2018 Sep 20;13(9):e0204203. doi: 10.1371/journal.pone.0204203. eCollection 2018.

Abstract

In contrast to the successful preparation of phosphate for oxygen isotope analysis from water samples, there are still a series of problems for similar analyses from soils and sediments. Here, we improved and optimized the methods of silver phosphate preparation for oxygen isotope analysis from soils and sediments. During our preparations, organic matter was removed by sodium hypochlorite and XAD-2 resin, while the impurities of elemental silver and its oxide were removed by rapid microprecipitation and ammonium phospho-molybdate and magnesium ammonium phosphate. The total organic carbon and total nitrogen in the prepared silver phosphates from soils and sediments were 0.226±0.033% and 0.030±0.0059% (n = 7), 0.217±0.053% and 0.034±0.0120% (n = 9), respectively, indicating a high removal efficiency of organic matter. We confirmed that adding citric acid during rapid microprecipitation would introduce the impurity of elemental silver, which could be removed by ammonia recrystallization. The pH range of solutions for rapid microprecipitation was optimized at 7.0‒7.5. Results of X-ray Diffraction and stable oxygen isotope analyses showed that the improved method could obtain high pure silver phosphate from soil and sediment samples without oxygen isotope fractionation. This improved procedure provides a foundation for biogeochemical studies on phosphorus in soil and lacustrine environments by using phosphate oxygen isotopes.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Citric Acid / chemistry
  • Environmental Monitoring / methods
  • Geologic Sediments / chemistry*
  • Hydrogen-Ion Concentration
  • Nitrogen / analysis
  • Organic Chemicals / analysis
  • Oxygen Isotopes / analysis*
  • Phosphates / chemistry*
  • Silver Compounds / chemistry*
  • Soil / chemistry*

Substances

  • Organic Chemicals
  • Oxygen Isotopes
  • Phosphates
  • Silver Compounds
  • Soil
  • Citric Acid
  • Nitrogen
  • silver phosphate

Grants and funding

This work was supported by National Natural Science Foundation of China (No. 41476165), the High-level Scientific Research Foundation for the Talents Introduction (J01006033) and Anhui Province Key Laboratory of Wetland Ecosystem Protection and Restoration (Anhui University). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.