ABSTRACT
Analytical technique on oxygen isotope composition of phosphate in soil has important applications in biogeochemical research. As the composition of the soil is complex with multiple oxygen sources, a liable phosphate enrichment and purification technology is important for phosphate oxygen isotope research. Here we presented a protocol on the analysis of the δ18 Op of inorganic phosphate in soil, and phosphate was purified with multiple mineral precipitations and finally precipitated as silver phosphate. The efficiency of NH4 OH purification method was examined and the purity of the product was verified through XRD and element analysis. The result showed that treatment of the Ag3 PO4 sample by recrystallizing with ammonia could remove the impurity efficiently without significantly modifying oxygen isotope compositions. The validity of sample processing and reliability of isotope analyses were confirmed by processing a KH2 PO4 standard in parallel with soil P sample. The analytical result of three soil types indicated that this method provided good precision of 0. 2‰. The differences of δ18 Op between three soils groups are significant ( From 15. 2‰ to 19. 5‰) and can be used to tracing P sources.
ABSTRACT
Soil water is one of the most important components in hydrological cycle. The stable hydrogen and oxygen isotopes in soil water have been increasingly used in the ecological, environment and hydrological research. In view of different techniques for extracting soil water, there is significant difference in theδD andδ18 O composition. This paper presents a method for analyzing hydrogen and oxygen isotopes in soil water by using elemental analyzer and isotope ratio mass spectrometry with accelerated solvent extraction for sample pretreatment. The conditions are: extraction solvent: dichloromethane, temperature: 100 ℃, pressure of 10. 3 MPa, static time:10 min. The samples were extracted three times, and with cycle values of four, four and three, respectively. Comparing with the added water, the deuterium and oxygen isotope values in the extracted soil water enrich 2. 12‰-4. 58‰ and 0. 17‰-0. 93‰, respectively. The reproducibility of replicate extractions of soil water is around ±0. 89‰ for δD and ±0. 37‰ for δ18 O.