Guan Chengguo, Peng Yongbo, Wei Ziran, Gong Shanggui, Bao Huiming
State Key Laboratory of Palaeobiology and Stratigraphy, Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences, Nanjing, China.
International Center for Isotope Effects Research, Nanjing University, Nanjing, China.
Rapid Commun Mass Spectrom. 2023 Sep 30;37(18):e9601. doi: 10.1002/rcm.9601.
The oxygen isotope composition of phosphate (δ O ) is widely employed for reconstructing paleotemperature and tracing biogeochemical phosphorus cycling. However, existing phosphate purification protocols do not work well for igneous rocks and igneous weathering profiles (IWPs). A reliable purification method is needed for measuring δ O in these materials.
Our phosphate purification method includes two steps of cation exchange resin treatment separated by a step of calcium phosphate precipitation (R-Ca-R method). In addition, the silver phosphate precipitation in our procedure is featured by slow evaporation to crystallization until the appearance of ammonium nitrate or silver nitrate crystals. We evaluated our methods on weathered and pristine igneous rocks, phosphorite rocks, KH PO , and (NH ) HPO solutions.
Our purification method converted over 99.9% phosphate in solution to calcium phosphate, which can be easily decalcified by cation resin. The improved silver phosphate precipitation method produced high phosphate yields (97.1%-99.5%) and retained original δ O within analytical uncertainty (2σ = 0.6‰). We applied the purification and precipitation method on five igneous rocks and IWPs, and obtained δ O values ranging from 6.4‰ to 8.0‰. Duplicate phosphate extractions yielded δ O values differing by less than 0.3‰.
We developed a new phosphate purification method that is applicable to phosphate extraction in igneous rocks and IWPs. We also proposed a reliable indicator for the termination of silver phosphate precipitation. Our method can achieve high phosphate yield and reproducible δ O value.
磷酸盐的氧同位素组成（δ¹⁸O）被广泛用于重建古温度和追踪生物地球化学磷循环。然而，现有的磷酸盐纯化方案对火成岩和火成岩风化剖面（IWPs）效果不佳。需要一种可靠的纯化方法来测量这些材料中的δ¹⁸O。
我们的磷酸盐纯化方法包括两步阳离子交换树脂处理，中间隔着一步磷酸钙沉淀（R-Ca-R法）。此外，我们方法中的磷酸银沉淀的特点是缓慢蒸发至结晶，直到出现硝酸铵或硝酸银晶体。我们在风化和原始火成岩、磷块岩、KH₂PO₄和(NH₄)₂HPO₄溶液上评估了我们的方法。
我们的纯化方法将溶液中超过99.9%的磷酸盐转化为磷酸钙，磷酸钙可通过阳离子树脂轻松脱钙。改进后的磷酸银沉淀法产生了高磷酸盐产率（97.1%-99.5%），并在分析不确定度（2σ = 0.6‰）内保留了原始的δ¹⁸O。我们将纯化和沉淀方法应用于五种火成岩和IWPs，获得的δ¹⁸O值范围为6.4‰至8.0‰。重复的磷酸盐提取产生的δ¹⁸O值差异小于0.3‰。
我们开发了一种新的磷酸盐纯化方法，适用于火成岩和IWPs中的磷酸盐提取。我们还提出了一个可靠的磷酸银沉淀终止指标。我们的方法可以实现高磷酸盐产率和可重复的δ¹⁸O值。
