三乙胺辅助镁沉淀-真空萃取-波长扫描光腔衰荡光谱法测定高盐水中氢和氧同位素组成

Triethylamine-assisted Mg(OH)_(2) precipitation and vacuum extraction of high-salinity water for the determination of oxygen and hydrogen isotopic compositions using cavity ring-down spectroscopy

本研究采用三乙胺辅助镁沉淀去除样品里的镁离子;真空萃取水样后,采用波长扫描光腔衰荡光谱法(WS-CRDS)测定,建立了精确测定高盐水样中氢和氧同位素(δ^(18)O和δ^(2)H)的方法。结果表明,样品里加入2%的三乙胺辅助镁沉淀,导致氧同位素分馏在±0.1‰以内,氢同位素分馏在±0.3‰以内,说明在仪器的分析精度范围内三乙胺辅助镁沉淀是可行的。样品用量及沉淀时间对镁的去除率影响不大,实验选择样品用量为10 mL,沉淀1 h。在优化的实验条件下,对实际高盐水样和标准海水样品IAPSO进行了测定,同时采用热转换元素分析-气体稳定同位素比质谱法(TC/EA-IRMS)进行验证,2个方法的测定结果具有一致性。该脱盐方法处理过程简单,克服了高盐水样品中溶解盐对氢和氧同位素测试的影响,适用于对各种类型和来源的高盐溶液进行氢和氧同位素分析。

In this study,a high-precision method for the determination of hydrogen and oxygen isotopes in high-salinity water was established.The method used triethylamine-assisted Mg(OH)_(2) precipitation and vacuum extraction of high-salinity water,followed by measuring δ^(18)O and δ^(2)H using wavelength scanning cavity ring-down spectroscopy(WS-CRDS).According to the results,the addition of 2%triethylamine-assisted Mg(OH)_(2) precipitation caused a fractional difference in isotopes within±0.1‰for oxygen and within±0.3‰for hydrogen.This difference was negligible as it falls within the analytical accuracy range of the instrument,indicating that triethylamine-assisted Mg^(2+)precipitation is feasible.The removal rate of Mg(OH)_(2) was not significantly affected by the sample dosage or precipitation time.The sample dosage used was 10 mL and the precipitation time was 1h.Under the optimized procedure,the isotopic compositions of three high-salinity samples and an IAPSO standard seawater for comparison were determined by using the proposed method and thermal conversion/elemental analyzer-isotope ratio mass spectrometry(TC/EA-IRMS),respectively.The results for δ^(18)O and δ^(2)H obtained from both methods were consistent.The method is feasible and simple,allowing for rapid extraction of many samples regardless of salt type or origin,fully overcoming isotope salt effects.