Modified method of separation and purification of U, Th in coral sample with UTEVA resin
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摘要: 珊瑚是记录海洋环境变化信息的载体之一，测定其U/Ca比值可重建海水温度或测定Th/U同位素比值可计算年龄重建海平面高度等。准确测定珊瑚中U、Th含量及同位素比值是提取所记载的海洋环境变化信息的前提，其难点在于高Ca基体分离和痕量U、Th富集纯化。基于此，本研究拟采用UTEVA树脂改进了一步富集分离珊瑚中U、Th的前处理方法，并联合高分辨电感耦合等离子体质谱仪测定U、Th含量。结果证明：上样介质HNO3浓度由3 mol/L降至2 mol/L不影响U、Th的吸附效率，用2 mL Milli-Q水可将U完全洗脱，U、Th的全流程空白值（mean±1σ, n =12）分别为（1.32±0.65） pg、（2.05±0.63）pg，显著降低了U的全流程空白值。测定了3个海南滨珊瑚中U含量（mean±1σ，n=6），分别为（3.46±0.02 ）μg/g、（2.67±0.05）μg/g、（2.15±0.07）μg/g，Th含量（mean±1σ，n=6）分别为（10.12±0.24）ng/g、（4.82±0.10）ng/g、（5.62±0.12）ng/g，测定精度均在3.3%以内，U、Th加标回收率分别为97.9%～100.9%、97.3%～99.7%，方法准确度高，精密度好。本研究可为测定珊瑚等碳酸盐类样品中U、Th含量及其同位素提供准确、简便和快速的样品前处理方法。
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关键词:
- 珊瑚 /
- 铀 /
- 钍 /
- UTEVA树脂 /
- 电感耦合等离子体质谱法
Abstract: Corals are one of the carriers for recording information about changes in the marine environment. For example, determining U/Ca to reconstruction of sea water temperature or measure the Th/U isotopic ratio for dating to reconstruction sea level etc. However, measuring the U and Th contents and isotopic ratio of corals is a prerequisite for extracting the recorded marine environmental change information, the difficulty lies in the separation of Ca matrix and enrichment and purification of trace U and Th. Based on this, this study modified the pretreatment method of separation and purification U and Th with single column stage of UTEVA resin, and then combined with high resolution inductively coupled plasma mass spectrometry to determine U and Th contents of corals. The results demonstrate that the HNO3 medium concentration decrease from 3 mol/L to 2 mol/L will not affect the absorption efficiency of U and Th; 2 mL Milli-Q water can completely elute U, which significantly reduces the procedure blank value of the entire process of U; the improved method is used to determine the U and Th contents of three Hainan littoral corals (n=6, 1σ): U are (3.46±0.02)μg/g, (2.67±0.05)μg/g, (2.15±0.07)μg/g, respectively, Th are (10.12±0.24)ng/g, (4.82±0.10)ng/g, (5.65±0.12)ng/g, respectively; and the determination accuracy is below 3.3%, recovery rate of standard addition of U, Th are 97.9%–100.9%, 97.3%–99.7%, respectively. The method has high accuracy and good precision. This study provides a more accurate, convenient and rapid experimental method for the analysis of U and Th content and isotopic ratio in corals and other carbonate samples.-
Key words:
- coral /
- U /
- Th /
- UTEVA resin /
- inductively coupled plasma mass spectrometry (ICP–MS)
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图 1 珊瑚样品中U、Th分离纯化流程
Fig. 1 The flow of U, Th separation and purification in coral sample
图 2 HNO3浓度对U、Th吸附效率的影响
Fig. 2 The effect of HNO3 concentration on U, Th absorption efficiency
图 3 HCl浓度对U、Th洗脱效率的影响
Fig. 3 The effect of HCl concentration on the U, Th elution efficiency
表 1 不同浓度HNO3、HCl介质中U和Th在UTEVA树脂上的吸附系数
Tab. 1 Absorption coefficient of U and Th on UTEVA resin with different concentrations of HNO3 and HCl
HNO3浓度/
（mol·L−1）吸附系数 HCl浓度/
（mol·L−1）吸附系数 KdTh KdU KdTh KdU 1.0 28 60 0.5 − 0.9 2.0 50 120 1.0 5×10−2 1 3.0 70 200 2.0 8×10−2 6 4.0 120 230 2.5 10×10−2 15 5.0 170 290 3.0 11×10−2 20 6.0 180 295 4.0 16×10−2 60 7.0 200 300 5.0 30×10−2 100 注：表中U、Th吸附系数参考文献[21]的吸附系数变化趋势图；−代表0.5 mol/L HCl介质下Th吸附系数没有具体数值。 
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表 2 实验器材
Tab. 2 Experimental equipment
器材名称 规格/型号 生产厂家 电感耦合等离子体质谱仪 Element 2 德国Thermo Electron公司 PFA微型柱 15 mL 南京滨正红公司 PFA溶样杯 6 mL 南京滨正红公司 痕量元素分离纯化Teflon工作台 / 自主设计[26] Teflon电热板 定制 南京滨正红公司 FEP瓶 60 mL、500 mL 美国Thermo公司 LDPE瓶 15 mL、30 mL、
60 mL、125 mL美国Thermo公司 PFA对瓶酸平衡装置 / 美国Savillex公司 石英亚沸蒸馏器 / 金坛晶玻实验仪器厂 高型烧杯 1 L 环球公司 移液器 100 μL、1 mL 美国Thermo公司 电子天平 精确至0.000 01g 德国Sartorius公司
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表 3 实验试剂
Tab. 3 Experimental reagent
试剂名称 级别/浓度 生产厂家 HNO3 高纯 自主提纯 HCl 高纯 自主提纯 HF >99.999% 美国Sigma公司 HClO4 >99.999% 美国Sigma公司 H2O2 优级纯 国药化学试剂公司 CaCO3 ≥99.999% 美国Sigma公司 Ca标准溶液 1 000 μg/mL (5% HNO3) 美国J. T. Baker公司 Mg标准溶液 1 000 μg/mL (5% HNO3) 美国J. T. Baker公司 Sr标准溶液 1 000 μg/mL (2% HNO3) 美国J. T. Baker公司 Sc标准溶液 1 000 μg/mL (2% HNO3) 美国Spex公司 Tl标准溶液 1 000 μg/mL (2% HNO3) 美国Spex公司 Th标准溶液 1 000 μg/mL (2% HNO3) 美国Spex公司 U标准溶液 1 000 μg/mL (2% HNO3) 美国Spex公司 Milli-Q水 18.2 MΩ·cm 美国Millipore公司 UTEVA树脂 分析级 (50~100 μm、
100~150 μm)法国TRISKEM International公司 注：MΩ·cm为Milli-Q水电阻率单位。
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表 4 Element 2最佳工作参数
Tab. 4 Optimized operational parameters of Element 2
仪器运行参数 数据获取参数 射频功率/W 1 200 质量窗口/% 15 分辨率/(M·△M−1) 300 扫描步长 100 辅助气流量/(L·min−1) 1.000 积分时间/s 232Th: 0.100,
238U: 0.100,
205 Tl: 0.050样品气流量/(L·min−1) 约1.12 积分窗口/% 15 样品提取流速/(μL·min−1) 约50 检测模式 Counting 扫描类型 Escan 扫描次数 3×4 注：M/△M为质谱仪中分辨率的单位。
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表 5 不同粒径的UTEVA对U、Th的分离效果
Tab. 5 Different particle size of UTEVA resin on U, Th separation efficiency
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表 7 U、Th回收率与相对标准误差
Tab. 7 U, Th recovery and relative standard error
元素 日期 测定值/ng 平均值/ ng (mean±1σ, n=11) 相对标
准误差/%
（n=11）平均回
收率/%
(n=11)Th 2021年4月12日 0.544±0.012
(n=3, 1σ)0.554±0.016 3.0 92.3 2021年4月22日 0.566±0.019
(n=4, 1σ)2021年4月26日 0.549±0.011 (n=4, 1σ) U 2021年4月12日 94.7±2.00
(n=3, 1σ)95.5±1.6 1.7 95.5 2021年4月22日 96.5±1.42
(n=4, 1σ)2021年4月26日 95.3±1.33
(n=4, 1σ)
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表 8 海南滨珊瑚样品中U、Th含量
Tab. 8 U, Th contents in Hainan coral samples
样品编号 元素 取样量/
mg称取样品测定值/ng
(mean±1σ, n=6)精度
/%珊瑚中含量/(μg·g−1)
(mean±1σ, n=6)标准加入量/
ng加标后测定值/ng
(mean±1σ, n=6)加标回收率/%
(mean±1σ, n=6)Coral-1 Th 50 0.506±0.012 2.0 (10.12±0.24)×10−3 0.500 0.992±0.023 98.6±2.2 U 50 172.9±1.1 0.6 3.46±0.02 150.0 325.8±4.8 100.9±1.5 Coral-2 Th 50 0.241±0.005 2.1 (4.82±0.10)×10−3 0.500 0.739±0.021 99.7±1.0 U 50 133.4±2.2 1.7 2.67±0.05 150.0 277.4±1.9 97.9±1.0 Coral-3 Th 50 0.281±0.006 1.8 (5.62±0.12)×10−3 0.500 0.760±0.017 97.3±2.3 U 50 107.2±3.6 3.3 2.15±0.07 150.0 255.2±1.2 99.2±0.5
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