Method Study on the Separation and Enrichment of Rhenium Measured by Negative Thermal Ionization Mass Spectrometry
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摘要: Re-Os同位素定年中，丙酮萃取法分离Re比传统的阴离子交换法流程简单快速。用本实验室原有丙酮萃取流程纯化的Re溶液可用电感耦合等离子体质谱(ICP-MS)测定，但由于盐量较高( > 1 mg/mL)不能直接用于负离子热表面电离质谱(N-TIMS)测定。本文对Re-Os同位素定年方法中原有丙酮萃取分离Re的流程进行改进，将丙酮萃取和碱洗时的氢氧化钠浓度由5 mol/L提高到10 mol/L，有效降低了萃取后的Re溶液中的盐量，由此分离纯化的Re溶液经硝酸和过氧化氢处理，可直接点带用于N-TIMS测定。与阴离子交换分离Re方法相比，改进的丙酮萃取方法操作简单，缩减实验时间，同时有效降低全流程空白至3~7 pg，并且1 ng的Re测量信号可达到100 mV以上。经国家一级标准物质(GBW 04436)和实验室铜镍硫化物监控样品(JCBY)验证，利用改进的方法纯化，Re的测定值分别为(17.17±0.50) μg/g和(38.34±0.44) ng/g，与推荐值(17.39±0.32) μg/g和(38.61±0.86) ng/g在不确定度范围内完全吻合。目前改进的丙酮萃取方法已经应用于实际样品分析，并取得了长期稳定的良好效果。
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关键词:
- 铼-锇同位素 /
- 丙酮萃取 /
- 离子交换 /
- 负离子热表面电离质谱法
Abstract: In Re-Os isotope chronology, the acetone extraction process is quicker and easier compared to the anion exchange method. The Re solution which was separated and purified by acetone extraction is suitable for the measurement by Inductively Coupled Plasma-Mass Spectrometry (ICP-MS), but unsuitable for Negative Thermal Ionization Mass Spectrometry (N-TIMS) directly because of high salt contents. An improvement was made to the acetone extraction method to separate and purify Re for N-TIMS determination by increasing the alkalinity concentration from 5 mol/L to 10 mol/L. Compared with the anion exchange method, the acetone extraction process is not only easier to operate with lower blank (Re 3-7 pg), but also saves time. The signal intensity of Re was over 100 mV per 1 ng Re, which met the requirements of a high-accuracy instrument measurement completely. The national first grade standard material of JDC (GBW 04436) and the laboratory reference material of JCBY were measured to verify the improved method. The Re contents of JDC and JCBY obtained from this method were (17.17±0.50) μg/g and (38.34±0.44) ng/g, respectively, which were consistent with the certified value of JDC (17.39±0.32) μg/g and the certified value of JCBY (38.61±0.86) ng/g. The improved procedure was applied to practical samples with good long-term results. -
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表 1 盐残留含量对测量信号强度的影响
Table 1. Effect of the salts on measurement
样品编号 溶液量
V/mL盐量
/mg信号强度
/cps187Re/185Re w(Re)/(ng·g-1) 实测值 不确定度 实测值 不确定度 Re-1 0.5 0.51 46620047 0.56982 0.00093 38.91 0.12 Re-2 1.0 0.92 2525253 0.57228 0.00138 39.18 0.16 Re-3 2.0 1.75 2331002 0.57053 0.00253 38.99 0.28 Re-4 4.0 3.30 874126 0.57379 0.00149 39.34 0.17 注：不确定度包括样品和稀释剂的称量误差、稀释剂的标定误差、质谱测量的分馏校正误差、待分析样品同位素比值测量误差。 
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表 2 不同浓度氢氧化钠介质中丙酮萃取和碱洗后丙酮中夹带氢氧化钠量
Table 2. The amount of NaOH remained in acetone after extraction in different concentration of NaOH solution
NaOH
浓度c/
(mol·L-1)NaOH
体积
V/mL丙酮
体积
V/mL第一次萃取后 NaOH碱洗一次① NaOH
残存量
m/gNaOH
残存率
/%NaOH
残存量
m/gNaOH
残存率
/%2② 10 10 0.58837 73.55 0.05747 7.18 3② 10 10 0.06428 5.36 0.01771 1.48 5② 10 10 0.00265 0.13 0.00165 0.08 10 10 10 0.00017 0.008 注：①萃取时NaOH浓度为2～5 mol/L，用2～5 mol/L的NaOH碱洗一次；NaOH浓度为10 mol/L，用10 mol/L NaOH碱洗一次。 ②数据引自李超等(2009)[15] 。
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表 3 两种分离富集方法对比
Table 3. Comparison of the two methods
JCBY样品
实验编号纯化方式 实际点带
Re总量/ng样品质量/g 185Re信号/
强度V灯丝
温度/℃187Re/185Re w(Re)/(ng(g-1) 实测值 2s 测定值 不确定度① 120918-7-1 丙酮萃取 10 0.50047 0.14017 901 0.62724 0.00035 38.03 0.07 120918-7-2 离子交换 10 0.50047 0.54209 865 0.63424 0.00013 38.73 0.06 120918-8-1 丙酮萃取 10 0.50518 0.08002 883 0.63057 0.00050 38.35 0.08 120918-8-2 离子交换 10 0.50518 0.34121 802 0.63709 0.00031 39.01 0.07 120918-9-1 丙酮萃取 10 0.50194 0.30049 882 0.62798 0.00032 38.41 0.07 120918-9-2 离子交换 10 0.50194 1.44697 864 0.62888 0.00011 38.50 0.06 120918-10-1 丙酮萃取 10 0.50286 0.13744 882 0.63035 0.00034 38.55 0.07 120918-10-2 离子交换 10 0.50286 0.39881 834 0.63192 0.00026 38.71 0.07 丙酮萃取平均值② 38.34 0.44 离子交换平均值② 38.74 0.22 JCBY推荐值 38.61 0.54 注：①不确定度包括样品和稀释剂的称量误差、稀释剂的标定误差、质谱测量的分馏校正误差、待分析样品同位素比值测量误差。
②丙酮萃取平均值和离子交换平均值的不确定度为4个数据的2s。
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表 4 实际样品分析
Table 4. Analytical data of real samples
样品类型 样品实验编号 称样量/g 点带Re
总量/ng185Re信号
强度/V187Re/185Re w(Re)/(ng·g-1) 测定值 不确定度 测定值 不确定度① JDC② 121029-23 0.05001 1 0.11201 0.49456 0.00028 17.04 0.11 121017-23 0.05045 1 0.05381 0.49296 0.00036 17.02 0.11 120924-23 0.05007 1 0.06903 0.49505 0.00031 17.46 0.11 JDC平均值③ 17.17 0.50 JDC推荐值 17.39 0.32 黑色页岩 121009-1 0.40211 1 0.21337 0.17828 0.00012 20.54 0.15 121009-2 0.40165 1 0.48049 0.19125 0.00011 22.18 0.16 121009-3 0.40222 1 0.38583 0.16511 0.00010 17.95 0.13 121009-4 0.40080 1 0.10467 0.22016 0.00032 26.72 0.20 121009-5 0.40095 1 0.58964 0.21671 0.00008 25.88 0.19 121009-6 0.40253 1 0.19951 0.12401 0.00016 12.52 0.09 沥青 121009-9 0.15044 1 0.41827 0.18540 0.00002 46.12 0.33 121009-10 0.12783 1 0.15310 0.17626 0.00003 48.94 0.35 121009-11 0.15072 1 0.57621 0.16337 0.00002 37.72 0.27 黄铜矿 121102-9 1.00866 < 1 0.01940 0.44269 0.00147 9.42 0.08 121102-11 1.00210 < 1 0.21658 0.41944 0.00135 8.30 0.07 121102-12 0.64182 < 1 0.02321 0.31970 0.00134 9.03 0.08 121102-13 1.00382 < 1 0.16849 0.28705 0.00017 4.99 0.04 121102-15 1.00082 < 1 0.09513 0.27758 0.00102 4.77 0.04 玄武岩 121129-6 2.00409 < 0.1 0.04308 0.14310 0.00094 0.02192 0.00025 121129-7 2.00876 < 0.1 0.02626 0.18100 0.00079 0.02919 0.00032 121129-8 2.00869 < 0.1 0.02269 0.18333 0.00113 0.02968 0.00024 121129-9 2.00182 < 0.1 0.01543 0.32034 0.00054 0.06212 0.00047 121129-10 2.00757 < 0.1 0.04454 0.20770 0.00084 0.03535 0.00031 橄榄岩 121129-17 2.00121 < 0.1 0.03529 0.08166 0.00012 0.02641 0.00020 121129-12 3.00267 < 0.1 0.01238 0.50151 0.00840 0.07760 0.00201 121129-14 3.00175 < 0.1 0.04342 1.15430 0.00701 0.42164 0.00885 注： ① 不确定度包括样品和稀释剂的称量误差、稀释剂的标定误差、质谱测量的分馏校正误差、待分析样品同位素比值测量误差；② JDC实测Re含量的单位为μg/g。 ③ JDC平均值的不确定度为3个数据的2s。④ 不同的样品因为Re含量，样品量的多少等不同，所以称样量不一样。例如辉钼矿含量高，可能称0.05 g，黑色页岩称0.4 g，黄铜矿称1 g。个别样品量不够，称样量减少，处理样品时根据沉淀情况适量增减氢氧化钠和丙酮的用量。
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