Determination of Rare Earth Elements in Sepiolite by ICP-MS Using Microwave Digestion
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摘要: 海泡石是一种纤维状含水的富镁硅酸盐黏土矿，其中的稀土元素含量在1×10-7~1×10-5之间，目前还没有建立海泡石中稀土元素的国家标准分析方法。测定岩石中的稀土元素主要是采用电感耦合等离子体质谱法（ICP-MS），样品前处理一般采用封闭溶矿和碱熔，但这两种处理方法耗时较长，效率不高。本文通过比较硝酸-氢氟酸-过氧化氢、硝酸-氢氟酸、硝酸-过氧化氢三种样品前处理方法，确定使用硝酸-氢氟酸溶矿，然后进行微波消解同时赶去氢氟酸，避免氢氟酸与稀土元素生成难溶的氟化物，再采用ICP-MS法测定15种稀土元素的含量。由于海泡石中的镁含量较高，为降低基体效应，以103Rh和185Re作内标补偿基体效应和校正灵敏度漂移，各元素测定值的准确性显著提高，回收率为91.2%~110.9%，检出限为0.002~0.011 μg/L，精密度≤ 2.79%。本方法与封闭酸溶ICP-MS法的分析结果吻合较好，且用酸量少（7 mL），溶矿效率高（1 h），检出限更低。
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关键词:
- 海泡石 /
- 稀土元素 /
- 微波消解 /
- 硝酸-氢氟酸 /
- 电感耦合等离子体质谱法
Abstract:BACKGROUNDSepiolite is a fibrous hydrous magnesium rich silicate clay mineral with the content of rare earth elements between 1×10-7 and 1×10-5. There is no national standard method for the determination of rare earth elements in sepiolite. Determination of rare earth elements in rocks commonly uses ICP-MS. Sample pretreatments generally use closed digestion and alkaline fusion, but these two treatments are time consuming and inefficient. OBJECTIVESTo find an efficient dissolution method for the determination of 15 rare earth elements in sepiolite. METHODSBy comparing three sample pretreatment methods of nitrate hydrofluoric acid hydrogen peroxide, nitric acid-hydrofluoric acid and nitric-acid hydrogen peroxide, the nitric acid-hydrofluoric acid solution system was selected. Microwave digestion was carried out and the hydrofluoric acid was driven off to avoid the formation of insoluble fluorides from the hydrofluoric acid. The content of 15 rare earth elements was determined by ICP-MS. RESULTSDue to the high content of magnesium in sepiolite, two internal standards of 103Rh and 185Re are selected to compensate for the drift of analytical signals and to correct matrix effects. The recoveries of the method range from 91.2% to 110.9%. The detection limits are 0.002-0.011 μg/L, and the precisions are 0.81%-2.79%. CONCLUSIONSThe result of this method is in good agreement with that of the closed acid-digestion ICP-MS method, and with a small amount of acid (7 mL), high digestion efficiency (1 h), and a lower detection limit. -
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表 1 微波消解程序
Table 1. Program of microwave digestion
实验条件 1 2 3 4 目标温度(℃) 100 150 200 100 升温时间(min) 5 3 3 1 保温时间(min) 2 10 20 10 
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表 2 不同溶矿体系下元素的分析结果
Table 2. Analytical results of elements in sample pretreated with different acid digestion conditions
稀土元素 稀土元素测定值(μg/g) 硝酸-氢氟酸-过氧化氢 硝酸-氢氟酸 硝酸-过氧化氢 89Y 21.3 21.6 12.5 139La 33.1 32.4 11.8 140Ce 53.4 52.7 22.6 141Pr 6.32 6.41 3.12 146Nd 24.5 25.0 9.13 147Sm 4.31 4.45 2.16 151Eu 0.86 0.84 0.52 157Gd 4.27 4.31 1.87 159Tb 0.66 0.64 0.39 163Dy 3.27 3.25 1.78 165Ho 0.64 0.61 0.38 166Er 1.75 1.72 1.09 169Tm 0.21 0.24 0.13 172Yb 1.49 1.55 0.96 175Lu 0.21 0.23 0.11
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表 3 未赶氢氟酸与赶氢氟酸测定结果比较
Table 3. Comparison of analytical results of elements in hydrofluoric acid-driving and hydrofluoric acid-keeping samples
稀土元素 测定值(μg/g) 赶酸 未赶酸 相对偏差(%) 89Y 21.6 2.31 89.3 139La 32.4 2.98 90.8 140Ce 52.7 38.6 26.8 141Pr 6.41 1.22 80.9 146Nd 25.0 3.25 87.0 147Sm 4.45 1.11 75.1 151Eu 0.84 0.28 66.7 157Gd 4.31 1.16 73.1 159Tb 0.64 0.15 76.6 163Dy 3.25 1.39 57.2 165Ho 0.61 0.18 70.5 166Er 1.72 0.36 79.1 169Tm 0.24 0.04 83.3 172Yb 1.55 0.33 78.7 175Lu 0.23 0.06 73.9 注：相对偏差=(未赶酸测定值-赶酸测定值)/赶酸测定值×100%。
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表 4 方法检出限和精密度
Table 4. Detection limit and precision tests of the method
稀土元素 内标 方法检出限(μg/L) 方法精密度 测定值(μg/g) RSD(%) 89Y 103Rh 0.006 21.6 1.16 139La 103Rh 0.005 32.4 2.15 140Ce 103Rh 0.007 52.7 1.23 141Pr 103Rh 0.002 6.41 2.18 146Nd 103Rh 0.003 25.0 0.89 147Sm 103Rh 0.002 4.45 1.36 151Eu 103Rh 0.008 0.84 2.58 157Gd 185Re 0.011 4.31 1.62 159Tb 185Re 0.004 0.64 2.34 163Dy 185Re 0.002 3.25 0.81 165Ho 185Re 0.003 0.61 2.38 166Er 185Re 0.002 1.72 2.15 169Tm 185Re 0.002 0.24 2.79 172Yb 185Re 0.002 1.55 1.89 175Lu 185Re 0.003 0.23 2.31
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表 5 方法准确度
Table 5. Accuracy tests of the method
稀土元素 测定值(μg/g) 回收率(%) 样品含量 加标量 样品加标后 89Y 21.6 30 50.5 97.9 139La 32.4 30 60.8 97.4 140Ce 52.7 30 78.3 94.7 141Pr 6.41 5 11.6 101.7 146Nd 25.0 30 50.2 91.2 147Sm 4.45 5 9.87 104.4 151Eu 0.84 1.0 2.04 110.9 157Gd 4.31 5 9.15 98.3 159Tb 0.64 1.0 1.76 107.3 163Dy 3.25 5.0 8.38 101.6 165Ho 0.61 1.0 1.66 103.1 166Er 1.72 1.0 2.82 103.7 169Tm 0.24 1.0 1.21 97.6 172Yb 1.55 1.0 2.41 94.5 175Lu 0.23 1.0 1.24 100.8
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表 6 两种方法分析结果对比
Table 6. Comparison of the two methods
稀土元素 测定值(μg/g) 相对偏差(%) 微波消解法 封闭酸溶法 89Y 21.6 20.8 3.70 139La 32.4 33.9 4.63 140Ce 52.7 54.5 3.42 141Pr 6.41 6.38 0.47 146Nd 25.0 26.7 6.80 147Sm 4.45 4.62 3.82 151Eu 0.84 0.89 5.95 157Gd 4.31 4.36 1.16 159Tb 0.64 0.58 9.38 163Dy 3.25 3.46 6.46 165Ho 0.61 0.63 3.28 166Er 1.72 1.76 2.33 169Tm 0.24 0.25 4.17 172Yb 1.55 1.38 9.68 175Lu 0.23 0.21 8.70
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