Ultratrace Gold in High-Purity Graphite by High-Resolution Continuous Light Source Graphite Furnace Atomic Absorption Spectrometry with Hanging Droplet Microextraction
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摘要:
准确测定高纯石墨中的超痕量金，难点是如何在最大程度地减少样品前处理过程中器皿、试剂、材料、环境及设备所引入的二次污染的前提下，实现对样品溶液中超痕量金(0.1 ～1ng/mL)的有效分离和高倍富集。本文建立了铂皿中灰化、酸解、磷酸三丁酯悬滴微萃取的方法用于高纯石墨中超痕量金分析。首先于铂皿中高温灼烧除去样品中的固定碳，然后采用氢氟酸-王水-高氯酸将灰分消解完全制备成样品溶液，再以微升级磷酸三丁酯悬滴作为萃取剂，分离富集样品溶液中的金，最后采用高分辨连续光源石墨炉原子吸收光谱法(GFAAS)对悬滴中的金进行测定。实验结果表明，使用2.5μL磷酸三丁酯悬滴(氯仿体积为20%)作为萃取剂，在10%盐酸介质的样品溶液中萃取金2min，对金的富集倍数可达283倍。在实验条件下，金的质量浓度在0.1～2.0ng/mL范围内与其吸光度呈良好的线性关系，相关系数r为0.999，检出限为0.11ng/g，样品溶液中一定量的共存元素(如钠、镁、铝)对金的测定无干扰。按照实验方法测定5个高纯石墨实际样品中的金含量，测定结果的相对标准偏差(RSD，n=6)为1.5%～4.9%，加标回收率为94.9%～105.3%。
Abstract:The major challenge in accurately determining ultratrace gold in high-purity graphite is how to achieve effective separation and high enrichment of it (0.1−1ng/mL) in the sample solution, while minimizing the secondary pollution introduced by vessels, reagents, materials, environment, and equipment during the sample pretreatment process. A new method for the analysis of ultratrace gold in high-purity graphite is established by ashing and acid dissolution in a platinum dish, followed by microextraction with a hanging droplet of tributyl phosphate. Firstly, the fixed carbon in the sample was removed by high-temperature burning in a platinum vessel; then, the ash was completely dissolved into a sample solution using hydrofluoric acid-aqua regia-perchloric acid; next, micro-upgraded tributyl phosphate droplets were used as an extractant to separate and enrich gold from the sample solution; finally, gold in the droplets was determined using high-resolution continuum source graphite furnace atomic absorption spectrometry. The experimental results showed that by using 2.5μL of tributyl phosphate (chloroform volume fraction 20%) as the extractant, gold can be extracted from a sample solution in 10% hydrochloric acid medium for 2min, and the enrichment factor for gold can reach up to 283 times. Under the selected experimental conditions, the mass concentration of gold showed a good linear relationship with its absorbance values in the range of 0.1 to 2.0ng/mL. The correlation coefficient (r) was 0.999, and the detection limit of the method was 0.11ng/g. Interference tests showed that the presence of certain coexisting elements such as sodium, magnesium, and aluminum in the sample solution had no effect on the determination of gold. According to the experimental method, the gold content in five high-purity graphite samples was measured. The relative standard deviation (RSD, n=6) of the results was 1.5%−4.9%, and the recovery rate was 94.9%−105.3%.
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表 1 金的石墨炉升温程序
Table 1. The heating program for graphite furnace of Au
步骤编号 升温程序 温度
(℃)斜坡
(℃/s)保持时间
(s)载气流速
(L/min)1 干燥 90 6 10 2 2 干燥 100 3 20 2 3 干燥 150 5 10 2 4 灰化 300 100 20 2 5 灰化 500 250 10 2 6 调零 950 0 5 0 7 原子化 2000 1500 5 0 8 清洗 2450 500 5 2 
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表 2 CCD检测器有效像素点的优化
Table 2. Effective pixel optimization of CCD detector
有效像素点 校准曲线斜率 检出限
(ng/g)方法标准偏差
(ng/mL)1 0.1134 0.153 0.03899 3 0.1653 0.121 0.02793 5 0.1758 0.109 0.02375 7 0.1801 0.093 0.02287 9 0.1865 0.097 0.02203
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表 3 方法精密度和加标回收实验
Table 3. The precision and recovery tests of the method
样品编号 6次分次测定值
(ng/g)平均值
(ng/g)RSD
(%)加标量
(ng/g)测定总量
(ng/g)回收率
(%)GC-1 3.10 3.16 3.02 3.13 3.18 3.31 3.15 1.5 2.00 5.03 94.9 GC-2 5.89 5.80 5.90 5.93 5.83 5.92 5.88 4.3 5.00 11.06 102.6 GC-3 9.34 9.57 9.21 9.51 9.45 9.37 9.41 4.9 10.00 19.88 103.7 GC-4 12.07 11.91 12.33 12.23 11.88 12.32 12.12 4.5 10.00 22.02 97.9 GC-5 15.03 15.21 14.85 14.79 14.89 15.10 14.98 4.9 15.00 30.58 105.3
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表 4 不同分离富集和检测方法性能的对比
Table 4. Comparison of performance of different seperation, enrichment and measurement methods
分离富集方法 时间
(min)方法检出限
(ng/g)RSD
(%)检测方法 参考文献 悬滴微萃取 2 0.11 1.5～4.9 (n=6) 石墨炉原子吸收光谱法(GFAAS) 本文方法 泡塑吸附法 60 0.08 ≤23.2 (n=9) 火焰原子荧光光谱法(FAFS) ［1］ 泡塑吸附法 20 6.6 0.81～2.11 (n=10) 电感耦合等离子体发射光谱法(ICP-OES) ［2］ 泡塑吸附法 60 0.15 / 电感耦合等离子体质谱法(ICP-MS) ［19］ 介孔吸附法 180 2.0 / 火焰原子吸收光谱法(AAS) ［26］ 火试金法 60 / 1.5～2.1 (n=7) 火焰原子吸收光谱法(AAS) ［9］ 铅试金法 60 5.3 2.3～3.7 (n=6) 火焰原子吸收光谱法(AAS) ［10］ 铋试金法 70 / 3.6～6.1 (n=5) 石墨炉原子吸收光谱法(GFAAS) ［11］ 离子树脂交换法 ＞60 / ＜3.5 (n=5) 火焰原子吸收光谱法(AAS) ［27］ 共沉淀法 180 20.6 / 电感耦合等离子体发射光谱法(ICP-OES) ［18］
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