高精度镉同位素分析样品消解方法对比研究

Comparison of Sample Digestion Methods for High Precision Cadmium Isotope Analysis

为考察不同消解方法的优缺点以及对不同基质样品(沉积物和大米)Cd同位素组成的影响,该文采用干法灰化法、酸提取法、微波消解法和高温高压密闭消解法等消解方法对水系沉积物(GSD)进行消解处理,比较了不同消解方法对沉积物Cd同位素组成测定的影响。随后使用微波消解法和高温高压密闭消解法对大米标准物质以及实际大米样品进行了消解。结果表明:高温高压密闭消解法所获得的沉积物Cd同位素测试结果在国内外文献报道的参考值范围内,能够满足同位素测定要求。而使用干法灰化法和酸提取法消解样品时,由于存在元素损失或消解不完全,标准物质Cd元素的回收率偏低(低至72.8%),导致同位素测试结果显著偏离真实值(Δ^(114/110)Cd值最大偏差达0.24‰)。微波消解法处理标准物质Cd元素的回收率在96.6%~98.8%范围内,且同位素测试结果与高温高压密闭消解法结果吻合良好(Δ^(114/110)Cd≤±0.04‰),表明微波消解法可以满足沉积物Cd同位素的测定要求,能够获得准确的Cd同位素组成数据。对大米标准物质和实际大米样品进行消解,所获得的Cd同位素测试结果与上述沉积物样品结果相同(Δ^(114/110)Cd≤±0.04‰),进一步验证了微波消解法的可靠性,证实微波消解法可用于沉积物及植物样品(大米)Cd同位素分析的快速消解。

With the development of multiple-collector inductively coupled plasma mass spectrometry(MC-ICP-MS),non-traditional stable isotope system has received increasing interest.Meanwhile,cadmium(Cd)isotope is becoming a research hotspot in recent years due to its unique physicochemical properties and isotopic fractionation characteristics.In addition,Cd isotope has been widely used in the fields of marine chemistry,biochemistry and cosmic chemistry.Sample digestion is a vital step in the process of isotope analysis,and the quality of digestion method directly determines the accuracy of Cd isotope data.In the previous studies,the Cd isotope data obtained by different digestion methods had been investigated for some geological and environmental samples,but few reports had been focusing on the Cd isotope composition of biological samples,e.g.rice flour reference materials.Therefore,the advantages and disadvantages of different digestion methods as well as the effects of sample digestion methods on the Cd isotopic composition of plant samples(rice,reference materials and real rice samples)were further compared.Firstly,dry ashing,acid extraction,microwave digestion and high temperature digestion bombs method were used to digest seven stream sediment(GSD)reference materials,and the effects of sample digestion methods on the high precision Cd isotope detection were evaluated.After that,both microwave acid digestion and high temperature digestion bombs method were used to digest the two rice(GBW)reference materials and six real rice samples.Results showed that the Cd isotope results of stream sediment reference materials obtained by the high temperature digestion bombs were in good agreement with the reported values.However,in the case of dry ashing or acid extraction method,the recoveries for Cd in the stream sediment reference materials were a little too low(it could be as low as 72.8%)due to element loss or incomplete digestion,and the Cd isotope test results would significantly deviate from the true value(maximum deviation of the isotope valueΔ^(114/110)Cd reached to 0.24‰).It is worth noting that microwave digestion could achieve a recovery for Cd within 96.6%-98.8%,and the isotope results are in line with the values obtained by high temperature digestion bombs method within the analytical uncertainty(Δ^(114/110)Cd≤±0.04‰),which indicated that the microwave digestion method could be used to obtain accurate and reliable Cd isotope data.In the follow-up digestion of two rice reference materials and six real rice samples,the Cd isotope compositions obtained were the same as those of the above stream sediment reference materials(Δ^(114/110)Cd≤±0.04‰),further verifying the reliability of microwave acid digestion.All the results demonstrated that microwave digestion was a reliable digestion method for Cd isotope analysis on samples of different matrix types.