【作者】 徐娟；

【导师】 刘勇胜； 胡兆初；

【作者基本信息】 中国地质大学 ， 地球化学， 2009， 硕士

【摘要】 电感耦合等离子体质谱（ICP-MS）具有灵敏度高、精密度好、检出限低、多元素同时检测并可提供同位素比值信息的分析特性,被广泛用于不同类型样品微量元素组成的分析研究。但是,对于地质样品中的痕量元素,由于基质复杂,存在的干扰严重而难以用ICP-MS进行直接准确测定。很多研究者采用了分离富集的样品预处理方式。但是这种方法步骤繁琐,难以操作。本研究建立了膜去溶装置（DSN）与ICP-MS联用的方法,能有效去除溶剂,显著提高元素信号灵敏度,有效降低氧化物和氢氧化物产率,结合N₂增敏技术,能够对地质样品中微量Ag准确测定而无需预分离富集步骤。测定了21个各种类型地质标准样品和103个各种类型实际样品,验证了建立方法的可行性。激光剥蚀-电感耦合等离子体（LA-ICP-MS）技术具有原位（in stiu）、实时（real time）、快速的分析优势和灵敏度高、空间分辨率好的特点,成为一种新的从微观角度研究物质组成及分布特征的分析测试手段。这种技术在地质样品测定中已经被广泛应用,其中对锆石U-Pb年龄和微量元素组成的测定是近年来的一个热点。对年龄较老的锆石测定已经建立了比较成熟的方法,但是对于年轻锆石的测定方法还处于研究阶段,并且为TIMS和LA-MC-ICP-MS的测定结果。本研究利用LA-ICP-MS对新近纪以来锆石U-Pb年龄和微量元素组成进行了分析测定,采用增大激光剥蚀斑束（44μm）和加入适量N₂的方法来增加检测灵敏度,利用ICPMSDataCal软件来处理锆石年龄和微量元素组成。通过对样品的多次测定和对标准锆石的分析验证了建立方法的准确性。一、DSN-ICP-MS直接测定地质样品中Ag的研究:（1）常规ICP-MS测定地质样品中的Ag时,通常地质样品中Zr,Nb,Y的含量相对Ag的含量高得多,⁹⁰Zr,⁹¹Zr以及⁸⁹Y和⁹³Nb的氧化物和氢氧化物的严重干扰,导致冷却雾室ICP-MS不能准确测定地质样品中Ag;（2）最佳化条件下,DSN-ICP-MS的信号强度比常规ICP-MS提高一倍,氧化物和氢氧化物产率降低2个数量级,使得能够直接准确测定地质样品中的低含量Ag;（3）微量N₂的加入能够明显提高灵敏度,显著降低氧化物和氢氧化物产率,可能是由于生成了部分氮的氧化物和氢氧化物,从而减少了被分析物与O和OH结合的机会。但是氮的加入又会引起多原子离子干扰,因此要以实际情况选取适量的氮气;（4） DSN-ICP-MS对Ag的分析检测限为0.0005ng/mL,对比常规ICP-MS的检测限0.015ng/mL降低了2个数量级,保证了低含量Ag的准确测定;（5）对103个各种类型岩石样品的测定结果表明,利用同位素¹⁰⁷Ag和¹⁰⁹Ag分别获得的结果有很好的一致性,进一步证明了利用DSN-ICP-MS测定地质样品时,能够有效去除氧化物和氢氧化物的干扰。另外,对21个各种类型地质标准样品的分析结果显示,测定值和推荐值有很好的吻合性,确证了DSN-ICP-MS准确测定地质样品中低含量Ag的准确性。以上所建立的DSN-ICP-MS准确测定地质样品中低含量Ag的方法,克服了传统预富集分离方法步骤繁琐,难以操作的缺点,具有快速、有效的特点。二、利用LA-ICP-MS对新近纪以来锆石U-Pb定年和微量元素同时测定的研究:（1）最佳N₂流速时,LA-ICP-MS对大多数元素的信号强度比N₂流速为0ml/min时提高了1.5-2.5倍,验证了N₂在LA-ICP-MS测定中具有增敏效应。（2）用国际标准锆石91500作外标,对标准锆石GJ-1和SK10-2校正结果显示,GJ-1的²⁰⁶Pb/²³⁸U年龄单点相对偏差（2σ）小于2.2%,²⁰⁶Pb/²³⁸U年龄加权平均值的相对偏差2σ小于0.2%。实验室内部的标准锆石SK10-2（31Ma,Pb≈7.5μg/g）²⁰⁶Pb/²³⁸U年龄的单点相对偏差（2σ）为1.9～2.6%,²⁰⁶Pb/238U年龄加权平均值的相对偏差2σ小于2%。这些锆石测定结果的年龄加权平均值与推荐值（或已发表的值）在误差范围内一致;（3）锆石中微量元素组成的测定,采用了ICPMSDataCal软件中Si内标,BCR-2G,BHVO-2G,BIR-1G多外标校正方法进行数据处理。利用不同的分析方法对标准锆石91500和GJ-1进行多次分析测定,验证了所采用的Si内标多外标方法的准确性;（4）利用所建立方法,对Pb,U含量很低（Pb含量在0.0sμg/g～0.1μg/g,U含量在20μg/g～50μg/g）的新近纪以来锆石巨晶HN-1,HF4-7,HM-1进行多次测定,U-Pb年龄和微量元素含量具有良好的重现性。以上结果表明,所建立的分析测试方法对于1-10Ma的锆石巨晶,可以同时准确获得锆石的U-Pb年龄和微量元素组成。更多还原

【Abstract】 During the last decades inductively coupled plasma-mass spectrometry（ICP-MS） has been developed into an accurate and sensitive technique for multi-element determinations in a range of sample matrices.Compared with AFS,AAS and ICP-AES,ICP-MS offers better sensitivity and excellent accuracy with multi-element and isotope ratio measurement capabilities.However,the low abundance of trace elements makes the direct determination of silver in geological samples very challenging.Most methods require separation and pre-concentration of trace elements from complex matrices.Membrane desolvation system（DSN） is very effective to increases sensitivity and reduces the oxide and hydroxide interferences by removing water vapor.A method for direct determination of Ag by DSN-ICP-MS in geological samples has been developed.Laser ablation inductively coupled plasma-mass spectrometry（LA-ICP-MS）is an accurate and precise in situ and real time technique for trace element analysis of a wide variety of solid samples.It has becomes a powerful method,providing age and trace element data comparable to those of SIMS in both accurary and precision but with significantly high throughputs.U-Pb dating and trace elements of zircon megacrysts（1-10Ma） from three different places were studied in this work.Zircon standards 91500,GJ-1,SK10-2 and zircon megacrysts were detemined by LA-ICP-MS at a spot size of 44μm and 5ml/min N₂ adding.The results of zircon standards are agree with the reference valus and published values.The main results were summarized as following:1.Determination of Ag in geological samples by DSN-ICP-MS.1) Compared with the results obtained by using conventional ICP-MS,the signals intensity by DSN-ICP-MS were improved the oxide and hydroxide ratios were found to be reduced remarkably.The significant reduced oxide and hydroxide interferences should be attributed to the elimination of water vapor in sample aerosol.2) Increasing nitrogen addition leads to decrease in oxide and hydroxide ratios and increase in signal intensity.The removal of oxygen through NO formation was advocated as the dominant reason for the reduction of the oxide and hydroxide ratio.3) The determined concentration values of Ag by conventional ICP-MS are much higher than those obtained by membrane desolvation-ICP-MS.Most of the results obtained by menbrane desolvation ICP-MS are in good agreement with the reference values.This indicates that the equivalent concentrations of Ag caused by oxide and hydroxide interferences of Zr are far more than the actual concentration of Ag in geological samples.2.U-Pb dating and trace elements analysed of zircon megacrysts by LA-ICP-MS.1) To addition of 5ml/min nitrogen to the central channel gas in LA-ICP-MS increases the sensitivity for most of the 65 investigated elements by a factor of 1.5-2.5.2) Zircon standard 91500 was used as an external satandard for correcting mass discrimination and isotope fractionation for U-Pb dating,which was analyzed twice every 5 analyses of zircon samples.Zircon standards GJ-1,SK10-2 and zircon megacrysts were calculated by 91500.The results of GJ-1 and SK10-2 are agree with the reference valus or published values.3) The USGS glasses BCR-2G and BIR-1G were used as multi-calibration standards for external calibration of trace elements.4) U-Pb dating and trace elements of zircon megacrysts（1-10Ma） from three different places were analysed by the founded method,and got the satisfying results.更多还原