-
摘要:
多接收电感耦合等离子体质谱(MC-ICP-MS) 因具有样品通量高、ICP源电离能力强、质量分辨率高等优点，被广泛应用于同位素比值的精确测量。几十年来，标样-样品-标样间插法(SSB)一直用于校正仪器测量过程中的质量歧视，以获得准确的同位素组成结果，但在待测样品含量较低时，测量结果容易受到背景信号的影响。“On Peak Zero”校正将背景信号从总测试信号中扣除，是一种有效的扣除背景干扰的方法，并已得到广泛的应用，但尚没有系统探究这种校正背后的数学原理。本文通过数学推导和近似替代建立了同位素组成受背景信号影响的数学公式，并对不同浓度的Li、S、Fe、Sr、Nd和Pb标准溶液进行实验分析，对运用“On Peak Zero”方法校正这些同位素测试值的数学原理进行了阐述。研究结果表明：目标元素浓度越低，空白溶液的信号强度对待测样品分析准确度的影响越大，而“On Peak Zero”方法可以较好地消除空白溶液对样品测试的影响。本文以实验结果为基础展示了对该数学公式的数据拟合，模拟结果与本文研究的实际实验结果保持一致。该模型很好地解释了背景浓度对同位素测试值的影响，有助于理解“On Peak Zero”校正在多接收等离子体质谱同位素分析中的应用。
-
关键词:
- 多接收电感耦合等离子体质谱法(MC-ICP-MS) /
- 同位素分析 /
- 背景干扰 /
- On Peak Zero /
- 数学模拟
Abstract:BACKGROUND Multi-collector inductively coupled plasma-mass spectrometry (MC-ICP-MS) has been widely applied to accurate and precise measurements of isotope ratios due to its high sample throughput, strong ionization ability of ICP sources and high mass resolution. For decades, the standard-sample bracketing (SSB) method has been used to correct for instrumental mass bias during the measurement to achieve accurate results. When the content of the target isotope in samples is low, the measurement results are easily influenced by the background signals. "On Peak Zero" correction deducts the background signal from the total signal, which is an effective method to eliminate the background interference and has been widely used, but no research has been conducted to systematically explore the mathematical principles behind this correction.
OBJECTIVES To establish a mathematical model for the "On Peak Zero" correction, and verify its confidence by applying it to isotope measurements of different concentrations of Li, S, Fe, Sr, Nd and Pb standard solutions.
METHODS In this study, a mathematical model of the influence by the background signal on isotopic composition was established by mathematical reasoning and approximate substitution. Standard solutions of different concentrations of Li, S, Fe, Sr, Nd and Pb were prepared for the application of the "On Peak Zero" method through experimental analysis. Two types of blank signals were subtracted separately from the aggregate signals to simulate isotope measurements without and with "On Peak Zero" correction.
RESULTS The results indicate that the lower the concentration of the target element, the greater is the blank solution signal influence on the accuracy of the sample to be tested, and the "On Peak Zero" method can better eliminate the influence of the blank solution on the sample measurements. The simulation results based on this model were consistent with the real experimental results in this study.
CONCLUSIONS The mathematical model and the data explain well the effect of background concentration on the experimental isotope values, and are useful for understanding the application of the "On Peak Zero" method in MC-ICP-MS isotope analysis.
-
-
表 1 MC-ICP-MS测试使用的Li、S、Fe、Sr、Nd、Pb标准物质编号、浓度及信号强度
Table 1. Reference materials, concentrations and signal intensities of Li, S, Fe, Sr, Nd and Pb used in MC-ICP-MS measurements
元素 标准物质编号 工作标样浓度(μg/L) 样品溶液浓度(μg/L) 工作标样信号强度(V) Li NIST SRM 8545 100 分别为：10, 20, 40, 60, 80, 200, 300, 400, 500 ~1.4 S AS 10000 分别为：1000, 3000, 5000, 7000, 9000, 15000, 20000 ~3.7 Fe IRMM-14 1000 分别为：100, 200, 400, 600, 800, 2000, 3000 ~8.5 Sr NIST SRM 987 200 分别为：20, 40, 80, 120, 160, 400, 600, 800 ~8.0 Nd JNdi-1 200 分别为：20, 40, 80, 120, 160, 400, 600, 800, 1000, 2000 ~2.8 Pb NIST SRM 981 200 分别为：20, 40, 80, 120, 160, 400, 600, 800, 1000 ~5.6 注：信号强度是所研究元素丰度最高的同位素的信号强度。 
下载: 导出CSV
表 2 Neptune Plus MC-ICP-MS同位素测试的主要操作条件设置和参数
Table 2. Main operating conditions and parameters for isotopic measurements using Neptune Plus MC-ICP-MS
质谱仪及参数 工作条件设置 MC-ICP-MS ThermoFisher Neptune Plus 冷却气(Ar)流速 ~15L/min 辅助气(Ar)流速 ~0.90L/min 样品气(Ar)流速 ~1.028L/min 提取透镜电压 ~2000V 界面锥 Ni锥(H) 分析器压力 ~10-9Torr 射频正向功率 ~1200W 数据获取参数 工作条件设置 质量分辨率 S和Fe选择中质量分辨率；其余元素选择低质量分辨率 获取模式 静态 检测器 法拉第杯
下载: 导出CSV
表 3 每个元素的IBLK、Istdmix和ΔBLK-Analyte参数值
Table 3. IBLK, Istdmix and ΔBLK-Analyte values for each element
元素 IBLK
(V)Istdmix
(V)ΔBLK-Analyte
(‰)Li 0.0037 1.43 -609 S 0.005 3.74 -614 Fe 0.158 8.55 95 Sr 0.017 8.00 -45 Nd 0.0004 2.80 -26 Pb 0.0024 5.63 -115 注：“IBLK”和“Istdmix”表示信号强度是所研究元素的所有同位素的信号强度之和。ΔBLK-Analyt=δBLK-δAnalyte。对于每一种元素，工作标准溶液(例如，对Sr来说是200μg/L NIST SRM 987溶液)被用来当作计算ΔBLK-Analyte的标样。
下载: 导出CSV
-
[1] Albarède F, Telouk P, Blichert-Toft J, et al. Precise and accurate isotopic measurements using multiple-collector ICPMS[J]. Geochimica et Cosmochimica Acta, 2004, 68(12): 2725-2744. doi: 10.1016/j.gca.2003.11.024
[2] Yang L. Accurate and precise determination of isotopic ratios by MC-ICP-MS: A review[M]//Mass Spectrometry Reviews. John Wiley & Sons, 2009: 990-1011.
[3] Yang L, Tong S, Zhou L, et al. A critical review on isotopic fractionation correction methods for accurate isotope amount ratio measurements by MC-ICP-MS[J]. Journal of Analytical Atomic Spectrometry, 2018, 33(11): 1849-1861. doi: 10.1039/C8JA00210J
[4] Zhu X K, O'Nions R K, Guo Y, et al. Determination of natural Cu-isotope variation by plasma-source mass spectrometry: Implications for use as geochemical tracers[J]. Chemical Geology, 2000, 163(1-4): 139-149. doi: 10.1016/S0009-2541(99)00076-5
[5] Lin J, Liu Y, Hu Z, Yang L, et al. Accurate determination of lithium isotope ratios by MC-ICP-MS without strict matrix-matching by using a novel washing method[J]. Journal of Analytical Atomic Spectrometry, 2016, 31(2): 390-397. doi: 10.1039/C5JA00231A
[6] Lin A J, Yang T, Jiang S Y. A rapid and high-precision method for sulfur isotope δ34S determination with a multiple-collector inductively coupled plasma mass spectrometer: Matrix effect correction and applications for water samples without chemical purification[J]. Rapid Communications in Mass Spectrometry, 2014, 28(7): 750-756. doi: 10.1002/rcm.6838
[7] Bryant C J, McCulloch M T, Bennett V C. Impact of matrix effects on the accurate measurement of Li isotope ratios by inductively coupled plasma mass spectrometry (MC-ICP-MS) under "cold" plasma conditions[J]. Journal of Analytical Atomic Spectrometry, 2003, 18(7): 734-737. doi: 10.1039/B212083F
[8] Vanhaecke F, Dams R, Vandecasteele C. "Zone model" as an explanation for signal behaviour and non-spectral interferences in inductively coupled plasma mass spectrometry[J]. Journal of Analytical Atomic Spectrometry, 1993, 8(3): 433-438. doi: 10.1039/JA9930800433
[9] Loula M, Kaňa A, Mestek O. Non-spectral interferences in single-particle ICP-MS analysis: An underestimated phenomenon[J]. Talanta, 2019, 202: 565-571. doi: 10.1016/j.talanta.2019.04.073
[10] Lemarchand D, Gaillardet J, Göpel C, et al. An optimized procedure for boron separation and mass spectrometry analysis for river samples[J]. Chemical Geology, 2002, 182(2-4): 323-334. doi: 10.1016/S0009-2541(01)00329-1
[11] Fortunato G, Mumic K, Wunderli S, et al. Application of strontium isotope abundance ratios measured by MC-ICP-MS for food authentication[J]. Journal of Analytical Atomic Spectrometry, 2004, 19(2): 227-234. doi: 10.1039/b307068a
[12] Craddock P R, Rouxel O J, Ball L A, et al. Sulfur isotope measurement of sulfate and sulfide by high-resolution MC-ICP-MS[J]. Chemical Geology, 2008, 253(3-4): 102-113. doi: 10.1016/j.chemgeo.2008.04.017
[13] Aggarwal J K, Sheppard D, Mezger K, et al. Precise and accurate determination of boron isotope ratios by multiple collector ICP-MS: Origin of boron in the Ngawha geothermal system, New Zealand[J]. Chemical Geology, 2003, 199(3-4): 331-342. doi: 10.1016/S0009-2541(03)00127-X
[14] Tanner S D. Space charge in ICP-MS: Calculation and implications[J]. Spectrochimica Acta Part B: Atomic Spectroscopy, 1992, 47(6): 809-823. doi: 10.1016/0584-8547(92)80076-S
[15] Maréchal C N, Télouk P, Albarède F. Precise analysis of copper and zinc isotopic compositions by plasma-source mass spectrometry[J]. Chemical Geology, 1999, 156(1-4): 251-273. doi: 10.1016/S0009-2541(98)00191-0
[16] Albarède F, Albalat E, Télouk P. Instrumental isotope fractionation in multiple-collector ICP-MS[J]. Journal of Analytical Atomic Spectrometry, 2015, 30(8): 1736-1742. doi: 10.1039/C5JA00188A
[17] Galer S J G. Optimal double and triple spiking for high precision lead isotopic measurement[J]. Chemical Geology, 1999, 157(3-4): 255-274. doi: 10.1016/S0009-2541(98)00203-4
[18] Moynier F, Agranier A, Hezel D C, et al. Sr stable isotope composition of Earth, the Moon, Mars, Vesta and meteorites[J]. Earth and Planetary Science Letters, 2010, 300(3-4): 359-366. doi: 10.1016/j.epsl.2010.10.017
[19] Fietzke J, Eisenhauer A. Determination of temperature-dependent stable strontium isotope (88Sr/86Sr) fraction-ation via bracketing standard MC-ICP-MS[J]. Geochemistry, Geophysics, Geosystems, 2006, 7(8): Q08009.
[20] Wieser M E, Buhl D, Bouman C, et al. High precision calcium isotope ratio measurements using a magnetic sector multiple collector inductively coupled plasma mass spectrometer[J]. Journal of Analytical Atomic Spectrometry, 2004, 19(7): 844-851. doi: 10.1039/b403339f
[21] Mason T F D, Weiss D J, Horstwood M, et al. High-precision Cu and Zn isotope analysis by plasma source mass spectrometry[J]. Journal of Analytical Atomic Spectrometry, 2004, 19(2): 218-226. doi: 10.1039/b306953b
[22] 秦燕, 徐衍明, 侯可军, 等. 铁同位素分析测试技术研究进展[J]. 岩矿测试, 2020, 39(2): 151-161. doi: 10.15898/j.cnki.11-2131/td.201908120120 http://www.ykcs.ac.cn/cn/article/doi/10.15898/j.cnki.11-2131/td.201908120120
Qin Y, Xu Y M, Hou K J, et al. Progress of analytical techniques for stable iron isotopes[J]. Rock and Mineral Analysis, 2020, 39(2): 151-161. doi: 10.15898/j.cnki.11-2131/td.201908120120 http://www.ykcs.ac.cn/cn/article/doi/10.15898/j.cnki.11-2131/td.201908120120
[23] Gou L F, Deng L. Determination of barium isotopic ratios in river waters on MC-ICP-MS[J]. Analytical Sciences, 2019, 35(5): 18P329.
[24] Magna T, Wiechert U H, Halliday A N. Low-blank isotope ratio measurement of small samples of lithium using multiple-collector ICPMS[J]. International Journal of Mass Spectrometry, 2004, 239(1): 67-76. doi: 10.1016/j.ijms.2004.09.008
[25] He M Y, Deng L, Lu H, et al. Elimination of the boron memory effect for rapid and accurate boron isotope analysis by MC-ICP-MS using NaF[J]. Journal of Analytical Atomic Spectrometry, 2019, 34(5): 1026-1032. doi: 10.1039/C9JA00007K
[26] Li J, Liang X R, Xu J F, et al. Simplified technique for the measurements of Re-Os isotope by multicollector inductively coupled plasma mass spectrometry (MC-ICP-MS)[J]. Geochemical Journal, 2010, 44(1): 73-80. doi: 10.2343/geochemj.1.0044
[27] 李杰, 梁细荣, 董彦辉, 等. 利用多接收器电感耦合等离子体质谱仪(MC-ICPMS)测定镁铁-超镁铁质岩石中的铼-锇同位素组成[J]. 地球化学, 2007, 36(2): 153-160. doi: 10.3321/j.issn:0379-1726.2007.02.004
Li J, Liang X R, Dong Y H, et al. Measurements of Re-Os isotopic composition in mafic-ultramafic rocks by multi-collector inductively coupled plasma mass spectrometer (MC-ICPMS)[J]. Geochemica, 2007, 36(2): 153-160. doi: 10.3321/j.issn:0379-1726.2007.02.004
[28] Pons M L, Millet M A, Nowell G N, et al. Precise measurement of selenium isotopes by HG-MC-ICPMS using a 76-78 double-spike[J]. Journal of Analytical Atomic Spectrometry, 2020, 35(2): 320-330. doi: 10.1039/C9JA00331B
[29] Liu S A, Li D, Li S, et al. High-precision copper and iron isotope analysis of igneous rock standards by MC-ICP-MS[J]. Journal of Analytical Atomic Spectrometry, 2013, 29(1): 122-133.
[30] 戴梦宁, 宗春蕾, 袁洪林. 高Rb/Sr岩石样品中Sr同位素多接收等离子体质谱分析校正方法研究[J]. 岩矿测试, 2012, 31(1): 95-102. doi: 10.3969/j.issn.0254-5357.2012.01.012 http://www.ykcs.ac.cn/cn/article/id/ykcs_20120113
Dai M N, Zong C L, Yuan H L. A calibration strategy of 87Sr/86Sr ratio for rocks with high Rb/Sr measured by multiple collector-inductively coupled plasma-mass spectrometry[J]. Rock and Mineral Analysis, 2012, 31(1): 95-102. doi: 10.3969/j.issn.0254-5357.2012.01.012 http://www.ykcs.ac.cn/cn/article/id/ykcs_20120113
[31] Woodhead J, Swearer S, Hergt J, et al. In situ Sr-isotope analysis of carbonates by LA-MC-ICP-MS: Interference corrections, high spatial resolution and an example from otolith studies[J]. Journal of Analytical Atomic Spectrometry, 2005, 20(1): 22-27. doi: 10.1039/b412730g
[32] Davidson J, Tepley F, Palacz Z, et al. Magma recharge, contamination and residence times revealed by in situ laser ablation isotopic analysis of feldspar in volcanic rocks[J]. Earth and Planetary Science Letters, 2001, 184(2): 427-442. doi: 10.1016/S0012-821X(00)00333-2
[33] Hu Y, Teng F Z. Optimization of analytical conditions for precise and accurate isotope analyses of Li, Mg, Fe, Cu, and Zn by MC-ICPMS[J]. Journal of Analytical Atomic Spectrometry, 2019, 34(2): 338-346. doi: 10.1039/C8JA00335A
[34] Bian X P, Yang T, Lin A J, et al. Rapid and high-precision measurement of sulfur isotope and sulfur concentration in sediment pore water by multi-collector inductively coupled plasma mass spectrometry[J]. Talanta, 2015, 132: 8-14. doi: 10.1016/j.talanta.2014.08.053
[35] Weyer S, Schwieters J B. High precision Fe isotope measurements with high mass resolution MC-ICPMS[J]. International Journal of Mass Spectrometry, 2003, 226(3): 355-368. doi: 10.1016/S1387-3806(03)00078-2
[36] Paton C, Hellstrom J, Paul B, et al. Iolite: Freeware for the visualisation and processing of mass spectrometric data[J]. Journal of Analytical Atomic Spectrometry, 2011, 26(12): 2508-2518. doi: 10.1039/c1ja10172b
[37] Rosner M, Ball L, Peucker-Ehrenbrink B, et al. A simplified, accurate and fast method for lithium isotope analysis of rocks and fluids, and δ7Li values of seawater and rock reference materials[J]. Geostandards and Geoanalytical Research, 2007, 31(2): 77-88. doi: 10.1111/j.1751-908X.2007.00843.x
[38] Hoefs J. Stable isotope geochemistry[M]. Springer Science & Business Media, 2009.
[39] El Meknassi S, Dera C T, de Rafélis M, et al. Sr isotope ratios of modern carbonate shells: Good and bad news for chemostratigraphy[J]. Geology, 2018, 46(11): 1003-1006. doi: 10.1130/G45380.1
[40] Lin J, Liu Y, Chen H, et al. Review of high-precision sr isotope analyses of low-Sr geological samples[J]. Journal of Earth Science, 2015, 26(5): 763-774. doi: 10.1007/s12583-015-0593-0
[41] Jeffcoate A B, Elliott T, Thomas A, et al. Precise/small sample size determinations of lithium isotopic compositions of geological reference materials and modern seawater by MC-ICP-MS[J]. Geostandards and Geoanalytical Research, 2004, 28(1): 161-172. doi: 10.1111/j.1751-908X.2004.tb01053.x
-
图(2)
表(3)
计量
- 文章访问数: 2668
- PDF下载数: 152
- 施引文献: 0