加速器质谱测量树木年轮中不可交换有机氚的样品制备方法
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摘要
树木年轮具有良好的分年特性,其中的纤维素不会被分解供能,纤维素中不可交换有机氚(Nonexchangeable organically bound tritium, NE-OBT)难与其它物质产生交换,无流动性,能够准确地反映环境中的历史氚水平。使用加速器质谱(Accelerator mass spectrometry, AMS)进行测量,只需10 mg纤维素和200 s测量时间,比传统液体闪烁计数法更适于测定树木年轮中的NE-OBT。本研究改进了树木年轮中NE-OBT的AMS样品的制备过程。用次氯酸钠处理法取代酸碱酸处理法提取样品的纤维素,使纤维素的纯度从64.8%提升至83.9%。通过两步法将提取得到的纤维素转化为加速器质谱可以测量的氢化钛粉末样品。严格控制高温氧化时的纤维素量在10.00～10.05 mg之间、高温氧化时间从4 h延长到10 h、水在真空系统中的转移时间在1 min以上和冷阱温度在-88℃～-80℃之间,采用开门冷却等手段和措施,实现了AMS样品制备过程中同位素效应的稳定,建立了规范的NE-OBT AMS制样流程。在T/H的同位素丰度比为10~5～10~7TU时,标样的加速器质谱测量结果与液体闪烁计数法测量结果双对数线性回归拟合的相关性系数R~2=0.99912,表明本研究制备的样品能够用于加速器质谱测量,通过多量级标样标定校准后,可以得到准确的测量数值。
Tree rings can reflect the environmental conditions during tree growing period. The celluloses of tree rings will not be reutilized for energy. The nonexchangeable organically bound tritium(NE-OBT) in celluloses has no liquidity and no exchange with other things, so it can accurately reflect the historical tritium level in the local environment. The measurement of NE-OBT in tree rings using accelerator mass spectrometer(AMS) needs only 10 mg of celluloses and a 200-s measurement time, which is more suitable compared with liquid scintillation counter(LSC). In this study, the principle of sample preparation for AMS NE-OBT measurement of tree rings was systematically studied. Through modification of the extraction methods for cellulose, the purity of cellulose was raised from 64.8% to 83.9%. With the developed two-step method, the cellulose was transformed into titanium hydride which could be measured using accelerator mass spectrometry directly. By strictly controlling the combustion cellulose amounts between 10.00 and 10.05 mg, extending the combustion time from 4 h to 10 h, strictly controlling the water transfer time in the vacuum system above 1 min and the cold trap temperature between-88℃ to-80℃, and cooling down with an open door, etc., the isotopic fraction effect during sample pretreatment was depressed and stabilized. Measurement results of 10~5-10~7 TU standard samples by LSC and AMS were treating with linear regression on the double logarithmic axis. After fitting, the correlation coefficient R~2 reached 0.99912. These results proved that the prepared sample by this method could be used for measurement by accelerator mass spectrometry. Accurate measurement could be obtained after calibration with multi-level standards.
Tree rings can reflect the environmental conditions during tree growing period. The celluloses of tree rings will not be reutilized for energy. The nonexchangeable organically bound tritium(NE-OBT) in celluloses has no liquidity and no exchange with other things, so it can accurately reflect the historical tritium level in the local environment. The measurement of NE-OBT in tree rings using accelerator mass spectrometer(AMS) needs only 10 mg of celluloses and a 200-s measurement time, which is more suitable compared with liquid scintillation counter(LSC). In this study, the principle of sample preparation for AMS NE-OBT measurement of tree rings was systematically studied. Through modification of the extraction methods for cellulose, the purity of cellulose was raised from 64.8% to 83.9%. With the developed two-step method, the cellulose was transformed into titanium hydride which could be measured using accelerator mass spectrometry directly. By strictly controlling the combustion cellulose amounts between 10.00 and 10.05 mg, extending the combustion time from 4 h to 10 h, strictly controlling the water transfer time in the vacuum system above 1 min and the cold trap temperature between-88℃ to-80℃, and cooling down with an open door, etc., the isotopic fraction effect during sample pretreatment was depressed and stabilized. Measurement results of 10~5-10~7 TU standard samples by LSC and AMS were treating with linear regression on the double logarithmic axis. After fitting, the correlation coefficient R~2 reached 0.99912. These results proved that the prepared sample by this method could be used for measurement by accelerator mass spectrometry. Accurate measurement could be obtained after calibration with multi-level standards.
引文
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14 SHI Xu-Yang, QIAN Cheng, LIU Yan, LIU Xin-Tong, SHANG Xin, LIU Shuo, LIU Yu-Ting, YU Yun-Bo, ZHANG Jun, REN Xiao-Dong. Chinese J. Anal. Chem., 2018, 46(9): 1501-1506史旭洋, 钱程, 刘艳, 刘心同, 尚鑫, 刘硕, 刘禹廷, 于藴波, 张军, 任晓冬. 分析化学, 2018, 46(9): 1501-1506
15 Ma M, Wang L, Wang Y, Xiang W, Lyu P, Tang B, Tan X. J. Alloys Compd., 2017, 709: 445-452
16 WANG Yao-Qi, REN Xue-Ping, HOU Hong-Liang, ZHANG Yan-Ling, ZHANG Jian-Guo. Materials Science and Engineering of Powder Metallurgy, 2015, 20(1): 1-6王耀奇, 任学平, 侯红亮, 张艳苓, 张建国. 粉末冶金材料科学与工程, 2015, 20(1): 1-6
17 HUANG Gang, CAO Xiao-Hua, LONG Xing-Gui. China Nuclear Science and Technology Report, 2008, (1): 42-50黄刚, 曹小华, 龙兴贵. 中国核科技报告, 2008, (1): 42-50
2 Du L, Shan J, Ma Y H, Wang L, Qin L L, Pi L, Zeng Y S, Xia Z H, Wang G H, Liu W. Appl. Radiat. Isotopes, 2016, 110: 218-223
3 Galeriu D, Melintescu A, Strack S, Atarashi-Andoh M, Kim S B. J. Environ. Radioactiv., 2013, 118(4): 40-56
4 SHEN Hui-Fang, HUANG Yu, YANG Hai-Lan, LIU Wei. Atomic Energy Science and Technology, 2016, 50(6): 1147-1152申慧芳, 黄豫, 杨海兰, 刘卫. 原子能科学技术, 2016, 50(6): 1147-1152
5 HUANG Xiao-Mei, XIAO DING-Mu, QIN Ning-Sheng. Arid Land Geography, 2018, 41(5): 1001-1008黄小梅, 肖丁木, 秦宁生. 干旱区地理, 2018, 41(5): 1001-1008
6 Ko Y G, Kim C J, Cho Y H, Chung K H, Kang M J. J. Hazard. Mater., 2017, 331: 13-20
7 Kim S B, Roche J. J. Environ. Radioactiv., 2013, 122(4): 79-85
8 King S E, Phillips G W, August R A, Beach L A, Cutchin J H, Castaneda C. Nuclear Inst. Methods Phys. Res. B, 1987, 29(1): 14-17
9 Love A H, Hunt J R, Roberts M L, Southon J R, Chiarappa-Zucca M L, Dingley K H. Environ. Sci. Technol., 2002, 36(13): 2848-2852
10 Love A H, James R H, John P K. Environ. Sci. Technol., 2003, 37(19): 4330-4335
11 LIU Xiao-Hong, LIU Yu, XU Guo-Bao, CAI Qiu-Fang, AN Wen-Ling, WANG Wen-Zhi. Journal of Glaciology and Geocryology, 2010, 32(6): 1242-1250刘晓宏, 刘禹, 徐国保, 蔡秋芳, 安文玲, 王文志. 冰川冻土, 2010, 32(6): 1242-1250
12 LI Chun-Guang, DONG Ling-Ye, JI Yang-Yang, ZHU Yun-Feng, FANG Shan-Shan. Chinese Agricultural Science Bulletin, 2010, 26(22): 350-354李春光, 董令叶, 吉洋洋, 朱运峰, 方姗姗. 中国农学通报, 2010, 26(22): 350-354
13 Ma Y H, He M, Gao J, Qin L L, Deng K, Liu J Y, Yang G, Zhang Q, Ma Z W, Wei F, Zeng Y S, Liu W, Li Y. Nuclear Instrum. Methods Phys. Res. B, 2018, DOI: 10.1016/j.nimb.2018.09.042
14 SHI Xu-Yang, QIAN Cheng, LIU Yan, LIU Xin-Tong, SHANG Xin, LIU Shuo, LIU Yu-Ting, YU Yun-Bo, ZHANG Jun, REN Xiao-Dong. Chinese J. Anal. Chem., 2018, 46(9): 1501-1506史旭洋, 钱程, 刘艳, 刘心同, 尚鑫, 刘硕, 刘禹廷, 于藴波, 张军, 任晓冬. 分析化学, 2018, 46(9): 1501-1506
15 Ma M, Wang L, Wang Y, Xiang W, Lyu P, Tang B, Tan X. J. Alloys Compd., 2017, 709: 445-452
16 WANG Yao-Qi, REN Xue-Ping, HOU Hong-Liang, ZHANG Yan-Ling, ZHANG Jian-Guo. Materials Science and Engineering of Powder Metallurgy, 2015, 20(1): 1-6王耀奇, 任学平, 侯红亮, 张艳苓, 张建国. 粉末冶金材料科学与工程, 2015, 20(1): 1-6
17 HUANG Gang, CAO Xiao-Hua, LONG Xing-Gui. China Nuclear Science and Technology Report, 2008, (1): 42-50黄刚, 曹小华, 龙兴贵. 中国核科技报告, 2008, (1): 42-50