Determination of Oxygen Isotopic Composition in Barium Sulfate by Online Pyrolysis Method with Nickel-plated Carbon as Reductant
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摘要: 测定矿物或水中硫酸根的氧同位素组成（δ18O）能够识别物质来源及转化过程，常用的方法是将硫酸根转化为硫酸钡再用离线或在线法测试其δ18O值。目前普遍采用1420℃在线测试硫酸钡的氧同位素组成，该方法极易缩短反应炉的寿命，通过添加还原剂碳可以降低反应温度，但是已有报道对于添加还原剂后的反应温度讨论较少。本文选择镀镍碳（Ni-C）作为还原剂，将样品经Ni-C高温处理后进行一系列条件实验，确认了采用元素分析仪-稳定同位素质谱仪（EA-IRMS）测定硫酸钡中氧同位素组成的分析方法的关键技术参数：硫酸钡在线反应温度为1350℃；Ni-C与硫酸钡样品量的质量比范围选择0.73~2.15；为了获得更加精确的数据，硫酸钡与Ni-C用量都控制在700±100μg。在以上实验条件下，EA/HT-IRMS测定硫酸钡δ18O值的精密度为±0.12‰~±0.26‰，优于在线法已报道的精密度±0.20‰~±0.50‰。本方法在满足测试精密度的前提下，通过添加Ni-C降低了硫酸钡在线反应温度，延长了反应炉使用寿命。
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关键词:
- 硫酸钡 /
- 元素分析-稳定同位素质谱法 /
- 氧同位素 /
- 镀镍碳 /
- 在线高温裂解
Abstract:BACKGROUNDThe oxygen isotopic composition of sulfate radical in mineral or water can be used to identify the source and transformation process. At present, the common method is to convert sulfate radical into barium sulfate and the oxygen isotopic composition determined offline or online. It is possible to shorten the working life of the furnace when δ18O of barium sulfate is measured online under 1420℃. The reaction temperature can be reduced by adding reductant carbon, but there is less discussion about the reaction temperature reported. OBJECTIVESTo confirm the key technical parameters during determination of oxygen isotope composition in barium sulfate online. METHODSNickel-plated carbon was added in a series of conditional experiments during determination of oxygen isotope composition of barium sulfate by elemental analysis/isotope ratio mass spectrometry (EA-IRMS). RESULTS1350℃ was chosen as the online pyrolysis temperature of barium sulfate by adding Ni-C. The sample size ratio between Ni-C and BaSO4 was set as 0.73-2.15. The sample weight of Ni-C and BaSO4 was 700±100μg, respectively. Under the above conditions, the precision of δ18O of BaSO4 measured by EA/HT-IRMS was ±0.12‰-±0.26‰, better than the reported results of ±0.20‰-±0.50‰. CONCLUSIONSOn the premise of better precision, the online pyrolysis temperature of barium sulfate can be reduced to 1350℃ and the lifetime of the reactor can be improved by adding Ni-C. -
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表 1 不同Ni-C/BaSO4质量比值测试数据
Table 1. Measurement results for different ratio of Ni-C/BaSO4
参数 第1次 第2次 第3次 第4次 第5次 第6次 BaSO4质量(μg) 791 778 793 725 738 708 Ni-C质量(μg) 279 570 931 1182 1588 2362 Ni-C/BaSO4质量比值 0.35 0.73 1.17 1.63 2.15 3.34 离子流强度(mV) 12759 12943 13108 12132 12318 11845 离子流强度/BaSO4
质量比值(mV/μg)16.13 16.64 16.53 16.73 16.69 16.73 δ18O(‰) 8.48 8.52 8.59 8.69 8.39 7.97 
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表 2 BaSO4不同样品量测试数据
Table 2. Measurement results for different amounts of BaSO4 sample
参数 第1次 第2次 第3次 第4次 第5次 第6次 第7次 第8次 第9次 BaSO4质量(μg) 305 392 519 636 703 802 822 939 1052 Ni-C质量(μg) 292 376 505 739 766 1279 675 946 1105 m/z 28离子流强度(V) 4.88 6.40 8.73 10.63 11.72 13.30 13.59 15.61 17.44 δ18OVSMOW(‰) 8.99 9.33 8.92 8.72 8.67 8.58 8.63 8.33 8.14
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