气体中甲烷单组分的色谱—真空低温富集方法及其同位素分馏效应

刘清梅; 李嘉成; 蒋文敏; 熊永强

doi:10.11781/sysydz202403621

气体中甲烷单组分的色谱—真空低温富集方法及其同位素分馏效应

doi: 10.11781/sysydz202403621

刘清梅^{1, 2, 3,},
李嘉成^{1, 2, 3},
蒋文敏^{1, 2},
熊永强^{1, 2, ,}

1.
中国科学院广州地球化学研究所, 有机地球化学国家重点实验室, 广州 510640
2.
中国科学院深地科学卓越创新中心, 广州 510640
3.
中国科学院大学, 北京 100049

基金项目:

国家自然科学基金项目“深层油气中甲烷团簇同位素地球化学研究” 42073065

详细信息

作者简介:
刘清梅(1996—)，女，博士生，从事团簇同位素地球化学研究。E-mail: liuqingmei@gig.ac.cn

通讯作者:
熊永强(1967—)，男，博士，研究员，从事分子有机地球化学研究。E-mail: xiongyq@gig.ac.cn

中图分类号: TE135
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出版历程
- 收稿日期: 2023-06-05
- 修回日期: 2024-03-28
- 刊出日期: 2024-05-28

Chromatography-vacuum low temperature method of methane enrichment and isotopic fractionation in gas samples

LIU Qingmei^{1, 2, 3
,},
LI Jiacheng^{1, 2, 3},
JIANG Wenmin^{1, 2},
XIONG Yongqiang^{1, 2
, ,}

1.
State Key Laboratory of Organic Geochemistry, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou, Guangdong 510640, China
2.
CAS Center for Excellence in Deep Earth Science, Guangzhou, Guangdong 510640, China
3.
University of Chinese Academy of Sciences, Beijing 100049, China

摘要

摘要: 甲烷(CH₄)团簇同位素分析在气候变化、能源勘探和行星生命等领域中发挥了重要作用。样品中CH₄的纯度直接了影响高分辨质谱团簇同位素分析的精度和准确性。针对气样中CH₄组分的富集纯化难题，根据气相色谱(GC)组分分离原理，实时监测组分峰形，进一步优化了载气线速、进样量等条件。同时，通过外标法量化回收率，GC组分分析验证纯度，保证纯化的有效性。通过优化色谱—真空低温富集制备方法，确定了IBEX系统载气最佳线速为12 mL/min，CH₄进样量需小于12 mL等实验条件，可视化GC峰形确保CH₄峰与相邻N₂干扰峰基本分离，实现了CH₄单组分的高纯富集。当气样中CH₄含量小于70%而空气含量较高时，需要进行二次纯化以提高CH₄纯度。讨论了5Å分子筛等吸附剂在纯化过程中可能引起CH₄同位素分馏的原因，并通过适当延长CH₄收集时间来消除5Å分子筛干扰。目前，该方法单次纯化过程约90 min，CH₄的回收率和纯度分别为90.1%~95.7%和97.3%~98.9%，对同位素组成(δ¹³C_VPDB和δD_VSMOW、Δ¹³CH₃D和Δ¹²CH₂D₂)的差异均小于质谱仪的分析误差，几乎可以忽略不计。
- 甲烷 /
- 气相色谱 /
- 纯度 /
- 回收率 /
- 同位素分馏
Abstract: Methane (CH₄) clumped isotope analysis plays a crucial role in the fields of climate change, energy exploration, and planetary research. The purity of CH₄ in samples directly affects the precision and accuracy of high-resolution mass spectrometry in clumped isotope analysis. Addressing the challenge associated with enriching and purifying CH₄ components in gas samples, this study optimized conditions such as carrier gas line speed and sample injection volume based on the principles of gas chromatography (GC) component separation, with real-time monitoring of component peak shapes. Additionally, the recovery rate was quantified using an external standard method and purity was verified through GC component analysis to ensure the effectiveness of the purification process. By optimizing the chromatography-vacuum low-temperature enrichment preparation method, the optimal carrier gas line speed for the IBEX system was determined to be 12 mL/min, with a CH₄ injection volume less than 12 mL. This facilitated visualization of GC peak shapes, thus ensured that the CH₄ peak was essentially separated from the adjacent N₂ interference peak, achieving high-purity enrichment of the CH₄ single component. When the CH₄ content in gas samples was less than 70% and the air content was high, secondary purification was required to improve CH₄ purity. The causes of CH₄ isotopic fractionation during purification using adsorbents like 5Å molecular sieves were discussed, and extending the CH₄ collection time was proposed to eliminate the interference from the 5Å molecular sieve. Currently, this method requires approximately 90 min for a single purification process, with CH₄ recovery and purity ranging from 90.1% to 95.7% and 97.3% to 98.9%, respectively. The differences in isotopic composition (δ¹³C_VPDB and δD_VSMOW, Δ¹³CH₃D, and Δ¹²CH₂D₂) are all less than the analytical error of the mass spectrometer, making them almost negligible.
- CH₄ /
- gas chromatography /
- purity /
- recovery rate /
- isotopic fractionation
注释:

利益冲突声明/Conflict of Interests

所有作者声明不存在利益冲突。

All authors disclose no relevant conflict of interests.

作者贡献/Authors’Contributions

刘清梅、蒋文敏参与实验设计；刘清梅、李嘉成完成实验操作；刘清梅、蒋文敏、熊永强参与论文写作和修改。所有作者均阅读并同意最终稿件的提交。

The experiment was designed by LIU Qingmei and JIANG Wenmin. The experimental operation was completed by LIU Qingmei and LI Jiacheng. The manuscript was drafted and revised by LIU Qingmei, JIANG Wenmin and XIONG Yongqiang. All authors have read the last version of the paper and consented to its submission.

HTML全文

图 1 甲烷纯化系统结构示意

Figure 1. Schematic structure of methane purification system

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图 2 甲烷同位素分析峰形

Figure 2. Peak shapes of methane isotopic analysis

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图 3 纯化气样SG-1甲烷纯化回收率

Figure 3. Methane purification recovery rate of purified gas sample SG-1

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图 4 混合气样SG-2纯化前后气相色谱(GC)组分分析

Figure 4. GC component analysis of mixed gas sample SG-2 before and after purification

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图 5 气相色谱的板高与载气线速关系

Figure 5. Relation curve between plate height and carrier gas line speed for gas chromatography

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图 6 气相色谱峰展宽效应

Figure 6. Peak broadening effect in gas chromatography

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表 1 甲烷气样SG-1纯化前后同位素组成对比

Table 1. Comparison of isotopic composition of methane gas sample SG-1 before and after purification

	δ¹³C_VPDB/‰	δD_VSMOW/‰	Δ¹³CH₃D/‰	Δ¹²CH₂D₂/‰	样品数
纯化前	-43.23	-182.78	2.65	2.14	5
纯化后	-43.30	-182.82	2.91	1.50	5

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表 2 通过改变载气线速纯化气样后甲烷回收率及纯度数据

Table 2. Recovery and purity data of methane after purification of gas sample by varying carrier gas line speed

样品	体积/mL	柱温/℃	载气流速/(mL/min)	峰面积			回收率/%	纯度/%
样品	体积/mL	柱温/℃	载气流速/(mL/min)	O₂	N₂	CH₄	回收率/%	纯度/%
SG-1	6	30	30	80.8	310.2	22 372.9	82.1	98.3
MG-20%	6	30	30	183.4	3 020.3	18 167.3	83.6	85.0
SG-1	6	30	20	99.1	347.4	23 279.6	85.5	98.1
MG-20%	6	30	20	187.2	1 804.5	18 913.2	87.1	90.5
SG-1	6	30	15	145.9	408.3	24 157.7	88.7	97.8
MG-20%	6	30	15	195.7	1 076.7	19 235.5	88.6	93.8
SG-1	6	30	12	112.2	353.6	25 940.1	95.2	98.2
MG-20%	6	30	12	177.3	415.1	20 831.4	95.9	97.2
SG-1	6	30	10	136.8	348.1	25 673.3	94.2	98.1
MG-20%	6	30	10	189.5	394.4	20 374.8	93.8	97.2
SG-1	9	30	12	92.7	384.2	38 221.7	93.1	98.8
SG-2	9	30	12	109.8	401.1	18 284.2	95.0	97.3
SG-1	12	30	12	112.4	434.1	47 589.2	86.8	98.9
SG-2	12	30	12	87.3	397.5	24 442.7	94.8	98.1
SG-1	18	30	12	124.4	468.3	70 179.5	85.1	99.2
SG-2	18	30	12	97.6	445.8	36 950.7	95.1	98.6
MG-10%	8	30	12	128.4	331.3	30 912.2	94.4	98.5
MG-20%	8	30	12	133.6	358.2	27 098.3	93.2	98.2
MG-30%	8	30	12	115.1	3 197.8	23 289.8	91.7	87.5
MG-30%-2nd	8	30	12	88.3	405.6	22 868.9	90.0	97.9
MG-50%	8	30	12	150.9	5 266.9	16 851.1	93.4	75.7
MG-50%-2nd	8	30	12	73.6	409.4	16 491.9	91.4	97.2
注：样品名中，百分比表示气样中N₂含量，“2nd”表示二次纯化。

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表 3 甲烷不充分回收时同位素组成

Table 3. Isotopic composition of CH₄ in inadequate recovery

气样	体积/mL	采样时间/min	回收率/%	纯度/%	δ¹³C_VPDB/‰
SG-1	6	5	36.3	98.1	-41.52
SG-1	6	10	54.0	98.6	-42.22
SG-1	6	17	69.4	98.4	-42.68
SG-1	6	30	88.6	97.8	-42.89
SG-1	6	40	90.2	98.0	-43.02
SG-1	6	50	94.1	97.5	-43.39
注：SG-1初始同位素组成δ¹³C_VPDB-initial=-43.26‰。

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