A Study on High Sensitivity Mass Spectrometry of Stable Carbon Isotopes

稳定碳同位素高灵敏度质谱研究

• 批准号: 04554024
• 负责人: SUGIURA Naoji
• 金额: $ 7.36万
• 依托单位: The University of Tokyo
• 依托单位国家: 日本
• 项目类别: Grant-in-Aid for Developmental Scientific Research (B)
• 财政年份: 1992
• 资助国家: 日本
• 起止时间: 1992 至 1993
• 项目状态: 已结题
• 来源: https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-04554024/
• 关键词: Carbon Isotopes; carcondioxide; mass spectrometry; QMS; 真空システム; 段階加熱; 窒素; 希ガス

We are constructing a vacuum system equipped with a quadrupole-type mass spectrometer (MSQ400, ULVAC Co., Japan) for analyzing isotopic composition of nano-mole carbon in a static mode.We analyze carbon isotopes as carbondioxide and measure mass 42,44,45 and 46. Peaks are electrically scanned and 10 sets of data are obtained in 160 seconds. Carbondioxide tends to decompose partly into CO and partly into C to form possibly metal-carbide during the analysis due to interaction between gas and hot filament. In order to minimize this effect, we replace first a tungsten filament with a yttria (Y_2O_3) -coated iridium filament which has lower work function. This lengthen the "half life" of CO_2 in the mass spectrometer by a factor of about 5. Secondly, we lower the emission current from 1.0 mA to 0.1 mA.In this condition, the "half life" of CO_2 becomes longer than 120 sec. The ion source we are using is an "open-type" (Prosser et al., 1990) However, the observed "half life" of CO_2 is much longer than that for other "open sources" (-35 sec, Carr et al., 1986) and only a factor of three shorter than that for the "closed source" (-450 sec, Prosser et al., 1990). We found more than 80% of the gas existed as CO_2 even at the end of the analysis.At present, the^<13>C/^<12>C ratios observed for repeated analyzes of a standard gas (about 1 nano-mole CO_2 ) are reproducible within <plus-minus>0.5%. However, there seems to be some pressure dependence in the discrimination factor for ^<12>C and ^<13>C.The lower limit of the sample size for carbon isotope analysis with this system is about 0.1 nano-mole.

我们正在构建一个配备四极型质谱仪（MSQ400，ULVAC Co，日本）的真空系统，用于在静态模式下分析纳米摩尔碳的同位素组成。我们将碳同位素分析为二氧化碳，并测量质量42、44、45和46。对峰进行电扫描，并在160秒内获得10组数据。由于气体和热灯丝之间的相互作用，在分析过程中二氧化碳往往会部分分解为 CO，部分分解为 C，从而可能形成金属碳化物。为了最大限度地减少这种影响，我们首先用逸出功较低的氧化钇 (Y_2O_3) 涂层铱丝代替钨丝。这使得质谱仪中CO_2的“半衰期”延长了约5倍。其次，我们将发射电流从1.0 mA降低到0.1 mA。在这种情况下，CO_2的“半衰期”变得超过120秒。我们使用的离子源是“开放式”离子源（Prosser et al., 1990）。然而，观察到的 CO_2 的“半衰期”比其他“开放源”（-35 秒，Carr et al., 1986）长得多，仅比“封闭源”（-450 秒，Prosser et al., 1990）短三倍。即使在分析结束时，我们也发现超过80%的气体以CO_2的形式存在。目前，对标准气体（约1纳摩尔CO_2）进行重复分析所观察到的^<13>C/^<12>C比率可在<正负>0.5%内重现。然而，^ 12 C和^ 13 C的辨别因子似乎存在一些压力依赖性。用该系统进行碳同位素分析的样品尺寸的下限为约0.1纳摩尔。