1.

2014-07-15

A modified procedure for gas-source isotope ratio mass spectrometry: the long-integration dual-inlet (LIDI) methodology and implications for clumped isotope measurements

Liping Zhou, et al.

Abstract:

High-precision stable isotope measurements in gas-source isotope ratio mass spectrometry are generally carried out by repeated comparison of the composition of an unknown sample with that of a working gas (WG) through a dual-inlet (DI). Due to the established DI protocols, however, most of the sample gas is wasted rather than measured, which is a major problem when sample size is limited. Here we propose a new methodology allowing the measurement of a much larger portion of the available sample. We tested a new measurement protocol, the long-integration dual-inlet (LIDI) method, which consists of a single measurement of the sample for 200 to 60065seconds followed by a single measurement of the WG. The isotope ratios of the sample are calculated by comparison of the beam ratios of the WG and sample at equivalent intensities of the major ion beam. Three isotopically very different CO2 samples were analyzed. The LIDI measurements of large samples (50 to 1006508mol of CO2) measured at quasi-constant beam sizes, and of small samples (1.5 to 26508mol of CO2) measured in micro-volume mode, generated results that are indistinguishable from the standard DI measurements for carbon, oxygen and clumped isotope compositions. The external precision of Δ47 using the LIDI protocol (-±0.007‰) is similar to that of the state of the art DI measurements. For traditional and clumped isotope measurements of CO2, the LIDI protocol allows the measurement of a much larger portion of the sample gas rather than only ~20% of it. In addition, the sample can be measured at higher signal intensity and for longer time, allowing the measurement of smaller samples while preserving precision. We suggest that other gases commonly used for stable isotope measurements with gas-source mass spectrometry would also benefit from this new protocol.

Reference:

Hu B, Radke J, Schlüter H J, et al. A modified procedure for gas‐source isotope ratio mass spectrometry: the long‐integration dual‐inlet (LIDI) methodology and implications for clumped isotope measurements[J]. Rapid Communications in Mass Spectrometry, 2014, 28(13): 1413-1425.

2.

2014-07-10

鄂霍次克海叶绿素浓度反演及其与海冰的关系

周力平 等

Abstract:

通过MODIS卫星遥感数据，本文提取了鄂霍次克海2005-2009年叶绿素含量的时空分布并分析季节性海冰覆盖对其的影响。结果显示，有海冰覆盖的大陆架边缘叶绿素含量明显高于其他区域，随着海冰融化，叶绿素含量逐渐增加，最大值一般出现在5——6月，当融化的海冰面积达到最大面积的88%时，发生春季首次爆发。从叶绿素的空间分布及时间变化可看出，海冰是影响叶绿素含量春季变化的关键因素。

Reference:

刘雪萍, 周力平, 马丹. 鄂霍次克海叶绿素浓度反演及其与海冰的关系[J]. 第十八届中国环境遥感应用技术论坛论文集, 2014.

3.

2014-04-11

Rapid sample preparation of dissolved inorganic carbon in natural waters using a headspace-extraction approach for radiocarbon analysis by accelerator mass spectrometry

Liping Zhou, et al.

Abstract:

We have established a high-throughput headspace-extraction method for the preparation of dissolved inorganic carbon (DIC) from water samples for radiocarbon (14 C) analysis by accelerator mass spectrometry (AMS). Readily available septum-sealed screw cap vials were used for sample processing. Headspace-equilibrated gases with sample CO 2 were transferred using a syringe and cryogenically purified on a vacuum line for graphitization and 14 C-AMS measurements in the Keck Carbon Cycle AMS facility at the University of California, Irvine (KCCAMS/UCI). Systematic investigations have shown that the extraction process does not introduce contaminants that could bias the 14 C measurements and that the 14 C results for standards are consistent with their consensus values. Large numbers of duplicate measurements have established a precision of 1.7‰ for modern samples with an average background of 43,400 radiocarbon year for graphite target samples > 0.3 mg carbon. Seawater samples collected from Newport Beach, California, and processed using the headspace-extraction method yielded 14 C results in excellent agreement with published values obtained with conventional DIC stripping (≤ 2σ). The simplicity of our headspace-extraction approach allows its easy adaptation/implementation to any isotope lab, as we demonstrate here by a series of tests carried out at Peking University, China (PKU). With this innovative method, just 30 mL seawater per sample is needed. Coupled with the sealed tube zinc reduction method, 15 water samples can be prepared and graphitized in 1 day.

Reference:

Gao P, Xu X, Zhou L, et al. Rapid sample preparation of dissolved inorganic carbon in natural waters using a headspace‐extraction approach for radiocarbon analysis by accelerator mass spectrometry[J]. Limnology and Oceanography: Methods, 2014, 12(4): 174-190.