Mortazavi Behzad, Chanton Jeffrey P
Department of Oceanography, Florida State University, Tallahassee, FL 32306-4320, USA.
Rapid Commun Mass Spectrom. 2002;16(14):1398-403. doi: 10.1002/rcm.730.
A simple modification to a commercially available gas chromatograph isotope ratio mass spectrometer (GC/IRMS) allows rapid and precise determination of the stable isotopes ((13)C and (18)O) of CO(2) at ambient CO(2) concentrations. A sample loop was inserted downstream of the GC injection port and used to introduce small volumes of air samples into the GC/IRMS. This procedure does not require a cryofocusing step and significantly reduces the analysis time. The precisions for delta(13)C and delta(18)O of CO(2) at ambient concentration were +/-0.164 and +/-0.247 per thousand, respectively. This modified GC/IRMS was used to test the effects of storage on the (18)O and (13)C isotopic ratios of CO(2) at ambient concentrations in four container types. On average, the change in the (13)C-CO(2) and (18)O-CO(2) ratios of samples after one week of storage in glass vials equipped with butyl rubber stoppers (Bellco Glass Inc.) were depleted by 0.12 and by 0.20 per thousand, respectively. The (13)C ratios in aluminum canisters (Scotty II and IV, Scott Specialty Gasses) after one month of storage were depleted, on average, by 0.73 and 2.04 per thousand, respectively, while the (18)O ratios were depleted by 0.38 and 1.20 per thousand for the Scotty II and IV, respectively. After a month of storage in electropolished containers (Summa canisters, Biospheric Research Corporation), the (13)C-CO(2) and (18)O-CO(2) ratios were depleted, on average, by 0.26 and enriched by 0.30 per thousand, respectively, close to the precision of measurements. Samples were collected at a mature hardwood forest for CO(2) concentration determination and isotopic analysis. A comparison of CO(2) concentrations determined with an infrared gas analyzer and from sample voltages, determined on the GC/IRMS concurrent with the isotopic analysis, indicated that CO(2) concentrations can be determined reliably with the GC/IRMS technique. The (13)C and (18)O ratios of nighttime ecosystem-respired CO(2), determined from the intercept of Keeling plots, were -26.11 per thousand (V-PDB) and -8.81 per thousand (V-PDB-CO(2)), respectively.
对市售气相色谱 - 同位素比率质谱仪（GC/IRMS）进行简单改装，可在环境二氧化碳浓度下快速精确测定二氧化碳的稳定同位素（¹³C和¹⁸O）。在气相色谱进样口下游插入一个进样环，用于将少量空气样品引入GC/IRMS。此方法无需低温聚焦步骤，可显著缩短分析时间。环境浓度下二氧化碳δ¹³C和δ¹⁸O的测定精度分别为±0.164‰和±0.247‰。使用这种改装后的GC/IRMS测试了四种容器类型中储存对环境浓度下二氧化碳¹⁸O和¹³C同位素比率的影响。平均而言，在配备丁基橡胶塞（Bellco Glass Inc.）的玻璃瓶中储存一周后，样品的¹³C - 二氧化碳和¹⁸O - 二氧化碳比率分别降低了0.12‰和0.20‰。在铝罐（Scotty II和IV，Scott Specialty Gasses）中储存一个月后，¹³C比率平均分别降低了0.73‰和2.04‰，而Scotty II和IV的¹⁸O比率分别降低了0.38‰和1.20‰。在电解抛光容器（Summa罐，Biospheric Research Corporation）中储存一个月后，¹³C - 二氧化碳和¹⁸O - 二氧化碳比率平均分别降低了0.26‰和升高了0.30‰，接近测量精度。在一片成熟的硬木森林中采集样品用于二氧化碳浓度测定和同位素分析。将用红外气体分析仪测定的二氧化碳浓度与在进行同位素分析的同时在GC/IRMS上测定的样品电压所确定的浓度进行比较，结果表明使用GC/IRMS技术能够可靠地测定二氧化碳浓度。根据基林曲线的截距确定的夜间生态系统呼出二氧化碳的¹³C和¹⁸O比率分别为 - 26.11‰（V - PDB）和 - 8.81‰（V - PDB - 二氧化碳）。
