Flores Edgar, Rhoderick George C, Viallon Joële, Moussay Philippe, Choteau Tiphaine, Gameson Lyn, Guenther Franklin R, Wielgosz Robert Ian
†Bureau International des Poids et Mesures (BIPM), Pavillon de Breteuil, F-92312 Sèvres Cedex, France.
‡Chemical Sciences Division, Material Measurement Laboratory, National Institute of Standards and Technology, 100 Bureau Drive, Gaithersburg, Maryland 20899-8393, United States.
Anal Chem. 2015 Mar 17;87(6):3272-9. doi: 10.1021/ac5043076. Epub 2015 Feb 25.
There is evidence that the use of whole air versus synthetic air can bias measurement results when analyzing atmospheric samples for methane (CH4) and carbon dioxide (CO2). Gas chromatography with flame ionization detection (GC-FID) and wavelength scanned-cavity ring down spectroscopy (WS-CRDS) were used to compare CH4 standards produced with whole air or synthetic air as the matrix over the mole fraction range of 1600-2100 nmol mol(-1). GC-FID measurements were performed by including ratios to a stable control cylinder, obtaining a typical relative standard measurement uncertainty of 0.025%. CRDS measurements were performed using the same protocol and also with no interruption for a limited time period without use of a control cylinder, obtaining relative standard uncertainties of 0.031% and 0.015%, respectively. This measurement procedure was subsequently used for an international comparison, in which three pairs of whole air standards were compared with five pairs of synthetic air standards (two each from eight different laboratories). The variation from the reference value for the whole air standards was determined to be 2.07 nmol mol(-1) (average standard deviation) and that of synthetic air standards was 1.37 nmol mol(-1) (average standard deviation). All but one standard agreed with the reference value within the stated uncertainty. No significant difference in performance was observed between standards made from synthetic air or whole air, and the accuracy of both types of standards was limited only by the ability to measure trace CH4 levels in the matrix gases used to produce the standards.
有证据表明，在分析大气样本中的甲烷（CH4）和二氧化碳（CO2）时，使用全空气与合成空气会使测量结果产生偏差。采用带有火焰离子化检测的气相色谱法（GC-FID）和波长扫描腔衰荡光谱法（WS-CRDS），在1600 - 2100 nmol mol(-1)的摩尔分数范围内，比较以全空气或合成空气为基质产生的CH4标准气体。GC-FID测量通过加入与稳定对照气瓶的比率来进行，获得的典型相对标准测量不确定度为0.025%。CRDS测量采用相同的方案，并且在不使用对照气瓶的情况下在有限时间段内不间断进行，分别获得相对标准不确定度为0.031%和0.015%。此测量程序随后用于一项国际比对，其中将三对全空气标准气体与五对合成空气标准气体进行了比较（八家不同实验室各提供两对）。全空气标准气体相对于参考值的变化确定为2.07 nmol mol(-1)（平均标准偏差），合成空气标准气体的变化为1.37 nmol mol(-1)（平均标准偏差）。除一个标准气体外，所有标准气体均在规定的不确定度范围内与参考值相符。未观察到由合成空气或全空气制成的标准气体在性能上有显著差异，并且这两种标准气体的准确度仅受用于制备标准气体的基质气体中痕量CH4水平测量能力的限制。
