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For the precise determination of CF4 in the atmosphere, the uniformly and constantly existing atmospheric krypton (Kr) was used as an internal reference because of its similar properties and behavior to CF4 during the preconcentration processes and GC/MS analysis. The precision of the concentration measurement normalized with a Kr isotope was remarkably improved (to less than 1%) and the sample amount necessary was largely reduced to about one tenth.
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Aoki et al. (2004) studied this question.
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