Standard Infrared Absorption Spectrum of Betaine and Optimal Conditions for its Measurement

摘要

赤外線吸収（IR）スペクトルは，しばしば食品添加物の確認試験にその標準参照スペクトルとともに用いられる．ベタインについては，多くの異なるIRスペクトルが報告され，そのため，再現性のある標準IRスペクトルの確立が望まれている．そこで，標準IRスペクトルを得るための測定条件，例えば前処理，測定法や測定技術について検討した．その結果，ベタインの測定に通常用いられるKBr法は，測定室の湿度の影響を受け，しかもベタインとKBrとの間には相互作用があることを明らかにした．最終的には，五酸化リンを用いて，105℃，3時間乾燥したべタインを，流動パラフィン（Nujol）を用いるペースト法でIRスペクトルを測定すれば，再現性のある標準スペクトルが得られることが分かった．%The infrared absorption (IR) spectrum is often used as a standard reference in identification tests of food additives in Japan. In the case of betaine, many different IR spectra have been reported and, therefore, it is necessary to establish an IR spectrum that is reproducible and reliable enough to be used as a standard for identification. In the present study, suitable conditions to obtain a standard IR spectrum were examined from various viewpoints, including pretreatment, selection of method, and measuring technique. The KBr disk method, which has generally been used to identify betaine, was found to be humidity-dependent, and there was also an interaction between betaine and KBr. A reproducible IR spectrum suitable as a standard could be obtained by drying betaine at 105℃ for 3 hours over phosphorus pentoxide, and then measuring the IR spectrum by the liquid paraffin (Nujol) paste method.