Threshold dilution factor

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[Evaluation of malodor]
Although instrumental analysis methods that capture specific substance concentrations are used to evaluate odors, the number of odorous substances is very large, and analysis and quantification is extremely difficult, especially when many types are mixed together. For this reason, sensory measurement methods using human olfaction (organoleptic measurement methods) are ultimately the basis, and psychophysical evaluation methods based on Weber's law, such as the multiple of the substance's threshold concentration (the concentration at which 50% of people can detect or recognize it), or the threshold dilution multiple (also called odor concentration) required to sense the odor as odorless, as well as odor intensity and unpleasantness sensory scale indications (0 is odorless, 1 is detectable, 2 is recognized, 3 is easily detected, 4 is strong, and 5 is unbearable), are used along with quality judgments. Actual sensory measurements are being made using the three-point comparison odor bag method, in which a polyester bag is filled with odorless air, and then the subject is asked to judge whether or not there is an odor by injecting the sample with a syringe until a specified concentration is reached; the cyclo-factor method, which uses a device that eliminates the effects of temperature and humidity of the measurement sample and can change the dilution factor continuously or stepwise; and the syringe method, which uses a syringe to push the sample gas in front of the nostrils and determine the dilution rate at which half of the subjects can detect the odor. These methods are becoming increasingly popular as practical evaluation methods.

*Some of the terminology that refers to "threshold dilution factor" is listed below.

Source | Heibonsha World Encyclopedia 2nd Edition | Information

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［悪臭の評価］
　悪臭の評価には特定の物質濃度でとらえる機器分析法も用いられるが，においを呈する物質の数が非常に多く，とくに多種が混在している場合の分析，定量はきわめて困難である。このため結局は，人間の嗅覚による感覚測定法(官能測定法)が基本となり，物質の閾（いき）濃度(50％の人が検知，または認知する濃度)に対する倍数，あるいはその臭気が無臭に感じられるまでに要する閾希釈倍数(臭気濃度とも呼ぶ)，さらには臭気強度，不快度の感覚尺度表示(0は無臭，1は検知，2は認知，3は楽に感知，4は強い，5は耐えられない)などウェーバーの法則に基づく精神物理学的評価法が質の判定とともに採用される。実際の感覚測定は，ポリエステル製の袋に無臭空気を満たした後，所定の濃度になるまで試料を注射器で注入して被験者ににおいの有無を判定させる三点比較臭袋（においぶくろ）法，測定試料の温度，湿度による影響を排除し，連続的または段階的に希釈倍数が変えられる装置を用いるサイクロオルファクター法，注射器を利用して試料ガスを鼻孔の前に押し出して被験者の半数がにおいを感ずる希釈率を求める注射器法が利用され，現実的評価法として普及しつつある。…

※「閾希釈倍数」について言及している用語解説の一部を掲載しています。

出典｜株式会社平凡社世界大百科事典 第２版について | 情報