定义Definition
斐林试剂由甲液（硫酸铜溶液）和乙液（酒石酸钾钠的氢氧化钠溶液）临用时等体积混合而成，呈深蓝色。脂肪醛和还原糖加热时把 Cu²⁺ 还原为砖红色 Cu₂O 沉淀；芳香醛和酮一般不反应。
Fehling's solution is made just before use by mixing equal volumes of solution A (copper(II) sulfate) and solution B (potassium sodium tartrate in sodium hydroxide), giving a deep-blue liquid. On heating, aliphatic aldehydes and reducing sugars reduce Cu²⁺ to brick-red Cu₂O; aromatic aldehydes and ketones generally do not react.
原理Principle
酒石酸根与 Cu²⁺ 形成深蓝色配合物，防止碱性条件下 Cu(OH)₂ 沉淀。醛被氧化为羧酸盐，Cu(II) 被还原为 Cu(I) 并以 Cu₂O 析出。
Tartrate forms a deep-blue complex with Cu²⁺, preventing Cu(OH)₂ from precipitating in base. The aldehyde is oxidised to a carboxylate and Cu(II) is reduced to Cu(I), precipitating as Cu₂O.
由来Origin
德国化学家赫尔曼·冯·斐林于 1849 年提出，最初用于测定尿中的糖。由于混合后的试剂不稳定，需分成两液保存。
Introduced by the German chemist Hermann von Fehling in 1849, originally to determine sugar in urine. Because the mixed reagent is unstable, it is stored as two separate solutions.
用途Uses
可区分脂肪醛与芳香醛、醛与酮，并可用于还原糖的定量（如雷因-艾农法测定乳糖、葡萄糖）。中学生物实验常用于检测还原糖。
It distinguishes aliphatic from aromatic aldehydes and aldehydes from ketones, and is used quantitatively for reducing sugars (e.g. the Lane–Eynon method). School biology uses it to detect reducing sugars.
反应Reactions
甲、乙液等体积现混，与样品共热至沸
Mix A and B in equal volumes just before use and boil with the sample
混合甲乙液得到酒石酸铜配合物。
Mixing gives the copper–tartrate complex.
加热时醛基被氧化。
On heating the aldehyde is oxidised.
生成砖红色 Cu₂O 沉淀。
Brick-red Cu₂O precipitates.
乙醛阳性；苯甲醛阴性。
Acetaldehyde is positive; benzaldehyde is negative.
年表Timeline
- 1849
斐林发表该试剂
Fehling publishes the reagent
- 1923
雷因与艾农建立斐林滴定法测糖
Lane and Eynon develop the Fehling titration for sugars