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维生素C是含于各种植物、食品及饮料中的重要营养物质。因此,测定样品中维生素C的含量具有重要意义。关于维生素C的测定方法已报道的有靛酚滴定法,I_2滴定法,N—溴丁二酰亚胺滴定法。这些方法只适于测定常量组分,对微量组分则无能为力。笔者用I_3~-作显色剂,以吸光光度法测定饮料中维生素C。不必对试样进行分离。且对有色、无色、澄清、浑浊试液都可直接测定,并获得满意结果。 1 测定原理本法是利用Vc即使在10~(-5)mol·L~(-1)含量以下的乙酸介质中也能与I_2反应的性质: C_6H_8O_6+I_2=C_6H_6O_6+2HI (Vc)脱氢Vc将Vc与一定过量I_2反应。未反应的I_2与I~-生成显色物质I_3~-配离子:I_2+I~-=I_3~-然后通过I_3~-吸光度,反推出Vc吸光度进而测定Vc含量,Vc检出限为1.2×10~(-4)mol·L~(-1)。
Vitamin C is contained in a variety of plants, food and beverages in the important nutrients. Therefore, the determination of vitamin C content in the sample is of great significance. Methods for the determination of vitamin C have been reported indophenol titration, I_2 titration, N-bromosuccinimide titration. These methods are only suitable for the determination of constant components, the power of micro-components. The author used I_3 ~ - as a developer to absorb the vitamin C in beverages. It is not necessary to separate the sample. And colored, colorless, clear, turbid test solution can be directly measured, and obtain satisfactory results. 1 Determination of the principle This method is the use of Vc even in the 10 ~ (-5) mol·L -1 (acetic acid) below the acetate medium with I 2 reaction properties: C_6H_8O_6 + I_2 = C_6H_6O_6 + 2HI (Vc) dehydrogenation Vc Vc with a certain excess I2 reaction. The unreacted I_2 and I ~ generate the chromogenic substance I_3 ~ - ion: I_2 + I ~ - = I_3 ~ - and then I_3 ~ - absorbance, inverse Vc Vc absorbance was measured, the Vc detection limit was 1.2 × 10 ~ (-4) mol·L -1.