Biological Chemistry - Berezov T. T., Korovkin B. F. 1998

Vitamins
Methods for Vitamin Determination

Modern Methods for determining Vitamins in biological samples are divided into physicochemical and biological.

When vitamins interact with certain chemical compounds, characteristic color reactions occur, the intensity of which is directly proportional to the vitamin concentration in the test solution. Therefore, Vitamins can be quantified using photocolorimetry—for example, vitamin B₁ with a diazo reagent, and so on. These methods make it possible to assess both the presence of VITAMINS AND THEIR quantitative content in a given food product or in the Organs and Tissues of animals and humans. To evaluate a human body's supply of a particular vitamin, the corresponding vitamin or its metabolite is frequently measured in Blood serum, urine, or biopsy material. However, these methods are not always applicable. Difficulties often arise in selecting a specific reagent to react with a particular vitamin. Certain vitamins have The ability to absorb optical radiation only within a specific region of the spectrum. Specifically, vitamin A exhibits a characteristic absorption band at 328-330 nm. By measuring the absorption coefficient spectrophotometrically, one can determine the quantitative content of vitamins in the test sample with high precision. Fluorometric methods are employed to determine vitamins B₁, B₂, and others. Titrimetric methods are also utilized: for instance, Vitamin C can be quantified by titration with a 2,6-dichlorophenolindophenol solution.

Biological methods are based on determining the minimum amount of a vitamin that, when added to a synthetic diet devoid solely of that specific test vitamin, prevents an animal from developing avitaminosis or cures it of an already manifested deficiency disease. This amount of the vitamin is conventionally defined as a unit (such as "pigeon units" or "rat units" found in the literature). Microbiological methods play a major role in the Quantitative determination of certain vitamins—such as Folic acid, p-aminobenzoic acid, and others—in biological fluids, particularly blood. These methods are based on measuring the bacterial growth rate, which is proportional to the vitamin concentration in the sample. In addition, vitamin content is commonly expressed in milligrams, micrograms, or international units (IU).