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External standard method

  • The external standard method includes construction of a calibration curve. For calibration curve, certain volumes of standard solutions are injected, and the concentrations of those solutions are known. Curve is constructed based on the responses of each concentration, and the concentrations of the samples are determined by comparing the responses of the samples to the calibration curve.


  • Vitamin fortification is a process where vitamins are added to food. These added vitamins may replace vitamin losses caused by processing, or vitamins may be added in order to prevent vitamin deficiency among population.


  • In microbiological assays the growth medium is inoculated with the selected microbe. The growth medium must contain all the nutrients needed for the growth of the microbe except the analyte itself. The growth medium with the microbe is then injected to the sample solution, and the growth of the microbe is dependent on the amount of the analyte in the sample.  

Internal standard method

  • In the internal standard method, a certain amount of standard substance is added to the samples. The concentration of the analyte in the sample is determined by comparing the response of the analyte in the sample to the response of the added standard substance. The standard substance should be selected so that it would not elute simultaneously with any of the compounds found in the sample solutions but would still be sufficiently similar to the analyte. The ratio of the analyte to the standard substance remains the same in spite of some changes in measurement environment and possible errors during sample treatment (e.g. spilling of the sample solution), and thus this kind of things do not affect the results.


  • Isomers are compounds with the same molecular formula but different structures. Isomers can have different kind of functional groups and thus have dissimilar properties.  Isomerism can be divided to structural isomerism and stereoisomerism.


  • Provitamin is a compound that is converted to an actual vitamin form after consumption in the body. Provitamins are thus precursors of the vitamin - e.g. carotenoids are precursors of vitamin A.


  • Vitamers are compounds that have same kind of vitamin activity. For example vitamers of niacin include niacin (=nicotinic acid) and niacinamide (=nicotinamide).