The assessment methods of chlorophyll «а» in the natural waters have been analyzed. This pigment of phytoplankton is the main indicator of the primary bioproductivity and trophicity of the reservoir. The key spectrometric methods of determination were compared, and their advantages and disadvantages were Аналитика и контроль. 2019. Т. 23. № 3. discussed. The application features of different types of spectrometric determination of the analyte from classical spectrophotometric methods to remote

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... ensing of water bodies were considered. The preference was shown for the determination of chlorophyll by the fluorescent methods, which were used in different implementation variations. The method of extraction-fluorescent determination of chlorophyll «а» was substantiated and implemented after the chlorophyll extraction from the water with chloroform and measuring the fluorescence intensity at λ exc = 418 nm and λ lum = 675 nm. The results of the chlorophyll «а» determination were compared using the standardized spectrophotometric and the developed techniques for the model and real water samples. It was educed that in the area of low concentrations of chlorophyll «а» (0.05 μg of analyte in 1000 cm 3 of water) the analytical signal was recorded only by the fluorimetric method, while in the area of higher concentrations (0.2 μg of analyte in 1000 cm 3 of water) the standardized spectrophotometric method produced the overestimated results. The developed method for the extraction-fluorimetric determination of chlorophyll «а» in the natural waters (both fresh and marine) was metrologically certified and put into the register of the Federal Information Fund for ensuring the uniformity of measurements.