In this master's thesis, we investigated the performance of a modular system with a flow-through cell and a molecular fluorescence detector. Firstly, we determined the characteristics of the modular fluorescence system. We compared spectrums obtained with modular system with the spectrums obtained with a hybrid molecular fluorescence spectrometer. The results of both instruments were highly comparable. With the modular system we also recorded emission spectra of seven compounds with different absorption and emission maxima. We were able to obtain emission peaks of compounds with absorption maxima above 300 nm and emission maxima above 400 nm. These compounds were salicylic acid, quinine sulfate, fluorescein, riboflavin, and rhodamine B. However, we were not able to detect any emission peaks for benzoic acid and folic acid. After that, we conducted the qualification of the modular fluorescence system. We verified the detector and determined wavelength accuracy, which was satisfactory. For quinine sulfate we determined the linear range from 100 µg/L to 5 mg/L with limit of detection 100 µg/L and for fluorescein from 2,5 µg/L to 1 mg/L with limit of detection 2,5 µg/L. For the same compounds we also checked the repeatability of peak wavelength and intensity. Finally, we evaluated the baseline level and stability. It was higher and less stable for the deuterium lamp in comparison with the halogen lamp. When using the flow-through cell, it was first necessary to investigate the effects on the dispersion coefficients. We varied the coil length, flow rate, and injected investigated solution volume. We found that the dispersion coefficient decreases with increasing investigated solution volume and increases with increasing flow rate with no significant effect of the coil length. Lastly, we demonstrated the use of the modular system on the example of ammonia nitrogen determination in real water sample. Under enough basic conditions NH4+ is quantitatively converted to NH3, consequently all of the ammonia nitrogen was in unionized form NH3. The determination was based on the reaction between ammonia and o-phthaldialdehyde in the presence of a reducing agent, resulting in a fluorescent product. From its emission spectrum, we determined the emission peak at 425 nm when being excited with a deuterium lamp. The optimal conditions chosen for the reaction in the flow system were coil length 100 cm, flow rate 0,2 mL/min, volume of injected investigated solution 0,1 mL and water bath temperature 80 °C. For this method, we determined a linear range from 0,075 mg/L to 5 mg/L with limit of detection 0,075 mg/L. In the sample Boračevski potok, we determined the ammonia nitrogen concentration to be 2,57 mg/L ± 0,13 mg/L and relative standard deviation of 16,5 % with ten measurements being made.
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