Obnašanje modularnega sistema s pretočno celico in fluorescenčnim detektorjem

Šadl, Sara (avtor), Gros, Nataša (mentor)

Pri magistrskem delu smo raziskali obnašanje modularnega sistema s pretočno celico in fluorescenčnim detektorjem. Najprej smo določili lastnosti modularnega fluorescenčnega sistema. Primerjali smo spektre kinin sulfata in rodamina B posnete z modularnim sistemom in s hibridnim molekularnim fluorescenčnim spektrometrom. Rezultati obeh instrumentov so se odlično ujemali. Z modularnim fluorescenčnim sistemom smo tudi posneli emisijske spektre sedmih spojin z različnimi valovnimi dolžinami absorpcijskih in emisijskih maksimumov. Uspeli smo pridobiti emisijske vrhove spojin z absorpcijskimi maksimumi nad 300 nm in emisijskimi maksimumi nad 400 nm. To so bile spojine salicilna kislina, kinin sulfat, fluorescein, riboflavin in rodamin B. Za benzojsko in folno kislino ni bilo možno določiti nobenega emisijskega vrha. Nato smo izvedli kvalifikacijo modularnega fluorescenčnega sistema. Detektor smo verificirali in preverili točnost valovnih dolžini, ki je bila ustrezna. Za kinin sulfat smo določili območje linearnosti od 100 µg/L do 5 mg/L z mejo detekcije 100 µg/L, za fluorescein pa od 2,5 µg/L do 1 mg/L z mejo detekcije 2,5 µg/L. Na istih spojinah smo prav tako preverili ponovljivost valovnih dolžin in intenzitet vrhov. Na koncu smo še ocenili višino in časovno stabilnost bazne linije. Ta je bila višja in je bolj nihala v primeru devterijeve žarnice v primerjavi s halogensko žarnico. Pri uvedbi pretočne celice je bilo najprej potrebno določiti disperzijske koeficiente in raziskati vplive nanj. Spreminjali smo dolžino tuljave, pretok in volumen injicirane preiskovane raztopine. Ugotovili smo, da disperzijski koeficient pada z večanjem volumna injicirane preiskovane raztopine in narašča z večanjem pretoka, dolžina tuljave pa nima izrazitega vpliva. Skladno s tem smo nazadnje prikazali uporabnost sistema na primeru določitve amoniakalnega dušika v realnem vzorcu vode. V dovolj bazičnem mediju se NH$_4^+$ kvantitativno pretvori v NH$_3$, torej se je ves amoniakalni dušik nahajal v neionizirani obliki NH$_3$. Tako je določitev temeljila na reakciji amonijaka z o-ftaldialdehidom ob prisotnosti reducenta, kjer je nastal fluorescenčni produkt. Iz njegovega emisijskega spektra smo odčitali emisijski vrh pri 425 nm ob vzbujanju z devterijevo žarnico. Pogoji, ki smo jih izbrali kot optimalne za izvedbo reakcije s pretočnim sistemom, so bili dolžina tuljave 100 cm, pretok 0,2 mL/min, volumen injicirane preiskovane raztopine 0,1 mL in temperatura vodne kopeli 80 °C. Pri teh vrednostih smo za izbrano metodo določitve koncentracije amoniakalnega dušika s pretvorbo do amonijaka v bazičnem mediju določili območje linearnosti od 0,075 mg/L do 5 mg/L z mejo detekcije 0,075 mg/L. V vzorcu Boračevskega potoka smo določili koncentracijo amoniakalnega dušika 2,57 mg/L ± 0,13 mg/L z relativnim standardnim odmikom 16,5 % pri desetih opravljenih meritvah.

• Jezik: Slovenski jezik
• Ključne besede: pretočna injekcijska analiza, molekularna fluorescenčna detekcija, modularni instrument, amoniakalni dušik, o-ftaldialdehid
• Vrsta gradiva: Magistrsko delo/naloga
• Tipologija: 2.09 - Magistrsko delo
• Organizacija: FKKT - Fakulteta za kemijo in kemijsko tehnologijo
• Leto izida: 2024
• PID: 20.500.12556/RUL-158972
• COBISS.SI-ID: 202750467
• Datum objave v RUL: 24.06.2024

Sekundarni jezik

• Jezik: Angleški jezik
• Naslov: Performance of a modular system with a flow-through cell and a molecular fluorescence detector

Izvleček

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 NH$_4^+$ is quantitatively converted to NH$_3$, consequently all of the ammonia nitrogen was in unionized form NH$_3$. 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.

• Ključne besede: Flow injection analysis, molecular fluorescence detection, modular instrument, ammonia nitrogen, o-phthaldialdehyde