Razvoj in optimizacija spektrofotometrične metode za določanje amonijaka

Zidarič, Nina (avtor), Kolar, Mitja (mentor)

Amonijak je na drugem mestu med kemikalijami proizvedenimi po svetu. Večina svetovne proizvodnje amonijaka – skoraj 70 % – se uporablja kot umetno dušikovo gnojilo, saj je dušik nujno hranilo za zdravo rast rastlin, pridelavo sadja in sintezo klorofila. Za večino svetovnih emisij amonijaka so odgovorne antropogene dejavnosti, med drugim kmetijstvo, kurjenje biomase in energetski sektor. Za določanje amonijaka se najpogosteje uporabljajo kolorimetrične metode (Berthelotove ali Nesslerjeve) ter titracija in ionsko-selektivne elektrode. V sklopu magistrskega dela sem optimizirala spektrofotometrično salicilatno metodo, ki je modifikacija Berthelotove reakcije, kjer fenol nadomestimo z natrijevim salicilatom. Predhodno sem imela določen optimalni pH in vrstni red mešanja reagentov ter katalizatorja. Spreminjala sem koncentracije reagentov in katalizatorja ter za različna razmerja merila absorbanco v odvisnosti od časa. Po določitvi pogojev za najhitrejšo reakcijo – 1 mM natrijev hipoklorit, 20 mM natrijev salicilat in 10 mM natrijev nitroprusid, ki je bil raztopljen v 0,1 M natrijevem hidroksidu (skupna koncentracija NaOH je bila 20 mM) – sem preverila, ali s temi pogoji dobimo linearno umeritveno krivuljo za predvidene koncentracije. Določila sem tudi mejo detekcije (0,19 μM NH3) in vpliv interferenc (najbolj vplivajo amini, predvsem trietilamin, in manganovi(II) ioni). Optimizirane reakcijske pogoje se bo uporabilo za izdelavo amonijevega senzorja za določitev koncentracije amonijaka v pretočnem sistemu. V sklopu magistrskega dela sem razvila še eksperimentalno delo za dijake, pri katerem dijaki spoznavajo in raziskujejo to metodo za določanje amonijaka ter se učijo o kemijski kinetiki (vplivih na hitrost reakcije) in spektrofotometriji. Pri eksperimentalnem delu dobimo s spektrofotometrom bolj ponovljive in točne rezultate, a ga je mogoče izvesti tudi s pametnim telefonom z aplikacijo Barvni detektor.

• Jezik: Slovenski jezik
• Ključne besede: amonijak, Berthelotova reakcija, spektrofotometrija, razmerje reagentov, interference, eksperimentalno delo za dijake
• Vrsta gradiva: Magistrsko delo/naloga
• Organizacija: FKKT - Fakulteta za kemijo in kemijsko tehnologijo
• Leto izida: 2026
• PID: 20.500.12556/RUL-188866
• Datum objave v RUL: 29.09.2026

Sekundarni jezik

• Jezik: Angleški jezik
• Naslov: Development and optimization of a spectrophotometric method for determination of ammonia

Izvleček

Ammonia is the second most produced chemical in the world. Most of the world's ammonia production – almost 70% – is used as an artificial nitrogen fertilizer, as nitrogen is an essential nutrient for healthy plant growth, fruit production and chlorophyll synthesis. Anthropogenic activities, including agriculture, biomass burning and the energy sector, are responsible for most global ammonia emissions. The most used methods for determining ammonia in water are colorimetric methods (Berthelot or Nessler), titration and ion-selective electrodes. As part of my master's thesis, I optimized the spectrophotometric salicylate method, which is a modification of the Berthelot reaction, where phenol is replaced by sodium salicylate. The optimal pH and the order of mixing reagents and catalyst was predetermined. I varied the concentrations of reagents and the catalyst and measured the absorbance as a function of time for different reagent ratios. After determining the conditions for the fastest reaction – 1 mM sodium hypochlorite, 20 mM sodium salicylate, and 10 mM sodium nitroprusside, which was dissolved in 0.1 M sodium hydroxide (total NaOH concentration was 20 mM) – I checked whether these conditions give a linear calibration curve for the intended concentrations. I also determined the detection limit (0.19 μM NH3) and the influence of interferences. Amines (especially triethylamine) and manganese (II) ions, had the greatest influence. The optimized reaction conditions will be used to produce an ammonium sensor for determining the concentration of ammonia in a flow system. As part of my master's thesis, I also developed an experimental learning unit for students in which students learn about and research this method for determining ammonia and learn about chemical kinetics (effects on reaction rate) and spectrophotometry. In the experimental learning unit, we obtain more reproducible and accurate results with a spectrophotometer, but it can also be performed with a smartphone using the Color Detector app.

• Ključne besede: ammonium, Berthelot reaction, spectrophotometry, reagent ratio, interferences, experimental work for students