| Abstract | Limunska kiselina se u farmaceutskoj i prehrambenoj industriji koristi kao antioksidans i regulator kiselosti, a
u većim koncentracijama može biti štetna za ljudsko zdravlje. U ovom diplomskom radu određena je koncentracija
limunske kiseline u uzorcima prirodnih i komercijalo dostupnih voćnih sokova. Za određivanje limunske kiseline
korištena je tekućinska kromatografija visoke djelotvornosti (HPLC, Knauer, Berlin, Njemačka) s UV/Vis detektorom,
uz kolonu obrnute faze ( LiChrospher RP-18, 125 x 4,6 mm, 5 μm Merck, Darmstadt, Njemačka). Mobilna faza je bila
50 mM fosfatni pufer (pH = 2,8) s protokom 0,5 mL/min, a valna duljina detektora bila je podešena na 214 nm.
Metoda je ispitana standardnim otopinama limunske kiseline u koncentracijskom rasponu od 0,1 do 1,0 g/L. U
ispitivanom području metoda je bila linearna (koeficijent korelacije, R2 = 0,9999). Ponovljivost metode, izražena kao
relativna standardna devijacija (RSD) bila je ispod 2,5%, a srednja preciznost izražena kao relativna standardna
devijacija (RSD) iznosila je manje od 3%. Granica dokazivanja bila je 0,01 g/L, a granica određivanja 0,03 g/L što
pokazuje da je metoda osjetljiva za određivanje koncentracije limunske kiseline u voćnim sokovima.. Koncentracija
limunske kiseline u šest komercijalno pribavljenih voćnih sokova bila je u rasponu od 1,42 g/L (uzorak 1) do 4,42 g/L
(uzorak 4). Izmjerene koncentracije u devet uzoraka prirodnih voćnih sokova iznosile su od 0 g/L (uzorak 1, 2, 4 i 5)
do 7,66 g/L (uzorak 6). Iz dobivenih rezultata može se zaključiti da je HPLC metoda brza, pouzdana i precizna za
određivanje koncentracije limunske kiseline u uzorcima voćnih sokova. Budući da je u sedam uzoraka, koncentracija
limunske kiseline prelazila propisima dozvoljenu vrijednost, važno je pratiti njenu koncentraciju u svim prehrambenim
proizvodima. |
| Abstract (english) | Citric acid is used in the pharmaceutical and food industries as an antioxidant and acid regulator, but at the
higher concentrations can be harmful to human health. The concentration of citric acid in samples of natural and
commercially available fruit juices is determined in this thesis. High performance liquid chromatography (HPLC,
Knauer, Berlin, Germany) with UV / Vis detector together with a reversed phase column (LiChrospher RP-18, 125 x
4.6 mm, 5 μm Merck, Darmstadt, Germany) was used for the determination of citric acid. The mobile phase was 50
mM phosphate buffer (pH = 2.8) with a flow rate of 0.5 mL/min, and the detector wavelength was adjusted to 214 nm.
The method was tested with standard citric acid solutions in a concentration range of 0.1 to 1.0 g/L. In the study area,
the method was linear (correlation coefficient, R2 = 0.9999). The repeatability of the method, expressed as relative
standard deviation (RSD) was below 2.5%, and the intermediate precision expressed as relative standard deviation
(RSD) was less than 3%.The limit of detection was 0.01 g/L and the limit of quantification was 0.03 g/L indicating
that the method is sensitive to the determination of citric acid concentration in fruit juices. The citric acid
concentration in the six commercially obtained fruit juices ranged from 1.42 g/L (sample 1) to 4.42 g/L (sample 4).
The measured concentrations in nine samples of natural fruit juices ranged from 0 g/L (sample 1, 2, 4 and 5) to 7.66
g/L (sample 6). From the obtained results, it can be concluded that the HPLC method is fast, reliable and accurate for
the determination of citric acid concentration in fruit juice samples. Considering that the concentration of citric acid in
seven samples exceeded the regulatory limit, it is important to monitor its concentration in all food products. |
