diplomsko delo visokošolskega študijskega programa
Matej Kovač (Author), Darinka Brodnjak-Vončina (Mentor), Maša Islamčević Razboršek (Co-mentor)

Abstract

Namen diplomskega dela je bil razvoj analizne metode za določanje izbranih fenolnih kislin (klorogenske in kavne kisline) v ekstraktu zelene kave ob uporabi plinske kromatografije in masne spektrometrije (GC-MS). Ker preiskovane fenolne kisline niso dovolj hlapne in termično obstojne za direktno analizo z GC-MS jih je bilo potrebno predhodno pretvoriti v bolj obstojne in lažje hlapne trimetilsililirane (TMS) derivate . Pred samim sililiranjem je bilo potrebno odstraniti vse sledove polarnih protičnih organskih topil in vode. To smo dosegli z uparevanjem z rotacijskim uparjalnikom do suhega. Kot derivatizacijski reagnet za reakcijo sililiranja smo uporabili trimetilsilil trifluoroacetamid (MSTFA), kot optimalni katalizator pa piridin. Sililiranje smo izvajali na peščeni kopeli, kjer smo vzorce in standardne spojine segrevali pri 80°C 45 minut. Za pripravo raztopin ustrezno nizkih koncentracij smo vzorce in standarde pred nanosom na kolono dodatno rečili s toluenom. Tako smo dobili po GC-MS analizi najustreznejše ločitve in primerne MS spektre preiskovanih spojin. Vsebnosti kavne in klorogenske kisline so bile določene iz odgovarjajočih umeritvenih premic z uporabo vanilinske kisline kot internega standarda (ISTD). Določili smo linearnost metode, natančnost kot ponovljivost, heteroscedastičnost in homoscedastičnost ter ostale parametre, ki so potrebni za validacijo metode. Linearnost metode smo preverjali in potrdili v koncentracijskih območjih od 20 do 200 mg L-1. Korelacijski koeficienti (r2) so bili večji od 0,9942. Dokazali smo, da je metoda ponovljiva (RSD<15%), točna in natančna. S kvantitativno analizo komercialno dosegljivih ekstraktov zrn zelene kave smo določili vsebnosti obeh spojin in sicer kavne kisline 16,1 ± 1,1 mg g-1 suhe zatehte ekstrakta in klorogenske kisline 197,7 ± 13,6 mg g-1 suhe zatehte ekstrakta. Iz rezultatov je razvidno, da prihaja do razlik v deklariranih (450 mg g-1) in z analizo določenih vsebnostih klorogenske kisline. Vzrok za to bi lahko bila nehomogenost vzorca, premalo število odvzetih vzorcev in premalo število neodvisno ponovljenih analiz.

Keywords

kavna kislina;klorogenska kislina;vanilinska kislina;plinska kromatografija;masna spektrometrija;

Data

Language: Slovenian
Year of publishing:
Typology: 2.11 - Undergraduate Thesis
Organization: UM FKKT - Faculty of Chemistry and Chemical Engineering
Publisher: [M. Kovač]
UDC: 543.51.543.544.3(043.2)
COBISS: 18400278 Link will open in a new window
Views: 1984
Downloads: 225
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Other data

Secondary language: English
Secondary title: Simultaneous deterrmination of selected phenolic acids in coffea canephora extract by gas chromatography and mass spectrometry
Secondary abstract: The aim of my thesis was to develop an analytical method for the determination of selected phenolic acids (chlorogenic and caffeic acid) in the green coffee extract using gas chromatography and mass spectrometry (GC-MS). Investigated phenolic acids are not suitable for direct GC-MS analysis because of their high polarity and low volatility therefore they had to be previously converted to more stable and volatile trimethylsilylated (TMS) derivatives. Before the silylation all traces of polar protic organic solvents and water had to be removed. This was achieved by evaporation with a rotary evaporator to complete dryness. N-methyl-N-trimethylsilyl trifluoroacetamide (MSTFA) was used as derivatisation reagent, pyridine was used as the optimum catalyst. Silylation was carried out in a sand bath, where the standard compounds were heated for 45 minutes at 80 °C.. For the preparation of solutions with appropriate concentrations, the samples and standards were diluted with toluene before applying to the column. In this way the most suitable separation and appropriate MS spectra´s of the investigated compounds were achieved. The contents of caffeic and chlorogenic acid were determined from the corresponding calibration curves using vanillic acid as an internal standard (ISTD). We determined the linearity of methods, accuracy, repeatability, heteroscedasticity and homoscedasticity, and other parameters that are required for the validation of the method. Linearity of the method was confirmed in the concentration range from 20 to 200 mg L-1. Correlation coefficients (r2) were greater than 0.9942. It was proved that the method is reproducible (RSD <15%), accurate and precise. By quantitative analysis it was established that the commercially-available dry weighed green coffee beans extract contains in average 16.1 ± 1.1 mg g-1 of caffeic acid and 197.7 ± 13.6 mg g-1 of chlorogenic acid. From the results it is evident that the level of chlorogenic acid was inconsistent with the manufacturer declaration and it was significantly lower than that specified on the packaging (450 mg g-1). The main reasons for such results could be lack of homogeneity of the sample, insufficient number of analysed samples or insufficient number of independently performed analyses.
Secondary keywords: caffeic acid;chlorogenic acid;vanilic acid;gas chromatography;mass spectrometry;
URN: URN:SI:UM:
Type (COBISS): Undergraduate thesis
Thesis comment: Univ. v Mariboru, Fak. za kemijo in kemijsko tehnologijo
Pages: VIII, 42 str.
ID: 8690654