magistrsko delo
Saša Pušaver (Author), Matjaž Finšgar (Mentor), Maša Islamčević Razboršek (Co-mentor)

Abstract

V tem delu smo razvili metodo za določevanje posameznih monosaharidov s plinsko kromatografijo in masno spektrometrijo (GC-MS). V vzorcu hemiceluloze smo določali štiri enostavne sladkorje, in sicer D-glukozo, L-arabinozo, D-ksilozo in L-ramnozo. Ker monosaharidi niso hlapne spojine, smo jih s pomočjo derivatizacije oz. sililiranja pretvorili v lažje hlapne spojine. Kot sililirno sredstvo smo uporabljali MSTFA (N-metil-N-trimetilsilil trifluoroacetamid), kot katalizator pa sušen piridin. Reakcijo sililiranja smo izvajali 60 minut pri temperaturi 80 °C. Posamezne vrhove smo identificirali tako, da smo vselej primerjali retencijske čase in masne spektre posameznih monosaharidov v vzorcih z retencijskimi časi in masnimi spektri standardnih spojin, posnetih pri enakih eksperimentalnih pogojih ali s pomočjo masnih spektrov iz knjižnice (Wiley, NIST) masnih spektrov. Fenil β-D-glukopiranozid smo uporabili kot interni standard (ISTD). Pridobljene rezultate smo statistično ovrednotili in dokazali, da je metoda ponovljiva ter natančnost metode z RSD<20%. Linearnost smo preverjali v koncentracijskih območjih od 20 pa vse do 200 mg/L. Metoda je linearna, s korelacijskimi koeficienti med 0,9934 in 0,9995. Vzorec hemiceluloze smo ekstrahirali z metanolizo. Vzorec smo raztopili v metanolu z dodatkom HCl (2 M ali 5 M) ali H2SO4 (2 M ali 5 M). Vzorec smo ekstrahirali 3,5 ure pri temperaturi 100 °C. V vseh vzorcih smo od preiskovanih analitov zaznali in določili le glukozo, ostalih monosaharidov (arabinozo, ksilozo in ramnozo) nismo identificirali. Iz rezultatov smo ugotovili, da je največ glukoze (povprečno 340,9 mg/g hemiceluloze) v vzorcu ekstrakta hemiceluloze, ekstrahiranem s 5 M HCl v metanolu pri 100 °C 3,5 ure. Nižjo vsebnost glukoze (povprečno 201,8 mg/g hemiceluloze) pa smo določili v vzorcu hemiceluloze, ekstrahiranem z 2 M HCl v metanolu pri 100 °C 3,5 ure. Pri naših eksperimentih se je pokazalo, da H2SO4 v metanolu (2 M, 5 M) ni najbolj primeren medij za uporabo pri hidrolizi vzorcev hemiceluloze. Že med samo ekstrakcijo so vzorci potemneli, nekatere smo uspeli analizirati, vendar iz kromatogramov sklepamo, da je prišlo do razgradnje vzorca med samo ekstrakcijo. Čeprav je v znanstveni literaturi zaslediti uporabo H2SO4 pri hidrolizi, bi bilo potrebno narediti dodatne eksperimente in metodo bolje optimirati.

Keywords

hemiceluloza;monosaharidi;plinska kromatografija;masna spektrometrija;derivatizacija;magistrske naloge;

Data

Language: Slovenian
Year of publishing:
Typology: 2.09 - Master's Thesis
Organization: UM FKKT - Faculty of Chemistry and Chemical Engineering
Publisher: [S. Pušaver]
UDC: 543.544.3:543.51(043.2)
COBISS: 19528726 Link will open in a new window
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Other data

Secondary language: English
Secondary title: DETERMINATION OF DIFFERENT MONO-SACCHARIDES IN SELECTED EXOPOLYSACCHARIDES USING GAS CHROMATOGRAPHY AND MASS SPECTROMETRY
Secondary abstract: A gas chromatographic – mass spectrometric (GC-MS) method for the simultaneous separation, identification and determination of monosaccharides glucose, arabinose, xylose, and rhamnose in wood hemicellulose samples has been developed. Hydrolysis/methanolysis of the hemicellulose samples was performed by 2 M HCl/MeOH or 5 M HCl/MeOH or 2 M H2SO4/MeOH or 5 M H2SO4/MeOH in flasks, equipped with a condenser. The water bath temperature was maintained at 100 °C for 3.5 hours. The resulting monosaccharide units were trimethylsilylated (TMS) using MSTFA (N-methyl-N-(trimethylsilyl)trifluoroacetamide) as derivatization reagent and dry pyridine by heating for 60 min at 80 °C. The compounds were identified and quantified by comparison of their retention times in gas chromatograms and EI mass spectras with those of pure standards or by comparing their spectral properties with those reported in the Wiley and Nist computer libraries. Phenyl β-D-glucopyranoside was used as an internal standard (ISTD). The linearity of the method was tested within the concentration range 20−200 mg L-1. Method was linear with the correlation coefficients (r2) in the range of 0.9934 to 0.9995. It was also proved that the method is repeatable (precise) (RSD<20%), and accurate. Arabinose, xylose and rhamnose were not identified in the samples. The results confirmed that the highest concentration of glucose (in average 340.9 mg/g hemicellulose) was present in the sample where hemicellulose was methanolysed with 5 M HCl/MeOH and boiling for 3.5 h at 100 °C. Relatively high concentration of glucose (in average 201.8 mg/g hemicellulose) was determined in the hydrolysate prepared with 2 M HCl/MeOH. In our experiments, it was shown that H2SO4 in methanol (2 M, 5 M) was not the most appropriate medium for use in the hydrolysis of hemicellulose samples. During the extraction, samples became darker, and from the chromatograms we concluded that the samples degradated already during the extraction. Although in the scientific literature H2SO4 has been used in in the hydrolysis of hemicellulose, further experiments should be performed and the method should be better optimized.
Secondary keywords: hemicellulose;monosaccharides;gas chromatography;mass spectrometry;derivatization;
URN: URN:SI:UM:
Type (COBISS): Master's thesis/paper
Thesis comment: Univ. v Mariboru, Fak. za kemijo in kemijsko tehnologijo
Pages: XI, 53 str.
ID: 9129414