engleski

LC and HPLC methods as a preparation steo of bomarker samples

The geochemical biomarkers are molecular fossils derived from once living organisms, through a number of complex chemical reaction during diagenesis. From the chemical point of view they are complex organic compounds composed of carbon, hydrogen and other elements and can be found in the source rocks, sediments and crude oil. Biomarkers can posses a simple structure similar to that of linear chain hydrocarbons or a very complex structure (steroids). Biomarkers can be determined by "screening" technique (GC), but for quantitive determination a hyphenated chromatographic technique like GC/MS, GC/MS/MS were indispensable. There are a different approaches in the preparation of samples for measurements depending on the sources. Source rocks need complex procedure in order to obtain sample for measurements (maltene) . The process of preparation is more easier if sample is crude oil. If a maltene fraction of each samples is reached in biomarker content direct determination by GC/MS, is possible. But this is a very rare case and usualy the sample needs some preconcentration. If the goal is saturated based biomarkers all other groups have to be removed. If the goal is steroids, an aromatic fraction has to be isolated and fractionated. For this step a column liquid chromatography and high performance liquid chromatography (HPLC) were used. Column liquid chromatography was performed on Pasteur pipette filled with aluminium oxide or silicum oxide. Dichlormethane, methanol and pentane were used as a mobile phase. For quantitive determination of present hydrocarbon group (saturates, mono, di and poly aromatics) a NP HPLC with back flash valve were used. If a maltene samples are reached with particular hydrocarbon group, a collected fraction by repeatied analytical NP HPLC are enough for further GC and GC/MS analysis. To overcome time comsuming, tedius procedure a semipreparative HPLC could be used. Determined content of biomarkers and their ration obtaned by GC/MS were discused and compared depending on applied preparation technique.

preparative NP HPLC ; biomarkers analyis

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