Vario el 3 chnos

Chemicals used in the experiments were obtained from Merck (Darmstadt, Germany) except for spin-trap DEPMPO which was purchased from Enzo Life Sciences (Farmingdale, NY, USA). All of the chemicals were of the analytical grade. The IR vibrational spectra were recorded on the Perkin-Elmer Spectrum (Bruker, Germany. Model: 197). One FT-IR spectrometer using the KBr pellet technique. The NMR spectra were obtained on the Varian Gemini spectrometer (Varian, Palo Alto, CA, 200 MHz for ¹H and 50 MHz for ¹³C) in DMSO-d6. The elemental microanalysis (C, H, N) was performed on the Elemental analysis system VARIO EL III CHNOS, model—Elementar Analysensysteme (GmbH, VarioEL, Germany), 2003 in the Centre for Instrumental Analysis, at the Faculty of Chemistry, University of Belgrade.

Total nitrogen (TN) and total carbon (TC) were measured, using a Vario EL III CHNOS elemental analyzer (Elementar Analysensysteme, Hanau, Germany). Each sample tin cup was loaded with 8–9 mg of freeze-dried, powdered sediment plus a spatula tip of tungsten oxide (WO₃) to enhance the combustion, and then combusted at 1150°C. Detection limit is below 0.1%. TC results were used to calibrate volumes of sample required for total organic carbon (TOC) measurements. For TOC analysis, between 30 and 70 mg of sediment powder were loaded into a crucible and burnt at 580°C (sensitive carbon T° for non-calcareous samples), 850 and 1150°C (intensive carbon T° for calcareous samples) using a Vario MAX cube elemental macro analyzer (Elementar Analysensysteme), equipped with the soliTIC option for the determination of the total organically bound and inorganic carbon in the sample. Pretreatment of samples with HCl (5%), as is normally done for standard elemental analyzers (Byers et al., 1978 (link)) is not needed with this device. TOC and TN were recalculated to the content of the whole sample to present results in dry mass %. TOC and TN values were then corrected by their respective atomic weights (i.e., 14/12) and used to calculate molar C_org/N ratios.