Vario el 3 elemental analyzer

Sediment samples were analyzed for stable isotopes of nitrogen, as well as for %C and %N, at the Ján Veizer Stable Isotope Laboratory (University of Ottawa, ON). The molar ratio of C:N can be used as an approximate measure to assess whether sedimentary organic matter is largely of aquatic (C:N < 10) or terrestrial (C:N > 20) origin (Meyers & Ishiwatari, 1993 ). For elemental %C and %N analysis, sediment samples and standards were analyzed using a Vario EL III Elemental Analyzer (Elementar, Germany). Sediment amounts needed for the δ¹⁵N isotopic analyses were determined based on the results of the elemental analysis and weighed accordingly into tin capsules with two parts tungsten trioxide (WO₃). The isotopic composition of nitrogen was determined by the analysis of N₂, produced by combustion on a VarioEL III Elemental Analyzer (Elementar, Germany) followed by “trap and purge” separation and online analysis by continuous‐flow with a DeltaPlus XP Plus Advantage Isotope Ratio Mass Spectrometer coupled with a ConFlo II (Thermo, Germany). Our δ¹⁵N data were reported using delta (δ) notation in parts per thousand (‰) enrichments or depletions relative to common standards (AIR for δ¹⁵N). Isotope data were normalized using previously calibrated internal standards, and analytical precision was ±0.2%. δ¹⁵N data was not obtained for A085 and C:N data for D004, D016, and A085.

An Elementar Vario EL III Elemental Analyzer was used to determine the carbon/nitrogen ratio of the crude chitin extracted. 5 mg of the crude chitin was added to a preformed tin foil boat, after which the boat was folded into a pellet and loaded into a sample carousel. Once dropped into the instrument, the chitin sample undergoes catalytic tube combustion in an oxygenated, high temperature CO₂ atmosphere. Helium carries carbon and nitrogen through specific adsorption columns where the components are separated and their concentrations determined by a thermal conductivity detector. The carbon/nitrogen ratio was measured to correlate with the decomposition rates of organic material present in the prawn waste by fermentation (Haynes 2014 ).

FT-IR spectra of chitosan and GCS were recorded using the KBr disk method (Bruker Vector 33, Bruker Corporation, Karlsruhe, Germany). ¹H NMR spectra were recorded on a Bruker Avance 400 NMR Spectrophotometer (Bruker Corporation, Karlsruhe, Germany) using 1 wt % CD₃COOD in D₂O as solvent to characterize the structures of chitosan and GCS. All samples were further vacuum dried at 60 °C for 2 days prior to the measurements. The degree of substitution (DS) of GCS was calculated by the followed equations where C/N was determined by elemental analysis (Vario EL III Elemental Analyzer, Elementar Analysensysteme GmbH, Langenselbold, Germany), m is the polymerization degree of PHGC, and 95% is the deacetylation degree of chitosan.
$C/N=\frac{6\times 12\times 95\%+7\times 12\times 5\%+7\times 12\times m\times DS}{1\times 14+3\times 14\times m\times DS}=\frac{72.6+84\times m\times DS}{14+42\times m\times DS}$
$DS=\frac{14C/N-72.6}{(84-42C/N)\times m}$