Organic nitrogen in sediments of the Peru upwelling region

Nitrogen in fossil fuels is present in pyrrolic- and pyridinic-functional groups. In contrast, organic nitrogen in living organisms is overwhelmingly found in amino acids in proteins and peptides. Petroleum is the result of the maturation of the organic remains of organisms, so what causes the change in nitrogen functionality between organisms and oil, and when does it occur? Using X-ray photoelectron spectroscopy (XPS) supported by elemental analysis, biochemical analysis, and pyrolysis-gas chromatography with atomic emission detection (py43C-AED) for nitrogen, surface sediments from the Peru upwelling region were shown to contain at least four different organic nitrogen-containing functional groups: amino, pyrrole, pyridine and (tentatively) quaternary nitrogen. The percent in amino groups is at most 40-45%, and possibly as little as 10-15%. Heterocyclic nitrogen (pyrroles and pyridines) makes up a greater proportion of the total than amino N, with pyrroles more abundant than pyridines. With increasing burial depth, the percentage of total N present as amino nitrogen declines to low levels, whilst the proportion present as (tentatively) quaternary nitrogen increases. Pyrroles are always more abundant than pyridines. These semi-quantitative data suggest that the pyrrolic and pyridinic structures, found in petroleums and coals, are present at a very shallow burial depths in the Peru upwelling sediments.