Organically bound sulfur in refractory organic substances

Area of Science:

• Environmental Chemistry
• Organic Geochemistry
• Biogeochemistry

Background:

• Refractory organic substances (ROS) are complex organic materials resistant to degradation.
• Understanding the sulfur speciation in ROS is crucial for environmental and geochemical studies.
• The origin and formation conditions significantly influence the composition of ROS.

Purpose of the Study:

• To characterize sulfur compounds in refractory organic substances (ROS) from various sources.
• To determine the abundance and types of sulfur-containing amino acids in ROS.
• To compare different analytical methods for sulfur speciation in ROS.

Main Methods:

• Elemental analysis for total organic sulfur determination.
• Chromatographic analysis of sulfur-containing amino acids (methionine, cystine) after acid hydrolysis.
• Proteolytic digestion using enzymes to release amino acids.
• Comparison with potentiometric titration, differential reduction, and spectroscopic methods.

Main Results:

• Total sulfur content in ROS is highly dependent on sample origin and environmental factors.
• Carbon-to-sulfur (C/S) atomic ratios decrease with humification in natural samples due to carbon loss.
• Cystine was a significant sulfur-containing amino acid released, while methionine was often below detection limits.
• Acid hydrolysis released more amino acids than enzymatic digestion, suggesting non-proteinaceous sulfur forms.

Conclusions:

• Sulfur speciation in ROS is complex and influenced by origin and environmental conditions.
• Cystine plays a critical role in the sulfur composition of ROS.
• Analytical methods impact the assessment of bioavailable sulfur compounds in ROS.