Modern analytical studies of humic substances

Analytical chemistry has played a pivotal role in soil science, providing an avenue for advances in knowledge and understanding of the transformation, reactivity, and occurrence of chemical compounds in soil. Organic matter, perhaps the least known area of soil, has generally suffered from a lack of suitable techniques for its characterization, but that is changing rapidly as new analytical methods, used primarily in the biochemistry field, are being applied. This review is intended to highlight some of the techniques that are used routinely in advanced studies of soil organic matter, primarily the complex humic substances. Our focus is on modern methods of pyrolysis gas chromatography-mass spectrometry, thermochemolysis with tetramethylammonium hydroxide coupled to gas chromatography-mass spectrometry, modern soft-ionization mass spectrometry, and solid-state nuclear magnetic resonance spectroscopy. Although these methods have been used in past studies, there are now new developments in need of review.