Chromophoric Dissolved Organic Matter (CDOM): chemical structure and
PARAFAC analysis
Abstract
The structure(s), distribution and dynamics of CDOM have been
investigated over the last several decades largely through optical
spectroscopy (including both absorption and fluorescence) due to the
fairly inexpensive instrumentation and the easy-to-gather data (over
thousands published papers from 1990-2016). Yet, the chemical
structure(s) of the light absorbing and emitting species or constituents
within CDOM has only recently being proposed and tested through chemical
manipulation of selected functional groups (such as carbonyl and
carboxylic/phenolic containing molecules) naturally occurring within the
organic matter pool. Similarly, fitting models (among which the PArallel
FACtor analysis, PARAFAC) have been developed to better understand the
nature of a subset of DOM, the CDOM fluorescent matter (FDOM).
Fluorescence spectroscopy coupled with chemical tests and PARAFAC
analyses could potentially provide valuable insights on CDOM sources and
chemical nature of the FDOM pool. However, despite that applications
(and publications) of PARAFAC model to FDOM have grown exponentially
since its first application/publication (2003), a large fraction of such
publications has misinterpreted the chemical meaning of the delivered
PARAFAC ‘components’ leading to more confusion than clarification on the
nature, distribution and dynamics of the FDOM pool. In this context, we
employed chemical manipulation of selected functional groups to gain
further insights on the chemical structure of the FDOM and we tested to
what extent the PARAFAC ‘components’ represent true fluorophores through
a controlled chemical approach with the ultimate goal to provide
insights on the chemical nature of such ‘components’ (as well as on the
chemical nature of the FDOM) along with the advantages and limitations
of the PARAFAC application.