Multivariate Statistical Approaches for the Characterization of Dissolved Organic Matter Analyzed by Ultrahigh Resolution Mass Spectrometry

Abstract

We apply multivariate statistics to explore the large data sets encountered from Fourier transform ion cyclotron resonance mass spectra of dissolved organic matter (DOM). Molecular formula assignments for the individual constituents of DOM are examined by hierarchal cluster analysis (HCA) and principal component analysis (PCA), to measure the relationships between numerous DOM samples. We compare two approaches: (1) using averages of elemental ratios and double bond equivalents calculated from the formulas, and (2) employing individual formulas and either their presence/absence or relative magnitude in each sample. With approach 2, PCA deciphers which of the thousands of formulas are significant to particular samples, and then a van Krevelen diagram highlights what types of compounds are molecular signatures to the samples. Our dual approach, especially approach 2, allows for complex data sets to be more easily interpreted, aiding in the characterization of DOM from various sources. By applying this methodology, clear trends can be delineated, trends that are not apparent from currently employed methods. Terrestrial DOM contains various lignin-derived compounds, tannins, and condensed aromatics. Marine DOM contains aliphatic compounds with heteroatom functionalities, as well as lignin-like molecules.

Chemodiversity of dissolved organic matter in lakes driven by climate and hydrology

“…Using normalized peak intensities as opposed to presence/absence-based methods broadens the range of statistical tools available to study and interpret DOM patterns. In accordance with a previous study 44 , we find that utilizing normalized peak intensities reveals more detailed patterns and drivers of DOM quality than were apparent from only using presence/absence information, in both multivariate analyses ( Fig. 2 and Supplementary Fig.…”

Characterization of terrestrial dissolved organic matter fractionated by pH and polarity and their biological effects on plant growth

“…The C18 filtrate contains more heteroatoms than the C18 retentate (which is consistent with previous studies [23,30,36], as these polar species are not adsorbed to the C18 resin, especially the sulfur species (which are typically also associated with high oxygenation, such as sulfates, and are very polar). Also in Table 3 are the number-averaged and magnitude-weighted calculations.…”

“…All of the acquired FTICR mass spectra were similar to DOM samples analyzed previously [14,23,[33][34][35][36]38], with most peaks existing at 300-600 m/z. The majority of peaks appear at odd m/z values, and, based upon the nitrogen rule, indicate a predominance of zero or an even number of nitrogens in the molecules.…”

“…If a formula was not detected in that sample, a 0 was given in the matrix. Data were normalized for each sample so that the summed total magnitude equaled 1 for all samples, and PCA was conducted according to a previously published method [36].…”

Molecular transformation and degradation of refractory dissolved organic matter in the Atlantic and Southern Ocean

“…Currently, much effort is undertaken to overcome the analytical restrictions of this technique (Kido Soule et al, 2010;Sleighter et al, 2010Sleighter et al, , 2012Tfaily et al, 2011) and to refine the data evaluation algorithms (Kujawinski and Behn, 2006;Koch et al, 2007;Flerus et al, 2011;Tziotis et al, 2011). A particular drawback is that usually only small sample sets were analyzed, which hinders statistically robust generalizations to environmental applications.…”