Spectroscopy of Aqueous Extracts of Forest Litter. I: Suitability of Methods

Abstract

Structural characteristics of dissolved organic matter (DOM) have not been closely examined until recent analytical techniques became available. We examined the applicability of ultraviolet‐visible (UV‐VIS), Fourier‐transform infrared (FTIR), and electron spin resonance (ESR) spectroscopies using aqueous extracts of pine and broadleaf understory leaf litter. The ratio of UV‐VIS absorbances at 465 nm and 665 nm (E4/E6) were 7.8 to 8.5 for extracts of pine and 6.3 to 7.7 for the understory between pH 3.0 and 6.0. Using the standard method for humic substances (in 0.05 M NaHCO3 solution, pH 8.0), E4/E6 measurement produced varying results, and is not recommended for DOM. Well‐resolved FTIR spectra had features similar to those of humic substances; peak‐height ratios were used for semiquantitative analysis of DOM functional groups. Two FTIR sample‐preparation procedures were also compared: dried extracts on AgCl disks, and freeze‐dried DOM in KBr pressed pellets. The first allowed better analysis of COOH functional group deprotonation; the second preparation procedure produced spectra with identical absorbance ranges as those of AgCl disks, with similar peak‐height ratio trends as a function of pH, except for those associated with COOH/COO−. Contact between DOM and the salt in pressed pellets may have aided deprotonation of COOH, even at low pH. Interference from water occurred with KBr pressed pellets. Free radicals identified by ESR increased with pH, and shifts from 2.0036 to 2.0050 in ESR g values indicated that oxidation also increased with pH. We conclude that these spectroscopic techniques, modified from those developed for analysis of humic substances, are complementary and together provide useful information about the structure of the DOM of forest litter.

Humic substances change during the co-composting process of municipal solid wastes and sewage sludge

“…The E 4 /E 6 ratio is used to characterize CHA and CFA. The E 4 /E 6 ratio value was indicative of the molecular size or chemical complexity degree of both CHA and CFA (Gressel et al 1995). E 4 /E 6 ratio explains the heterogeneity of the CHA studied because it is related to the degree of condensation of the aromatic carbon.…”

Membrane Pretreatment: A Method for Reducing Fouling by Natural Organic Matter

“…This system permitted monitoring of changes in the feed solution throughout the filtration process as the permeate was recycled to the feed tank. In addition, the configuration of the system ensured that all experimental conditions used for water sampling and flux determination were done at the same operating pressure (150 kPa), temperature (20 • C), and flow rate of 80 L/h.…”

“…Effects of membrane pretreatment on the fouling of capillary UF membranes were determined by measuring changes in the pure-water flux (PWF) and product flux (PF). The quality of the resultant permeate solutions after pretreatment was determined by ultraviolet-visible light spectroscopy (UV-vis) analyses [18][19][20]. Data from this study provided important information for the design of future UF plants for the treatment of NBW.…”

Contribution of humic substances from different composts to the synthesis of humin in a tropical soil

“…The quantitative level of this functional group was found to be on average 251 % higher than of the other composts (Table 3). The mineral enrichment of AS and SM composts favored mineralization of the precursors of the alkyl groups (Figure 1), as demonstrated by the reduction of the relative abundance compared to SC (Baldock & Preston, 1995;Gressel et al, 1996;Dai et al, 2001). In the latter, preferential decomposition of other fractions, such as carbohydrates, and preservation of the alkyl groups has probably occurred, reflected in the soil humin contents.…”