Nominal Molecular Weight Fractions Research Articles

Influence of Different Nominal Molecular Weight Fractions of Humic Acids on Phenol Oxidation by Permanganate

The effects of humic acid (HA) and its different nominal molecular weight (NMW) fractions on the phenol oxidation by permanganate were studied. Phenol oxidation by permanganate was enhanced by the presence of HA at pH 4-8, while slightly inhibited at pH 9-10. The effects of HA on phenol oxidation by permanganate were dependent on HA concentration and permanganate/phenol molar ratios. The high NMW fractions of HA enhanced phenol oxidation by permanganate at pH 7 more significantly than the low fractions of HA. The apparent second-order rate constants of phenol oxidation by permanganate in the presence of HA correlated well with their specific ultraviolet absorption (SUVA) at 254 nm and specific violet absorption (SVA) at 465 or 665 nm. High positive correlation coefficients (R(2) > 0.72) implied that pi-electrons of HA strongly influenced the reactivity of phenol towards permanganate oxidation which agreed well with the information provided by fluorescence spectroscopy. The FTIR analysis indicated that the HA fractions rich in aliphatic character, polysaccharide-like substances, and the amount of carboxylate groups had less effect on phenol oxidation by permanganate. The negative correlation between the rate constants of phenol oxidation by permanganate and O/C ratios suggested that the oxidation of phenol increased with a decrease in the content of oxygen-containing functional groups.

Spectroscopic study of humic acids fractionated by means of tangential ultrafiltration

Different chemical and spectroscopic techniques—diffuse reflectance infrared Fourier transform (DRIFT), surface-enhanced Raman spectroscopy (SERS), and 1H, 13C nuclear magnetic resonance (NMR) have been applied to investigate a peat humic acid (HA) separated by tangential ultrafiltration into different nominal molecular weight (NMW) fractions.Each fraction analyzed showed a characteristic DRIFT and NMR pattern. High nominal molecular weight fractions were mainly characterized by long chains of methyl and methylene groups and poorly substituted aromatic rings, while in low nominal molecular weight fractions (L-NMW), phenolic and oxygen-containing groups were predominant. A comparative study on fractions before and after treatment with 0.5M HCl was carried out. Purified fractions showed either an increase in the carboxylate and phenolic OH groups or an improvement in signal-to-noise ratio of their NMR spectra.The SERS study of NMW fractions allowed significative information on structure and conformation of these fractions. In particular, L-NMW fractions showed a great structural modification, when different alkaline extractants or treatment with HCl were used.Humic-like substances obtained by catechol and gallic acid polymerization on metal surface were investigated using SERS. The SERS spectra of these polymers were compared and discussed with those of NMW HA fractions.

Terrigenous dissolved organic matter along an estuarine gradient and its flux to the coastal ocean

The contribution of terrigenous organic matter (TOM) to high molecular weight dissolved and particulate organic matter (POM) was examined along the salinity gradient of the Delaware Estuary. Dissolved organic matter (DOM) was fractionated by ultrafiltration into 1–30 kDa (HDOM) and 30 kDa–0.2 μm (VHDOM) nominal molecular weight fractions. Thermochemolysis with tetramethylammonium hydroxide (TMAH) was used to release and quantify lipids and lignin phenols. Stable carbon isotopes, fatty acids and lignin content indicated shifts in sources with terrigenous material in the river and turbid region and a predominantly algal/planktonic signal in the lower estuary and coastal ocean. Thermochemolysis with TMAH released significant amounts of short chain fatty acids (C9–C13), not seen by traditional alkaline hydrolysis, which appear to be associated with the macromolecular matrix. Lignin phenol distributions in HDOM, VHDOM and particles followed predicted sources with higher concentrations in the river and turbid region of the estuary and lower concentrations in the coastal ocean. TOM comprised 12% of HDOM within the coastal ocean and up to 73% of HDOM within the turbid region of the estuary. In the coastal ocean, TOM from high molecular weight DOM comprised 4% of total DOC. The annual flux of TOM from the Delaware Estuary to the coastal ocean was estimated at 2.0×1010 g OC year−1 and suggests that temperate estuaries such as Delaware Bay can be significant sources of TOM on a regional scale.

Characterization of Natural Organic Matter Using High Performance Size Exclusion Chromatography

High performance size exclusion chromatography (HPSEC) was used to obtain the molecular weight distributions of natural organic matter (NOM) from two South Australian drinking water sources. The NOM was separated into five nominal molecular weight fractions ( 30K) using ultrafiltration membranes prior to HPSEC analysis. The use of HPSEC as a tool for NOM characterization was compared with an independent method, flow field−flow fractionation (FlFFF), which separates molecules via a different mechanism. Unlike HPSEC, which uses a porous gel with a controlled pore size distribution to separate molecules, FlFFF uses hydrodynamic and molecular diffusion principles to separate molecules on the basis of molecular size, in the absence of a porous gel. The comparison was made using the following parameters: weight-average molecular weight (Mw), number-average molecular weight (Mn), peak molecular weight (Mp), polydispersivity (Mw/Mn), and molecular weight range (80% confidence l...

Influence of characterised natural organic material on activated carbon adsorption: I. Characterisation of concentrated reservoir water

Natural organic material (NOM) from Myponga Reservoir in South Australia was concentrated and fractionated using ultrafiltration into nominal molecular weight fractions < 500, 500–3000, 3000–10,000, 10,000–30,000 and > 30,000. The fractions were characterised using flow field-flow fractionation, 13C NMR, colour determination and potentiometric titration. The ultrafiltration fractions displayed a gradual transformation from highly coloured, highly branched, high carbohydrate structures to compounds with a prevalence of long chain aliphatic carbon with much lower carbohydrate content and colour. There were no clear trends in the carboxyl content of the fractions, as determined by both NMR and titration. Analysis of the titration data showed evidence of three distinct types of carboxyl groups and the same types of groups were present in each fraction.

Characterization of Chlorolignins in Bleached Kraft Pulp Mill Effluents Using Elemental Analysis and Fingerprinting by CuO Oxidation And Hplc

Abstract Elemental analyses and chemical degradation techniques were applied to characterize lignin compounds in different stages of the chlorine bleaching process and in total mill effluent. Ultrafiltration was used for separation of chlorolignins into three nominal molecular weight fractions. Alkaline CuO oxidation products were analyzed by HPLC with diode array detection. Major compounds were identified by reference to authentic compounds. For comparison, native lignins (MWL), kraft lignins, and humic substances were studied as well. The oxygen, carbon and organic chlorine contents were closely similar in the various mill samples and their fractions. In all mill samples, vanillin and 6-chlorovanillin were the most abundant CuO oxidation products. There were no essential differences between the effluents before and after the activated sludge treatment. The results indicate the stability of chlorolignins during the bleaching and in particular during the purification. The fingerprint CuO/HPLC and elementa...

Relative copper binding capacities of dissolved organic compounds in a coastal-plain estuary

Naturally occurring organics in samples taken from the mesohaline portion of a Chesapeake Bay tributary were separated into four nominal molecular weight fractions and analyzed for their ability to bind copper by using an algal bioassay. The organics exhibited a relatively high capacity for copper, with the binding capacity directly proportional to dissolved organic carbon (DOC) concentrations. The relationship between binding capacity and DOC is similar in the Chesapeake Bay and in other estuaries and marine ecosystems. Such correlation is not found in freshwater ecosystems. The strong relationship between DOC concentrations and binding capacities in marine ecosystems may be due to the autochthonous origin of marine organics. 44 references, 3 figures, 2 tables.

CHANGES IN MOLECULAR WEIGHT DISTRIBUTION OF SOIL ORGANIC MATTER DURING SOIL DEVELOPMENT

SummaryTen different topsoils representing members of three soil chronosequences were pre‐treated with 0.1 M HC1 and extracted with neutral 0.1 M Na4P2O7 followed by 0.5 M NaOH. Extracts were purified and fractionated into five different nominal molecular weight fractions using gel filtration. With increasing soil development, the proportion of large molecules (&gt;200 000) in the organic matter decreased with an increase in the proportion of intermediate size molecules (200 000 – 10 000). This effect was more evident in the mild Na4P2O7 extracts than in the subsequent NaOH extracts, and in soils of the Manawatu chronosequence than in those of the other two chronosequences and are attributed to changes in the nature and humification of soil organic matter during soil development.