Methods for Characterization & Analysis of NOM

This project was aimed at improving our quantittative and qualitative understanding of NOM used for drinking water in the US. Most of the work was in data collection and analysis from: (1) mail and literature surveys, (2) statistical analysis of existing databases and (3) laboratory analysis of samples collected from participating utilities. Mail surveys were sent to 553 of the largest utilities in the US using surface water (Chapter 3), requesting information on organic carbon levels, source types, land use characteristics and utility interest in these issues. New data were generated on DBP formation (Chapter 4) in a range of natural waters and extracted NOM fractions. These data were compared with similar data acquired from an extensive literature search (NA database). Chapter 5 opens with a fresh review of BOM assay techniques as they pertain to drinking water followed by a new set of data on NOM fractionation and characterization generated for this report. Two sets of long-term experiments aimed at quantifying the generation of DOM from leaf litter and its subsequent biodegradation were conducted (Chapter 6). Data presented in chapter 7 focused on lignin and its various substructures. Short-term and long-term temporal trends in a few watersheds were used to infer some key fate and transport mechanisms (Chapter 8). Finally the large body of data on TOC in US waters was mined for the purpose of capturing information on the link between TOC levels and watershed characteristics, as well as to look for long term changes (Chapter 9).

The following NOM isolation methods were compared: RO, NF, adsorption to XAD-8, XAD-4, oliving and iron-oxide coated sand. NOM from two water sources was fractionated based on hydrophobicity and acdity, andf the various fractions were compared using: 13C-NMR, Pyr-GC/MS, FTIR, elemental analysis, total dissolved carbohydrates, amino acids, UV spec, fluorescence and reactivity.

Bulk NOM and isolated fractions were characterized by DOC, UV abs, fluorescence, chlorine demand and DBP precursor tests. The DBP tests included 96-hr formation potential tests, and 24 hr simulated distribution system tests. THMs, HAAs adn HANs were measured. Source waters used inlcude those from MWDSC (CRW & SPW), Phoenix, Ohio River, Newport News, BHC and Biscayne Aquifer

The sorptive behavior of resins XAD2, -4, and -7 for dissolved organic carbon (DOC) derived from marine phytoplankton was compared. The resins were arranged in varying sequences, which proved to be critical for determining the efficiency of DOC isolation. The sequence XAD7/2/4 allowed the isolation of a very high percentage of DOC (65%) from the seawater matrix. A mixed bed of the same resins showed a significantly lower recovery (39%). Varying amounts of the material adsorbed by the individual resins could not be recovered by NaOH/methanol elution. The percentage of DOC firmly retained by each resin was 32, 21, and 2% in XAD2, XAD4, and XAD7, respectively

The XAD8 and XAD4 resins, used in series, show different behaviours in relation to the retention of dissolved organic matter (DOM) from estuarine water samples according to different salinities. For the XAD8 resin, the removal of DOM measured in terms of light absorbance at 250 nm varies from 69.4% +/- 0.5 to 51.4% +/- 3.5 and for the XAD4 resin it varies from 20.0% +/- 1.0 to 25.2% +/- 3.0 for salinities ranging from 0.6 to 33.4. The isolation, with XAD8, of DOM from samples increasing in salinity, measured in terms of emission fluorescence intensity at selected wavelengths (410, 440 and 460 nm) for an excitation of 340 nm, decreases. In the same experimental conditions, the increase of fluorescent organic matter (FOM) removed by the addition of XAD4 resin is always greater than 20%. However, addition of NaCl to the sample with the lowest salinity, shows that the retention in both resins is related more to the nature of DOM than to the ionic strength of the sample.

The XAD-2010 and XAD-16 polystyrene based resins have for the first time been used for the isolation of humic substances (HS) from seawater in this study. The adsorption efficiencies and recoveries of HS were compared using batch and column isolation procedures with different XAD resins (XAD-2, -4, -16, -2010 and XAD-4+XAD-2, XAD-2010+ XAD-16, XAD-16+XAD-2010). The recoveries of adsorbed HS were evaluated by the comparison of the size-exclusion chromatogram (SEC) peak areas of the seawater sample and of the NaOH effluents from different XAD columns. The batch recoveries of adsorbed HS varied between 35.2+/-2.4% (XAD-4) and 72.5+/-5.2% (XAD-2010). The XAD-16 resin had the best adsorption properties (column procedure, recovery 89.5+/-0.5%) and XAD-2010 the best elution properties for seawater HS. The batch isolation procedure for seawater HS has been worked out. (C) 1999 Elsevier Science B.V. All rights reserved.

Aquatic humic solutes were separated in parallel by the non-ionic macroporous DAX-8 and XAD-8 resins from four different fresh water sources. On average, the sorptive power of the DAX-8 resin does not differ systematically from that of the XAD-8 resin. The DAX-8 resin seems to have more precise column characteristics compared with the XAD-8 resin. There was no significant difference between the major elemental compositions of the parallel humic-solute bulks obtained by these two resins. According to the C-13 NMR spectroscopy the content and quality of aliphatic carbons, especially those representing terminal methyl groups or methylene carbons, were the most systematic and powerful discriminating factors between the humic extracts obtained by these two resins. Generally speaking the DAX-8 and XAD-8 resins seem to isolate humic-solute bulks almost equally, although the content of aliphatics is slightly greater for the former, producing mixtures with similar structural compositions for general purposes. The structural composition and quantity of the humic-solute mixture isolable with a weakly basic DEAE-cellulose anion exchange resin differs partially from any humic fraction obtained by non-ionic sorbing solids. The environmental impact was also visible on the quality of the structural fine-chemistry of the different humic isolates obtained both by the DAX-8 and XAD-8 resins

The polarity rapid assessment method (PRAM) characterizes the polarity of aqueous natural organic matter (NOM) by quantifying the amount of material adsorbed onto different solid-phase extraction (SPE) sorbents. The analysis is performed under ambient conditions resulting in the elimination of pretreatment steps that may alter the chemical characteristics of the NOM, allowing an accurate representation of its polarity as it exists in the environment. Additionally, analysis only requires 200 mL of sample and can be performed in 2 h. In this paper, the underlying theory of the method is presented, followed by its optimization, with emphasis on the development of conditions for the analysis of NOM in natural waters. A series of organic probe compounds showed that the most important physicochemical property describing the interaction between the NOM and the SPE sorbents was the hydrophobic surface area, allowing for the estimation of the hydrophobic character under ambient conditions. Evaluation of the effects of chemical concentration, pH, and ionic strength show that (1) concentration did not have an effect on PRAM characterization as long as the pH and ionic strength remained constant; (2) changes in pH and ionic strength resulted in considerable changes in PRAM characterization, as a result of the changes in configuration of the NOM; and (3) PRAM characterization of NOM can be completed in the concentration range of < 10 mg C/L, although this range could be expanded by evaluating the effect of concentration on a site-specific basis. Results indicate that measurement of both ultraviolet absorption and dissolved organic carbon show complementary results as they measure different aspects of NOM.

A new technique has been developed to quickly monitor the changes in polarity of aqueous natural organic matter (NOM) using solid-phase extraction (SPE) cartridges. This paper introduces the NOM polarity rapid assessment method (PRAM). The PRAM technique characterizes changes in NOM polarity by monitoring the breakthrough curves from different SPE cartridges at UV254. The SPE cartridges used in this study include a wide range of polarity from non-polar C-18 materials to anion exchangers. Each individual cartridge run takes 10 minutes and requires about 15 ml of sample. The collected water sample matrix is not changed, i.e. all PRAM analyses were done under ambient conditions on the original sample. Polarity evaluation is completed without the sample being exposed to changes in sample conditions, such as pH, solvent extraction, sequential evaporations or freeze-drying. This technique was able to monitor the weekly changes in NOM polarity entering a water treatment plant and compares the effects of different water treatment processes on this material.

High-performance liquid chromatography-size exclusion chromatography (HPLC-SEC) coupled with a multiple wavelength absorbance detector (200-445 nm) was used in this study to investigate the apparent molecular weight (AMW) distributions of dissolved organic matter (DOM). Standard DOM, namely humic acid, fulvic acid and hydrophilic acid, from the Suwannee River were tested to ascertain the performance and sensitivity of the method. In addition to four compounds groups: humic substances (Peak 1, AMW 16 kD), fulvic acids (Peak 2, AMW 11 kD), low AMW acids (Peak 3, AMW 5 kD), and low AMW neutral and amphiphilic molecules, proteins and their amino acid building blocks (Peak 4, AMW 3 kD), an new group that appears to include low AMW, 6-10 kD, humic substances was found based on investigating the spectra at various elution times. The spectroscopic parameter S->365 (slope at wavelengths >365 nm) was determined to be a good predictor of the AMW of the DOM. The detector wavelength played an important role in evaluating the AMW distribution. For some fractions, such as the humic and low AMW non-aromatic substances, the error in measurement was +/- 30% as determined by two-dimensional chromatograms detected at an artificially selected wavelength. HPLC-SEC with multiple wavelength absorbance detection was found to be a useful technique for DOM characterization. It characterized the AMW distributions of DOM more accurately and provided additional, potentially important information concerning the properties of DOM with varying AMWs.

Size exclusion chromatography (SEC) in combination with continuous organic carbon detection (OCD) is a powerful analytical technique that enables characterization of dissolved organic water constituents. Low molecular weight organic water constituents are ubiquitous but their behaviour in SEC analyses is not yet fully clarified. Therefore, we analysed a number of low molecular weight organic model compounds with various structural and functional characteristics by size exclusion chromatography combined with online OCD and ultraviolet light absorption measurement (UVD). The detection times of some low molecular weight organic compounds were much lower than expected. Elution behaviour of low molecular weight compounds (below 300 g/mol) was determined by functional groups rather than by molecular weight. Retention times of low molecular weight compounds varied between 51.9 min, close to that of humic substances, and 235 min of benzaldehyde, the double value of a standard chromatogram runtime of 120 min. Comparisons of both detectors' signals reveal that elution times and detection times are not identical. The elution sequence of various model compounds provided here facilitates identification of peaks in the low molecular weight range of SEC chromatograms.

A new type of high-performance liquid chromatography (HPLC) size exclusion chromatography (SEC) system with ultraviolet (UV) absorbance detection and non-dispersive infrared (NDIR) detection of total organic carbon is described. The introduction of an online degassing tube and a low-volume HPLC column helped to reduce the analytical time and increase the sensitivity of the SEC system. This study is the first in which linear calibration curves (R(2) > 0.99) were obtained for both UV absorbance and NDIR data for polystyrene sulfonate standards, which are the most suitable standards for molecular size analysis of aquatic humic substances as well as dissolved organic matter (DOM). Using the calibration curves, the molecular size distribution of DOM in water collected from Lake Kasumigaura and in pore water from lake sediments was estimated. Most of the DOM had a molecular weight less than 4000 Daltons (Da), and the amount of low-molecular-weight DOM (similar to 2000 Da) with low UV absorbance increased with depth in the sediment pore water. This result shows the importance of combining quantitative analysis by NDIR detection with qualitative analysis by UV detection to determine the chemical and physical properties of DOM. The possible sources and reactivity of DOM in Lake Kasumigaura and its sediment pore water are also discussed.

Permanent need to understand nature, structure and properties of humic substances influences also separation methods that are in a wide scope used for fractionation, characterization and analysis of humic substances (HS). At the first glance techniques based on size-exclusion phenomena are the most useful and utilized for relating elution data to the molecular mass distribution of HS, however, with some limitations and exceptions, respectively, in the structural investigation of HS. The second most abundant separation mechanism is reversed-phase based on weak hydrophobic interactions beneficially combined with the step gradients inducing distinct features in rather featureless analytical signal of HS. Relatively great effort is invested to the developments of immobilized-metal affinity chromatography mimicking chelate-forming properties of HS as ligands in the environment. Surprisingly, relatively less attention is given to the ion-ion interactions based ion-exchange chromatography of HS. Chromatographic separation methods play also an important role in the examination of interactions of HS with pesticides. They allow us to determine binding constants and the other data necessary to predict the mobility of chemical pollutants in the environment. HS is frequently adversely acting in analytical procedures as interfering substance, so more detailed information is desired on manifestation of its numerous properties in analytical procedures. The article topic is covered by the review emphasizing advances in the field done in the period of last 10 years from 2000 till 2010.

Size-exclusion chromatography in combination with organic carbon detection (SEC-OCD) is an established method to separate the pool of NOM into major fractions of different sizes and chemical functions and to quantify these on the basis of organic carbon. One specific approach, also known as LC-OCD-OND, is based on the Grantzel thin-film UV-reactor. This approach is described with recent improvements in fraction assignation (humic substances, biopolymers, building blocks, low molecular weight organic acids and neutrals, hydrophobic organic carbon), the coupling of a novel organic nitrogen detector (OND), and an improved diagram for the characterisation of aquatic humic substances (HS-diagram). The diagram replaces the operational distinction between humic and fulvic acids by a continuum ranging from aquagenic fulvic acids to pedogenic humic acids.

Natural organic matter (NOM) is of concern in drinking water because it causes adverse aesthetic qualities such as taste, odour, and colour; impedes the performance of treatment processes; and decreases the effectiveness of oxidants and disinfectants while contributing to undesirable disinfection by-products. The effective removal of NOM during drinking water treatment requires a good understanding of its character. Because of its heterogeneity, NOM characterization necessitates the use of multiple analytical techniques. In this study, NOM in water samples from two drinking water treatment trains was characterized using liquid chromatography with organic carbon detection (LC-OCD), and fluorescence excitation-emission matrices (F-EEMs) with parallel factor analysis (PARAFAC). These characterization methods indicate that the raw and treated waters are dominated by humic substances. The results show that whereas the coagulation process for both plants may be optimized for the removal of bulk DOC, it is not likewise optimized for the removal of specific NOM fractions. A five component PARAFAC model was developed for the F-EEMs, three of which are humic-like, while two are protein-like. These PARAFAC components and the LC-OCD fractions represented effective tools for the performance evaluation of the two water treatment plants in terms of the removal of NOM fractions.

The evaluation of the molecular size distribution of natural organic matter (NOM) in aquatic environments via size exclusion chromatography (SEC) is important for the understanding of environmental processes such as nutrient cycling and pollutant transport as well as of technical water treatment processes. The use of organic carbon (OC) detectors has become popular in recent studies due to improved availability and quantification possibilities, which supposedly are superior to those of ultraviolet (UV) detectors. A set of 12 NOM samples was used to demonstrate the limitations of online OC detection (OCD) when analyzing complex aquatic organic matter. A novel evaluation approach for SEC data is introduced by combining the information from UV absorbance (UVA) and OCD chromatograms as well as offline total OC (t-OC) and dissolved OC-specific UVA (SUVA) measurements. It could be shown that about 70% of certain OC components were not detected with the OCD system used in this study. For the investigated samples, these types of carbon accounted for up to 72% of the t-OC, i.e. for such NOM samples quantification by OCD is not possible or at least highly questionable. The addition of an oxidant improved the overall oxidation efficiency only slightly. Most likely NOM that predominantly consists of polysaccharides and features a nominal molecular weight of 150 kg/mol or more was responsible for low OCD yields. For future applications, a further improvement of the OCD system would be worthwhile so that quantitative analytical data on the molecular size distribution of NOM and its structural characteristics such as the SUVA distribution can be obtained.

A novel organic carbon detector for size-exclusion chromatography (SEC) is described. The instrument uses the conventional UV-persulfate oxidation method to convert organic carbon to CO2, which is then detected using a mass spectrometer. This system, using the mass spectrometer, had lower limits of detection (LOD) and limits of quantification (LOQ) than a previously described system using a Fourier transform infrared (FTIR) spectroscopy 'lightpipe' detector (i.e. when quantification was based on calibration using phthalate standards). When used to analyse natural organic matter (NOM) in water, it also had a superior signal-to-noise ratio to the previously described system. The use of a mass spectrometer to detect organic carbon (as CO2) enables the possibility of further characterisation of NOM by measuring the stable carbon isotope ratios of the various molecular size fractions of organic carbon, as obtained by SEC.

A novel organic carbon detector (OCD) for size exclusion chromatography (SEC), and its application to the characterisation of aquatic natural organic matter (NOM) in natural and treated potable water samples, is described. The instrument uses a conventional UV-persulfate oxidation technique to convert organic carbon to CO2. The novelty of the technique is detection of the evolved CO2 using a sensitive Fourier transform infrared (FTIR) spectroscopy 'lightpipe' detector originally designed for detection of analytes after gas chromatographic separation. With the exception of the lightpipe, the OCD system was constructed using simple, inexpensive, readily available components. The system was designed to minimise deadvolume, allowing for use of smaller sample sizes and smaller columns, substantially shortening analysis time, while maintaining chromatographic integrity through the OCD system. Downscaling resulted in some loss of separation but it was shown that this was caused by the lower separation efficiency of the smaller capacity column, rather than from sample dispersion within the OCD system

Trihalomethanes (THMs) are produced during chlorination of water. Three predictive models for estimating/calculating THM formation exist, but because eventual THM concentrations cannot be calculated precisely from conventional analyses, methods to determine the potential for forming THMS are useful in evaluating water treatment processes or water sources or for predicting THM concentrations in a distribution system. Three methods are given: trihalomethane formation potential (THMFP) (5710B); simulated distribution system trihalomethanes (SDS-THM) (5710C); and, formation of other disinfection byproducts (DBPs) (5710D). The 2010 version includes new references to the QC practices considered to be an integral part of each method.