Nitrate determination using anion exchange membrane and mid-infrared spectroscopy

This study investigates the combined use of an anion exchange membrane and transmittance mid-infrared spectroscopy for determining nitrate concentration in aqueous solutions and soil pastes. The method is based on immersing a small piece (2 cm(2)) of anion exchange membrane into 5 mL of solution or soil paste for 30 minutes, after which the membrane is removed, rinsed, and wiped dry. The absorbance spectrum of the charged membrane is then used to determine the amount of nitrate sorbed on the membrane. At the levels tested, the presence of carbonate or phosphate does not affect the nitrate sorption or the spectrum of the charged membrane in the vicinity of the nitrate band. Sulfate affects the spectrum of the charged membrane but does not prevent nitrate determination. For soil pastes, nitrate sorption is remarkably independent of the soil composition and is not affected by the level of soil constituents such as organic matter, clay, and calcium carbonate. Partial least squares analysis of the membrane spectra shows that there exists a strong correlation between the nitrate charge and the absorbance in the 1000-1070 cm(-1) interval, which includes the v(1) nitrate band located around 1040 cm(-1). The prediction errors range from 0.8 to 2.1 mueq, which, under the specific experimental conditions, corresponds to approximately 2 to 6 ppm N-NO(3)(-) on a solution basis or 2 to 5 mg [N]/kg [dry soil] on a dry soil basis.     

Determination of organic and inorganic carbon in forest soil samples by mid-infrared spectroscopy and partial least squares regression

Analyses of organic and inorganic carbon are of great interest in the field of soil analyses. Soil samples from a national monitoring project were provided for this study, including more than 130 forest sites from Austria. We investigated the humus layers (if present undecomposed litter (L), of mixed samples of F- (intermediate decomposed organic matter) and H-(highly decomposed organic matter) (FH)) and upper mineral soil layers (0-5 and 5-10 cm) of the samples. Mid-infrared spectra were recorded and evaluated by their band areas; subsequently we calculated models with the partial least squares approach. This was done by correlating calculated data of the mid-infrared spectra with gas-volumetrically determined carbonate values and measurements of organic carbon from an elemental analyzer. For carbonate determination, this approach gave satisfying results. For measurements of organic carbon, it was necessary to discriminate into humus layers and mineral soils or even more groups to obtain satisfactory correlations between spectroscopically determined and conventionally measured values. These additional factors were the presence of carbonate, the forest type, and the dominant tree species. In mineral soils, fewer subdivisions were necessary to obtain useful results. In humus layers, groupings of sites with more similar characteristics had to be formed in order to obtain satisfying results. The conclusion is that the chemical background of soil organic matter leading to different proportions of functional groups, especially in the less humified organic matter of the humus layers, plays a key role in analyses with mid-infrared spectroscopy. Keeping this in mind, the present approach has a significant potential for the prediction of properties of forest soil layers, such as, e.g., carbonate and organic carbon contents.     

Quantitative determination of absolute organohalogen concentrations in environmental samples by X-ray absorption spectroscopy

An in situ procedure for quantifying total organic and inorganic Cl concentrations in environmental samples based on X-ray absorption near-edge structure (XANES) spectroscopy has been developed. Cl 1s XANES spectra reflect contributions from all Cl species present in a sample, providing a definitive measure of total Cl concentration in chemically heterogeneous samples. Spectral features near the Cl K-absorption edge provide detailed information about the bonding state of Cl, whereas the absolute fluorescence intensity of the spectra is directly proportional to total Cl concentration, allowing for simultaneous determination of Cl speciation and concentration in plant, soil, and natural water samples. Absolute Cl concentrations are obtained from Cl 1s XANES spectra using a series of Cl standards in a matrix of uniform bulk density. With the high sensitivity of synchrotron-based X-ray absorption spectroscopy, Cl concentration can be reliably measured down to the 5-10 ppm range in solid and liquid samples. Referencing the characteristic near-edge features of Cl in various model compounds, we can distinguish between inorganic chloride (Cl(inorg)) and organochlorine (Cl(org)), as well as between aliphatic Cl(org) and aromatic Cl(org), with uncertainties in the range of approximately 6%. In addition, total organic and inorganic Br concentrations in sediment samples are quantified using a combination of Br 1s XANES and X-ray fluorescence (XRF) spectroscopy. Br concentration is detected down to approximately 1 ppm by XRF, and Br 1s XANES spectra allow quantification of the Br(inorg) and Br(org) fractions. These procedures provide nondestructive, element-specific techniques for quantification of Cl and Br concentrations that preclude extensive sample preparation.     

Synthesizing a composite material of amorphous calcium carbonate and aspartic acid

A composite material of amorphous calcium carbonate and aspartic acid (Asp) was synthesized using a highly concentrated solution of calcium aspartate: a new approach. A transparent and amorphous solid with approximately 1 mm thickness was obtained. UV-vis transmittance spectrum of the composite shows no characteristic absorption in visible region. A Raman spectrum of the composite revealed a peak assigned to the symmetric stretching of carbonate ion. This study demonstrated that amorphous calcium carbonate could be stabilized using not only organic artificial macromolecules but also using Asp, a small biomolecule. This result is expected to engender development of new biomimetic materials.     

Molecular interactions alter clay and polymer structure in polymer clay nanocomposites.

In this work, using photoacoustic Fourier transform infrared spectroscopy (FTIR) we have studied the structural distortion of clay crystal structure in organically modified montmorillonite (OMMT) and polymer clay nanocomposites (PCN). To study the effect of organic modifiers on the distortion of crystal structure of clay, we have synthesized OMMTs and PCNs containing same polymer and clay but with three different organic modifiers (12-aminolauric acid, n-dodecylamine, and 1,12-diaminododecane), and conducted the FTIR study on these PCNs. Our previous molecular dynamics (MD) study on these PCNs reveals that significant nonbonded interactions (van der Waals, electrostatic interactions) exist between the different constituents (polymer, organic modifier, and clay) of nanocomposites. Previous work based on X-ray diffraction (XRD) and differential scanning calorimetry (DSC) on the same set of PCNs shows that crystallinity of polymer in PCNs have changed significantly in comparison to those in pristine polymer; and, the nonbonded interactions between different constituents of PCN are responsible for the change in crystal structure of polymer in PCN. In this work to evaluate the structural distortion of crystal structure of clay in OMMTs and PCNs, the positions of bands corresponding to different modes of vibration of Si-O bonds are determined from the deconvolution of broad Si-O bands in OMMTs and PCNs obtained from FTIR spectra. Intensity and area under the Si-O bands are indicative of orientation of clay crystal structures in OMMTs and PCNs. Significant changes in the Si-O bands are observed from each vibration mode in OMMTs and PCNs containing three different organic modifiers indicating that organic modifiers influence the structural orientation of silica tetrahedra in OMMTs and PCNs. Deconvolution of Si-O bands in OMMTs indicate a band at approximately 1200 cm(-1) that is orientation-dependent Si-O band. The specific changes in intensity and area under this band for OMMTs with three different organic modifiers further confirm the change in structural orientation of silica tetrahedra of OMMTs by organic modifiers. Thus, from our work it is evident that organic modifiers have significant influence on the structure of polymer and clay in PCNs. It appears that in nanocomposites, in addition to strong interactions at interfaces between constituents, the structure of different phases (clay and polymer) of PCN are also altered, which does not occur in conventional composite materials. Thus, the mechanisms governing composite action in nanocomposites are quite different from that of conventional macro composites.     

Development of attenuated total reflection based compression modulation step-scan Fourier transform infrared spectroscopy and its applications to rheo-spectral characterizations of polymer films

Dynamic compression modulation attenuated total reflection Fourier transform infrared (ATR FT-IR) spectroscopic methods have been developed in this paper for characterizing polymer films. To obtain dynamic compression polarized ATR spectra, internal reflection element (IRE) secure assemblies made of tungsten carbide with very high hardness (Knoop hardness of > 1000 kgf/mm(2)) have been designed. These assemblies are mounted on the Harrick Seagull ATR attachment and measured by step-scan FT-IR spectroscopy. The effect of static compression, air gaps, and refractive index changes were examined. Experimental and simulated results showed that the effect of air gaps between the sample and IRE and refractive index changes of the sample and IRE are negligible at values larger than a static torque of 40 cN m and good signal-to-noise ratios (SNR) and reproducible data can be obtained. Uniaxially and biaxially drawn poly(ethylene terephthalate) films were measured by the presented method. Both bipolar and unipolar bands were observed in the dynamic in-phase ATR spectra, which can be associated with their micro-structural environmental changes. This technique shows promise in evaluating various polymer film materials, including biaxially oriented films, multilayer coated film surfaces, and molecular interactions between polymer-polymer and polymer-additives at the film surface.     

Two-dimensional correlation study of uniaxially drawn poly(ethylene terephthalate) films by using attenuated total reflection based dynamic compression modulation step-scan fourier transform infrared in combination with spectral simulation analysis by density functional theory

Attenuated total reflection (ATR) based dynamic compression modulation two-dimensional (2D) correlation studies of uniaxially drawn poly(ethylene terephthalate) (PET) films have been performed in combination with spectral simulation analysis by density functional theory (DFT). The dynamic 2D infrared (IR) correlation spectra in the region of the CCO stretching mode vibrations show four distinct correlation peaks located around 1290, 1265, 1248, and 1234 cm(-1). These bands can be clearly assigned to the combination bands or coupling modes of the CH in-plane bend of the benzene ring or the CH(2) deformation of the ethylene glycol unit, as well as CCO stretching vibrations, which are gauche conformer's characteristic bands, by DFT analysis. The sequential analysis of 2D correlation data shows that, upon applying the dynamic compression, the response of the side chain regions (ester groups) occurs first, followed by that of the backbone regions (benzene rings). The ATR based dynamic compression modulation 2D correlation spectroscopy in combination with DFT analysis can be a powerful tool for various polymer characterizations.     

Impact of low molecular weight organic acids and dissolved organic matter on sorption and mobility of isoproturon in two soils

Isoproturon is a selective herbicide belonging to the phenylurea family and widely used for pre- and post-emergence control of annual weeds. Soil amendments (e.g. organic compounds or dissolved organic matter) may affect environmental behavior and bioavailability of pesticides. However, whether the physiochemical process of isoproturon in soils is affected by organic amendments and how it is affected in different soil types are unknown. To evaluate the impact of low molecular weight organic acids (LMWOA) and dissolved organic matter (DOM) on sorption/desorption and mobility of isoproturon in soils, comprehensive analyses were performed using two distinct soil types (Eutric gleysols and Hap udic cambisols). Our analysis revealed that adsorption of isoproturon in Eutric gleysols was depressed, and desorption and mobility of isoproturon were promoted in the presence of DOM and LMWOA. However, the opposite result was observed with Hap udic cambisols, suggesting that the soil type affected predominantly the physiochemical process. We also characterized differential components of the soils using three-dimensional excitation-emission matrix (EEM) fluorescence spectroscopy and Fourier transform infrared (FT-IR) spectroscopy and show that the two soils displayed different intensity of absorption bands for several functional groups.     

Influence of synthesis conditions on carbonate entrapment in perovskite SrSnO3

Strontium stannate (SrSnO₃), a perovskite material, was synthesized by the polymeric precursor method, with different routes to eliminate organic matter. The utilization of pure oxygen for the elimination of organic matter changed the Raman spectra, especially in the low frequency region. Some peaks, which were previously assigned to the perovskite phase, were not noticed when the carbonate amount was lower. On the other hand, the profile of the IR spectra and XRD patterns did not change. These results suggest that carbonate may be present inside the perovskite lattice.     

Effective path length in attenuated total reflection spectroscopy

Attenuated total reflection (ATR) spectroscopy is now the most popular sampling technique for the measurement of infrared spectra of condensed phase samples. Most practitioners of ATR spectroscopy use the equation for depth of penetration, d(p), to estimate the path length of the evanescent wave through the sample. However, the effective path length, d(e), of the evanescent wave in an ATR measurement, i.e., the equivalent path length in a transmission measurement that would lead to an absorption band of the same intensity, is a more accurate metric than d(p). In measurements designed to obtain the absorptivity of bands in the spectrum of a strongly absorbing viscous liquid, we have shown that the refractive index used in the expressions for d(e) must be modified to take into account the effect of anomalous dispersion before accurate effective path lengths and band absorptivities can be measured.