Traditional Wet Chemical Techniques Research Articles

Determination of hydroxyl groups in biorefinery resources via quantitative 31P NMR spectroscopy.

The analysis of chemical structural characteristics of biorefinery product streams (such as lignin and tannin) has advanced substantially over the past decade, with traditional wet-chemical techniques being replaced or supplemented by NMR methodologies. Quantitative 31P NMR spectroscopy is a promising technique for the analysis of hydroxyl groups because of its unique characterization capability and broad potential applicability across the biorefinery research community. This protocol describes procedures for (i) the preparation/solubilization of lignin and tannin, (ii) the phosphitylation of their hydroxyl groups, (iii) NMR acquisition details, and (iv) the ensuing data analyses and means to precisely calculate the content of the different types of hydroxyl groups. Compared with traditional wet-chemical techniques, the technique of quantitative 31P NMR spectroscopy offers unique advantages in measuring hydroxyl groups in a single spectrum with high signal resolution. The method provides complete quantitative information about the hydroxyl groups with small amounts of sample (~30 mg) within a relatively short experimental time (~30-120 min).

De symboliek van het snuffelen. Hoe een luchtverontreinigingsmonitor uitgroeide tot nationaal symbool

Recently, the Dutch national museum for the history of science and medicine, Museum Boerhaave in Leiden, acquired four air pollution monitors for its collection. These instruments were part of the Dutch national network for the measurement of air pollution, established in the 1970s. The monitors mark the transition in analytical chemistry from traditional wet-chemical techniques to the use of electronic and automatic tools. The significance of these instruments is not only scientific: they also played a social role. In the 1970s and 1980s, these air pollution monitors (popularly known as snuffelpalen (‘sniffer poles’) became a symbol for environmental worries and distrust with the political establishment, a trend we now consider as typical of that era.

Quantitative determination of cerium oxidation states in alkali-aluminosilicate glasses using M4,5-edge XANES

A calibration method for quantitative determination of Ce4+/Ce3+ in alkali-aluminosilicate glasses using Ce M4,5-edge X-ray absorption near edge structure (XANES) spectroscopy is presented. Samples of varying alkali oxide content synthesized over a range of temperatures and oxygen fugacities (fO2) were analyzed using both synchrotron-based XANES and traditional wet chemical techniques. Based on comparison to potentiometric determinations of Ce4+/Ce3+ in digested portions of our samples, Ce4+ was found to have a greater fluorescence yield (FLY) response to the incident radiation in the M4,5-edge XANES region than Ce3+. This results in an overestimation of the Ce4+/Ce3+ ratio when directly comparing the contributions of the two oxidation states to the total M-edge area, as has been used for crystalline materials. We offer a correction to M-edge determined Ce4+/Ce3+ ratios as follows:Ce4+/ΣCe=578.7Ce4+/ΣCe±5%XANESA±0.0040<Ce4+/ΣCe<0.4where the exponent A is a function of the number of non-bridging oxygens per tetrahedrally-coordinated cation (NBO/T) for a given glass composition, [Ce4+/ΣCe]XANES is the contribution from Ce4+ to the M4,5-edge area over the total area of the M4,5-edge, and Ce4+/ΣCe is the actual fraction of Ce4+ in the sample. The FLY response of Ce4+ was found to systematically increase with the degree of polymerization of the glass, suggesting that in addition to the local electronic environment, the FLY response of Ce is also dependent on longer range interactions.

An investigation of calibration materials for the measurement of metals in ambient particulate matter on filters by LA-ICP-MS

Three different types of simple and low-cost calibration material for the measurement of the metals content of ambient particulate matter (PM) on filters using laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) have been compared: cellulose ester filters spiked with multi-element calibration solutions, pellets of compressed ambient particulate matter certified reference material (CRM), and powdered ambient particulate matter CRM adhered to a surface. Elements determined were As, Cd, Cr, Cu, Fe, Mn, Ni, Pb, V and Zn, each at approximate levels of 1000 ng per filter. Blank filters spiked with multi-elemental standards were found to be significantly more reproducible and repeatable than materials based on powdered reference materials. However, a comparison of these spiked filters with real samples of ambient PM showed that the analytical sensitivities obtained per mass of analyte were significantly different. It is concluded that the spiked filters could act as very effective quality control standards correcting, to within 1%, drifts in LA-ICP-MS measurements of up to 10%, or as indirect calibration materials supported by additional measurements using traditional wet chemical techniques.

Bio-inspired synthesis of ZnO polyhedral single crystals under eggshell membrane direction

A simple and versatile technique was developed to prepare hierarchical ZnO single crystals by introducing eggshell membrane (ESM) to a bio-inspired approach. Based on the control of nucleation and gestation, ZnO nanocrystallites could grow at three dimensions into polyhedral single crystals through a surface sol-gel process followed by a calcination treatment. Different from traditional wet chemical techniques, our synthetic process depends more on the restrictive or directing functions of the ESM biomacromolecules. The hierarchical ZnO nanostructures doped with polyhedral single crystallites could be desirable for catalysts, photoelectrochemical devices, especially solar cells.

Use of near infrared spectroscopy to measure the chemical and mechanical properties of solid wood

Near infrared (NIR) spectroscopy (500 nm–2400 nm), coupled with multivariate analytic (MVA) statistical techniques, have been used to predict the chemical and mechanical properties of solid loblolly pine wood. The samples were selected from different radial locations and heights of three loblolly pine trees grown in Arkansas. The chemical composition and mechanical properties were measured with traditional wet chemical techniques and three point bending tests, respectively. The microfibril angle was measured with x-ray scattering. These chemical and mechanical properties were correlated with the NIR spectra using projection to latent structures (PLS) models. The correlations were very strong, with the correlation coefficients generally above 0.80. The mechanical properties could also be predicted using a reduced spectral range (650 nm–1150 nm) that should allow for field measurements of these properties using handheld NIR spectrometers.

Optical characteristics and color of TiN/SiN1.3 nanocomposite coatings

Decorative and protective coatings deposited by dry methods are very attractive due to the environmental restrictions on traditional wet chemical techniques. In this context, nanocomposite hard coatings were fabricated by plasma enhanced chemical vapor deposition from TiCl4/SiH4/N2/H2/Ar gas mixtures at substrate temperatures of 300 and 500 °C. Their optical characteristics such as refractive index, extinction coefficient, luminosity, and colors were quantitatively determined by spectroscopic ellipsometry and spectrophotometry. Pure TiN exhibited a metal-like behavior, and its optical properties were modeled by the Drude (free carrier) approach. Nanocomposite films consisting of about 5–10 nm size TiN grains incorporated in an amorphous SiN1.3 matrix were modeled by a sum of Drude and Lorentz (interband) transitions. Optical properties of the films were explained by their morphology and chemical structure, investigated by a multitechnique approach using scanning electron microscopy, transmission electron microscopy, elastic recoil detection in the time-of-flight regime, Auger electron spectroscopy, x-ray photoelectron spectroscopy, and Raman spectroscopy. Subsequent addition of Si to TiN caused a complex transformation from a polycrystalline to nanocomposite microstructure, which adopted a predominantly amorphous character. This was accompanied by a transition from a metallic to a dielectric behavior in terms of the optical response and electronic properties.

A new device for sampling small volumes of water from marine micro-environments

Recent developments in microelectrode technology provide more sensitive measurement of biologically relevant redox species and require less water than traditional wet chemical techniques. To fully exploit the power of this new technology, water samplers capable of collecting small volumes (1–10 ml) from discrete micro-environments were developed. We have designed a new, low-cost water sampler (SIPPER) to draw small volume water samples from discrete locations at deep-sea hydrothermal vents. The sampler successfully operated with the deep submergence vehicle (DSV) ALVIN at 2600 m depth to extract water samples from the fragile tube dwellings of a small polychaete. These samples were electrochemically analyzed on board ship for the presence of biologically important redox species inside the worm tube. Although designed specifically for this study, the sampler can be readily modified for application in a variety of disciplines requiring discrete samples within aquatic micro-environments.

Changes in organic structural group composition of humic and fulvic acids with depth in sediments from similar geographical but different depositional environments

A series of soil and swamp sediments from the Myall Lake National Park region, New South Wales, Australia have been studied by traditional wet chemical techniques and by solid state 13C NMR. Amino acid, carbohydrate, total acidity, phenolic, phenoxy and alkyl contents have been measured. Results obtained support previous literature reports that NMR carboxyl content measurements correlate better with total acidity than wet chemical COOH measurements. Large discrepancies (×20) between NMR and traditional chemical methods of measuring carbohydrate contents were also observed. The carbohydrate content of humic and fulvic acids measured by NMR or traditional methods drops rapidly with increasing soil or sediment depth probably because of metabolization by microorganisms. Fulvic acids contain more carboxylic acid and decreased alkyl carbon than their humic acid counterparts from the same source. The structure of humic acids however more closely reflect their depositional environment. For example, more phenolic and phenoxy carbon is present in forest humic acids because of the high lignin input.