near-IR Reflectance Spectroscopy Research Articles

Octahedral chemistry of 2:1 clay minerals and hydroxyl band position in the near-infrared: Application to Mars

With the arrival of Curiosity on Mars, the MSL has started its ground validation of some of the phyllosilicate characterization carried out with remote sensing near-IR spectroscopy from orbital instruments. However, given the limited range of action of the rover, phyllosilicate identification and characterization will have to rely mainly on orbital near-IR data. Investigation of Earth analogs can greatly assist interpretation of martian spectra and enable more robust analyses. In this contribution, Mg/Fe-rich clays from submarine hydrothermal origin that had been thoroughly characterized previously were investigated with near-IR reflectance spectroscopy. The clays are mixed-layer glauconite-nontronite, talc-nontronite, talc-saponite, and nontronite samples. The hydroxyl bands in the range 2.1–2.35 μm were decomposed into their several individual components to investigate correlations between the octahedral chemistry of the samples and the normalized intensity of several bands. Good correlations were found for the samples of exclusive dioctahedral character (glauconite-nontronite and nontronite), whereas poor or no correlations emerged for the samples with one (talc-nontronite) or two (talc-saponite) trioctahedral layer components, indicating a more complex spectral response. Because these bands analyzed are a combination of the fundamental OH stretching and OH bending vibrations, the response of these fundamental bands to octahedral chemistry was considered. For 2:1 dioctahedral phyllosilicates, Fe and Mg substitution for Al displaces both fundamental bands to lower wavenumbers (longer wavelengths), so that their effect on the position of the combination band is coherent. In contrast, for trioctahedral clays, Al and Fe 3+ substitution of octahedral Mg displaces the OH stretching band to lower wavenumber values, and the OH bending band to higher wavenumber values, resulting in partial or total mutual cancelation of their effects. As a result, clays with near-IR spectra indicating Mg-dominated octahedral compositions may in fact contain abundant Fe and some Al substitution. Thus, remote-sensing near-IR mineralogical and chemical identification of clays on Mars appears relatively straightforward for dioctahedral clay minerals but more problematic for trioctahedral clays, for which it may require a more detailed investigation of their near-IR spectra.

Development of Calibration Models for Rapid Determination of Chemical Composition of Pacific Oyster (Crassostrea gigas) by Near Infrared Reflectance Spectroscopy

ABSTRACT The feasibility for rapid determination of the chemical composition of Pacific oyster (Crassostrea gigas) by near IR reflectance spectroscopy (NIRS) was assessed. NIRS calibration models were developed using 118 sets of C. gigas samples (two to three sets per batch, total of 54 batches, 5–10 individuals per set) collected over 10 mo from seven coastal locations in northeast China. Glycogen, protein, fat, taurine, zinc, selenium, and ash contents of gonad-visceral mass and adductor muscle were analyzed by laboratory-based methods. Freeze-dried samples were scanned by NIRS at 10,000–4,000 cm-1 and their chemical composition was predicted by partial least squares regression. Results showed that the correlation coefficient of calibration (RC) was greater than 0.90 for most chemical components tested (except taurine, 0.8266). Similar differences were found in the correlation coefficient and other parameter indices in both cross and external validations for various chemical components. This study indic...

The use of near-infrared spectroscopy for the cure monitoring of an ethyl cyanoacrylate adhesive

Near-IR reflectance spectroscopy has been used to study the curing of ethyl cyanoacrylate adhesive on polished dental glass and microscope slide substrates. The effects of changing the glue film thickness and the type of substrate on the curing rate have been investigated whilst maintaining a constant humidity. The FTIR spectral data has been used to calculate and plot the extents of cure versus time for various film thicknesses.

Characterization of conichalcite by SEM, FTIR, Raman and electronic reflectance spectroscopy

AbstractThe mineral conichalcite from the western part of Bagdad mine, Bagdad, Eureka District, Yavapai County, Arizona, USA has been characterized by electronic, near-infrared (NIR), Raman and infrared (IR) spectroscopy. Scanning electron microscopy (SEM) images show that the mineral consists of bundles of fibres. Calculations based on the results of the energy dispersive X-ray analyses on a stoichiometric basis show the substitution of arsenate by 12 wt.% of phosphate in the mineral. Raman and IR bands are assigned in terms of the fundamental modes of AsO43− and PO43− molecules and are related to the mineral structure. Near-IR reflectance spectroscopy shows the presence of adsorbed water and hydroxyl units in the mineral. The Cu(II) coordination polyhedron in conichalcite can have at best pseudo-tetragonal geometry. The crystal field and tetragonal field parameters of the Cu(II) complex were calculated and found to agree well with the values reported for known tetragonal distortion octahedral complexes.

Spectroscopic characterization of chromite from the Moa-Baracoa Ophiolitic Massif, Cuba

The Cuban chromites with a spinel structure, FeCr 2O 4 have been studied using optical absorption and EPR spectroscopy. The spectral features in the electronic spectra are used to map the octahedral and tetrahedral co-ordinated cations. Bands due Cr 3+ and Fe 3+ ions could be distinguished from UV–vis spectrum. Chromite spectrum shows two spin allowed bands at 17390 and 23810 cm −1 due to Cr 3+ in octahedral field and they are assigned to 4A 2g(F) → 4T 2g(F) and 4A 2g(F) → 4T 1g(F) transitions. This is in conformity with the broad resonance of Cr 3+ observed from EPR spectrum at g = 1.903 and a weak signal at g = 3.861 confirms Fe 3+ impurity in the mineral. Bands of Fe 3+ ion in the optical spectrum at 13700, 18870 and 28570 cm −1 are attributed to 6A 1g(S) → 4T 1g(G), 6A 1g(S) → 4T 2g(G) and 6A 1g(S) → 4T 2g(P) transitions, respectively. Near-IR reflectance spectroscopy has been used effectively to show intense absorption bands caused by electronic spin allowed d -d transitions of Fe 2+ in tetrahedral symmetry, in the region 5000–4000 cm −1. The high frequency region (7500–6500 cm −1) is attributed to the overtones of hydroxyl stretching modes. Correlation between Raman spectral features and mineral chemistry are used to interpret the Raman data. The Raman spectrum of chromite shows three bands in the CrO stretching region at 730, 560 and 445 cm −1. The most intense peak at 730 cm −1 is identified as symmetric stretching vibrational mode, A 1g(ν 1) and the other two minor peaks at 560 and 445 cm −1 are assigned to F 2g(ν 4) and E g(ν 2) modes, respectively. Cation substitution in chromite results various changes both in Raman and IR spectra. In the low-wavenumber region of Raman spectrum a significant band at 250 cm −1 with a component at 218 cm −1 is attributed F 2g(ν 3) mode. The minor peaks at 195, 175, 160 cm −1 might be due to E g and F 2g symmetries. Broadening of the peak of A 1g mode and shifting of the peak to higher wavenumber observed as a result of increasing the proportion of Al 3+O 6. The presence of water in the mineral shows bands in the IR spectrum at 3550, 3425, 3295, 1630 and 1455 cm −1. The vibrational spectrum of chromite gives raise to four frequencies at 985, 770, 710 and 650 cm −1. The first two frequencies ν 1 and ν 2 are related to the lattice vibrations of octahedral groups. Due to the influence of tetrahedral bivalent cation, vibrational interactions occur between ν 3 and ν 4 and hence the low frequency bands, ν 3 and ν 4 correspond to complex vibrations involving both octahedral and tetrahedral cations simultaneously. Cr 3+ in Cuban natural chromites has highest CFSE (20,868 cm −1) when compared to other oxide minerals.

Near-infrared spectroscopy of stitchtite, iowaite, desautelsite and arsenate exchanged takovite and hydrotalcite

The hydrotalcite minerals stitchtite, iowaite and desautelsite together with the arsenate exchanged takovite and arsenate exchanged hydrotalcite have been studied using near-IR reflectance spectroscopy. Each mineral has its own characteristic NIR spectrum enabling recognition of the particular hydrotalcite. As such the technique has application in the field for the analysis and identification of hydrotalcites. Hydrotalcites have proven useful as an anion exchange material. Takovite and hydrotalcite were used to exchange carbonate anions by arsenate. Three Near-IR spectral regions are identified: (a) the high wavenumber region between 6400 and 7400 cm −1 attributed to the first overtone of the fundamental hydroxyl stretching mode, (b) the 4800–5400 cm −1 region attributed to water combination modes of the hydroxyl fundamentals of water, and (c) the 4000–4800 cm −1 region attributed to the combination of the stretching and deformation modes of the MOH units of the hydrotalcites. NIR spectroscopy enables the separation of the hydroxyl bands of the water and M–OH units for the hydrotalcites. Compared with the NIR spectroscopy of the structural units of the hydrotalcites namely gibbsite and brucite, the bands are broad.

Near-infrared spectroscopic study of nontronites and ferruginous smectite

The existence of life on planets such as Mars depend upon the presence of water. This water may not necessarily be as liquid or crystalline water but may be as interlayer water such as is found in smectitic clays. One group of smectites, relevant to the search for interplanetary life are those which have a high iron content, known as nontronites. Near-IR reflectance spectroscopy has been used to show the presence of water and hydroxyl units in these minerals. Three near-IR spectral regions are identified, (a) the high frequency region between 6400 and 7400 cm −1 attributed to the first overtone of the hydroxyl stretching mode; (b) the 4800–5400 cm −1 region attributed to water combination modes; and (c) the 4000–4800 cm −1 region attributed to the combination of the stretching and deformation modes of the FeFeOH units of nontronite. Two types of hydroxyl groups were identified using near-IR spectroscopy, hydroxyl units coordinated to the iron; and hydroxyl groups from water in the nontronite structure. The first hydroxyls are characterised by several bands, firstly in the 7055–7098 cm −1 region assigned to the first overtone of the AlFeOH stretching unit, secondly in the 6958–6878 cm −1 region attributed to the FeFeOH unit. The overtone of the hydroxyl stretching frequency of water was observed at around 6800 cm −1. These observations show that nontronites can be a source of water that may support life.

Application of Near-Infrared Spectroscopy to the Study of Alumina Phases

Near-infrared (IR) spectroscopy has been used to distinguish between alumina oxo and hydroxy phases. Two near-IR spectral regions are identified for this function: (1) the high-frequency region between 6400 and 7400 cm−1, attributed to the first overtone of the hydroxyl stretching mode, and (2) the 4000–4800 cm−1 region attributed to the combination of the stretching and deformation modes of the AlOH units. Near-IR spectroscopy allows the study and differentiation of the hydroxy and oxo(hydroxy) alumina phases, since each phase has its own characteristic spectrum. The spectrum of bayerite resembles that of gibbsite, whereas the spectrum of boehmite is similar to that of diaspore. Bayerite has four characteristic near-IR bands at 7218, 7128, 6996, and 6895 cm−1. Gibbsite shows five major bands at 7151, 7052, 6958, 6898, and 6845 cm−1. Boehmite displays three near-IR bands at 7152, 7065, and 6960 cm−1. Diaspore shows a prominent band at around 7176 cm−1. The use of near-IR reflectance spectroscopy to study alumina surfaces has a wide application, particularly with thin films and surfaces. The technique is rapid and accurate. Near-IR, because of its sensitivity, can be used in reflectance mode for the on-line processing of bauxitic minerals.

A Novel Silica Gel Adsorption/Near-Infrared Spectroscopic Method for the Determination of Hexanal as an Example of Volatile Compounds

The present research has demonstrated the feasibility of using silica gel adsorption/near-infrared (near-IR) reflectance spectroscopy to determine hexanal as an example of volatile compounds. Using...

Near-IR Reflectance Spectroscopy for the Determination of Motor Oil Contamination in Sandy Loam

We have investigated the application of near-IR reflectance spectroscopy to the determination of motor oil contamination in sandy loam. Although the present work is concerned with a specific case of contamination, we discuss the possibility of applying the method to other organic contaminants and other types of soil. The spectral region considered was 1600–1900 nm, which contains the first overtone of the CH stretch. Using a commercial Fourier transform spectrometer together with cross-validated partial least-squares data analysis, the one-sigma precision for the determination of motor oil in sandy loam was 0.17 wt % (0.13 to 0.26 wt % at the 95% confidence level). The largest contribution to the precision of the determination was sampling error, or inhomogeneity in each sample. Given the precision limit imposed by the sampling error, we found that the performance of the spectrometer could be lowered without affecting the overall precision. In a modeling exercise, adequate performance was obtained with a spectrometer having only seven spectral channels with a spectral resolution of 10 nm and a spectral noise level of 10−3 absorbance units. A design for an inexpensive miniature instrument is presented.

The use of NIRS to predict the chemical composition and the energy value of compound feeds for cattle

By means of a scanning monochromator and partial least-squares analysis, near-IR reflectance spectroscopy (NIRS) calibrations were developed to predict the chemical composition and the energy value of two different sets of compound feeds for cattle. The first set contained 179 compounds of heterogeneous nature, for which the energy value was calculated from in vivo digestibility. The second set consisted of 163 commercial dairy compounds for which the energy value was predicted from enzymatic digestibility. Spectral and reference data were highly correlated for all parameters, except for ash. For the first set, the root mean square error of prediction (RMSEP) amounted to 0.5% (percentage units) for moisture, 1.4% on dry matter basis (DM) for crude protein, 1.4% on DM for crude fibre, 0.7% on DM for crude fat, 2.1% for in vivo digestibility, 0.37 MJ kg −1 DM for metabolizable energy (ME) and 0.27 MJ kg −1 DM for net energy lactation (NEL). Prediction of ME and NEL with regression equations based on enzymatic digestibility was somewhat more accurate, with an RMSEP of 0.30 MJ kg −1 DM and 0.22 MJ kg −1 DM, respectively. For the more homogeneous second set, the RMSEP was lower for all parameters: 0.3% for moisture, 1.1% on DM for crude protein, 0.9% on DM for crude fibre, 0.3% on DM for crude fat, 1.3% for enzymatic digestibility, 0.30 MJ kg −1 DM for ME and 0.18 MJ kg −1 DM for NEL. It was proved that calibrations derived from energy values predicted from enzymatic digestibility were hardly less accurate than those derived from in vivo data. Calibrations based on the currently used NIRS instrument with 19 filters gave similar results to those based on the full spectrum for moisture, crude protein and crude fat, were less accurate for crude fibre, and clearly failed for energy evaluation. It was concluded that NIRS can be used as a screening method for the control of the chemical composition and the energy value of compound feeds for cattle.

Influence of wheat meal variability upon compacting behaviour during pelleting

The influence of wheat meal variability on its compacting behaviour has been studied. Seventeen samples of wheat, identified according to their origin and their supplier, were ground in the same conditions and characterised both by near-IR reflectance spectroscopy (NIRS) and a compression test. The NIRS technique was used to determine the chemical and particle size variability. A laboratory press was used to characterise the compacting behaviour of the meal. The study of the relationships between the variability and the compacting behaviour of the wheat meals has been performed by using a multivariate statistical treatment called canonical correlation analysis (CCA). The only chemical information that was highlighted by CCA was the water content. The water improved the meal compression by decreasing the force corresponding to the yield point of plasticity. The water influence has been observed from a low variation range of the moisture content (from 11 to 12.8%). Difference in particle size had no significant effect on the compacting behaviour.

Acidified Oxalate and Dithionite Solubility and Color of Synthetic, Partially Oxidized Al-Magnetites and Their Thermal Oxidation Products

AbstractSubmicron-sized (~3–60 nm) powders of Al-substituted magnetite were synthesized in the laboratory by precipitation methods by mixing appropriate molar volumes FeCl2, FeCl3 and AlCl3 solutions and precipitating with 20% NH4OH. Precipitates were dialyzed for 48 hr to remove excess salts and then freeze-dried. The nominal Al mole fractions [Als = Al/(Al + Fe)] in the initial precipitate ranged from 0.001 to 0.42. Portions of the resulting powders were heated sequentially in air at 400° and 500°C. Powders were examined using X-ray diffraction (XRD), transmission electron microscopy (TEM), and visible and near-IR reflectance spectroscopy. Solubilities were determined in ammonium oxalate (pH = 3) and dithionite-citrate-bicarbonate (DCB) solutions. As determined by XRD, the mineralogy of precipitated powder samples was predominantly magnetite. Powders having Als > 0.20 contained minor goethite and a poorly crystalline iron oxide phase (ferrihydrite?), and powders having Als > 0.25 also contained gibbsite. The color of the magnetites was black throughout the range of Al-substitution. Powders heated to 400°C were reddish brown; Munsell colors ranged from 5R 2/2 to 10R 3/4 for Als from 0.1–41.5%, respectively. By XRD, these powders were maghemite, but hematite was also detected by Mössbauer spectroscopy. XRD and Mössbauer data indicate powders heated to 500°C are hematite; their Munsell colors are not noticeably different from the corresponding 400°C samples. Mean crystallite dimensions (MCDs) of the magnetite powders increase with the Al mole fraction from ~10 nm for Als = 0.001% to a maximum value of 35 nm for Als = 0.15 and decrease slightly with further increasing Al substitution. Heating magnetite powders to 400°C did not change the MCDs significantly. Heating to 500°C resulted in hematites having MCDs larger than those for corresponding precursor magnetites for Als < 0.10. The opposite is true for hematites derived from magnetites having Als > 0.10. For hematite powders with Als > 0.05, MCD decreased with increasing Al-substitution. Solubilities of powders in oxalate solutions were independent of Al content and decreased in the order unheated samples (mostly magnetite) >400°C-heated samples (maghemite + hematite) >500°C-heated samples (hematite). All powders dissolved completely in DCB. The low crystallinity of the magnetite powders and the presence of ferrous iron are responsible for their relatively high solubility in oxalate solutions.

Procedures for processing cattle fecal samples for NIRS analysis

Factors related to and methods for processing cattle fecal samples for rapid analysis with near-IR reflectance spectroscopy (NIRS) for forage diet quality predictions were investigated. No differences ( P < 0.05) were found between mean prediction values for crude protein (CP) and 48-h in vitro digestible organic matter (IVDOM) for 1 and 4 h periods post-grinding. Sample hydration status, however, had a marked effect on predictions for both CP and IVDOM, indicating the necessity for control of sample moisture to obtain rapid and accurate analyses. Predictions for both CP and IV-DOM for microwave dried (MW) and forced-air oven dried (OD) samples were only slightly different in magnitude but differences were statistically significant using calibration equations developed from OD samples. These differences suggested the need for MW calibrations. Procedures for microwave drying and combined microwave and forced-air oven drying of cattle fecal samples were developed which resulted in NIRS calibrations which were statistically equivalent to calibrations with samples which had been dried in a forced-air oven.