Scanning Monochromator Research Articles

Mid- versus near Infrared Spectroscopic Analysis of Diversely Treated Feedstuffs

The objectives of this study were to determine the advantages and disadvantages of using mid-infrared diffuse reflectance spectroscopy versus near infrared for the analysis of diversely-treated forages and by-products, and to compare the relative merits of calibration development using multi-linear regression versus partial least squares regression for such samples. Study samples (325) were randomly selected from 2808 possible sample–treatment combinations generated using 18 feedstuffs, 26 treatments (acids, bases, oxidising and reducing agents, heat etc.), and six levels of reagent for each treatment. Neutral detergent fibre and crude protein were determined on all samples and calculated on an organic dry matter basis. Neat samples were scanned (256 co-added scans) from 4000 to 400 cm−1 at 4 and 16 cm−1 resolutions on a Fourier transform infrared spectrometer equipped with a sample transport device, and in the near infrared (1100–2498 nm) using a scanning monochromator (64 co-added scans). Calibration results using 4 cm−1 resolution mid-infrared spectra were equal to those obtained using near infrared spectra. While the results for both spectral regions using partial least squares regression were an improvement over those using multi-linear regression, neither region produced calibrations equal to those obtained for less diversely treated or non-treated samples. The results obtained also showed that: (1) visual determination of likely compositional or spectral outliers is not obviously feasible using either near or mid-infrared spectra; (2) changes in spectra due to treatment can be much more easily attributed to compositional components using mid- as opposed to near infrared spectra; (3) examination of either mid-infrared PLS or PCR factors can be useful in determining compositional changes caused by treatments, while near infrared PLS and PCR factors appear to be dominated by moisture differences.

The Development of near Infrared Reflectance Spectroscopy Calibrations for Undried Grass Silage and Their Transfer to Another Instrument Using Multiple and Single Sample Standardisation

This study was undertaken to explore the possibility of developing accurate, robust near infrared (NIR) spectroscopy calibrations for undried grass silage (a very heterogeneous, high moisture forage) without costly or lengthy pre-treatment of the sample. This was achieved by scanning a large surface area of the sample using a coarse transport cell in conjunction with a Foss NIRSystems 6500 scanning monochromator, which moves the sample vertically past the light source. Equations were produced for alcohol corrected toluene dry matter, pH, N2, neutral detergent fibre, acid detergent fibre, D-value (digestible organic matter in the dry matter) and potential metabolic intake with accuracy comparable to finely comminuted undried grass silage. The second objective of this study was to examine the possibility of transferring the undried grass silage calibrations developed on the 6500 spectrophotometer across NIR instruments and cell types. The cloning technique of Shenk was used to match spectrally the 6500 spectrophotometer and a Foss NIRSystems 5000 NIR spectrophotometer. Seventy undried grass silage samples, typical of the calibration set, were scanned through both instruments using a coarse transport cell and a natural product cell. Cloning was based on (a) 30 samples and (b) one central sample. Standardisation files were produced (using the ISI software) and applied to the spectra of the remaining 40 validation samples, scanned on the 5000 spectrophotometer (regarded as the slave instrument). These standardised spectra were predicted by the master equations developed on the 6500 instrument and the results compared to the corresponding master validation spectra ( n = 40) scanned in the coarse transport cell and predicted by the master equations (regarded as the reference values). An alternative approach of standardising the master calibration set spectra, to look like they were scanned in a natural product cell and rerunning the calibrations, was also performed and the master natural product spectra predicted using the new natural product equations and compared to the reference values. In all instances, this cloning technique proved very successful, clearly indicating that undried grass silage calibrations can be transferred across these NIR instruments with little loss in accuracy of prediction.

A pulsed Grimm glow discharge as an atomic emission source

A high voltage, microsecond regime pulse dc glow discharge was applied to a standard Grimm source on a modified LECO SA-2000 direct reader spectrometer and to a duplicate Grimm source coupled to a scanning monochromator. The effects of experimental conditions, including pulse voltage, pulse frequency, pulse width and Ar pressure, on Cu atomic and ionic emission intensities were examined and compared with continuous discharge results. The pulsed Grimm source has a higher sputtering rate, greater signal intensity and lower detection limits. The pulsed signal for atomic lines shows a different temporal response from ionic lines. Pulsed Grimm GD-AES also offers control features advantageous in the measurement of thin surface layers.

Prediction of Leaf:Stem Ratio in Grasses Using near Infrared Reflectance Spectroscopy

Leaf:stem ratio of grass stands is an important factor affecting diet selection, quality, and forage intake. Estimates of leaf:stem ratios commonly are based on a labor intensive process of hand separating leaf and stem fractions. Near infrared reflectance spectroscopy (NIRS) has been used successfully to predict forage quality and botanical composition of vegetation samples. The objective of this study was to evaluate the use of NIRS to predict leaf:stem ratios in big bluestem (Andropogon gerardii Vitman), switchgrass (Panicum virgatum L.), and smooth bromegrass (Bromus inermis Leyss.). A total of 72 hand-clipped samples of each species was taken from seeded monocultures in eastern Nebraska throughout the 1992, 1993, and 1994 growing seasons. Leaf:stem ratio was determined first for each sample and then the entire sample was ground. Samples were scanned by a Perstorp model 6500 near infrared scanning monochromator. Three calibration equations were developed based on using 18, 36, and 54 (1/4, 1/2, and 3/4 of total samples, respectively) samples. These 3 calibration equations were used to determine the number of samples necessary to achieve an r2 of 0.70 or higher for each data set. Big bluestem and switchgrass had coefficients of determination (r2) of less than or greater than 0.69 for all calibration equations except for the equation using only 18 samples of big bluestem r2 = 0.60). Smooth bromegrass had a r2 ranging from only 0.06 to 0.14 for the calibration equations regardless of the number of samples used. Near infrared reflectance spectroscopy was a rapid means of estimating leaf:stem ratios in monocultures of big bluestem and switchgrass but it was not suitable for smooth bromegrass.

A PC Interface for a Single-Ratio Stepper Motor

A very simple stepper motor controller was designed and built for a scanning monochromator. The circuit design centers around a programmable peripheral interface chip that controls the gate of four power transistors, which in turn activate the coils on the stepper motor. Besides being very inexpensive to build, the interface shows improved performance when compared to the commercially available controller.

Prediction of Total Dietary Fiber by Near-Infrared Reflectance Spectroscopy in High-Fat- and High-Sugar-Containing Cereal Products

The near-infrared (NIR) spectral properties of cereal products containing high fat or high sugar can differ substantially from the spectral properties of other cereal products. An existing NIR model, using preprocessed reflectance spectra and partial least-squares analysis, for the prediction of total dietary fiber in cereal products was expanded to two new models called (1) the “fat-expanded” model and (2) the “fat- and sugar-expanded” model. The fat-expanded model enlarges the existing model with high-fat-content products as calibration samples, and the “fat- and sugar- expanded” model also includes products with high sugar and high crystalline sugar content. The dry milled cereal and grain products were analyzed in the laboratory according to AOAC method 991.43 for the determination of total dietary fiber, and NIR reflectance spectra were collected with a scanning monochromator. Data analysis and selection of representative high-fat and high-sugar samples were performed with a commercial analysis program. The two expanded models had standard errors of cross-validation and R2 similar to those of the existing model, with acceptable standard error of performance and r2 when tested with independent validation samples. The existing model was, thus, expanded to include high-fat, high-sugar, and high crystalline sugar cereal products while maintaining prediction accuracy. Keywords: Dietary fiber; near-infrared; chemometrics; cereal

The Use of near Infrared Reflectance Spectroscopy to Predict the Insoluble Dietary Fibre Fraction of Cereal Products

The insoluble and soluble fractions of dietary fibre have different human physiological effects and their presence in foods is of interest to consumers, the medical community and the cereal product industry. The development of a model, using near infrared (NIR) reflectance spectroscopy, to predict insoluble dietary fibre in a wide range of dry-milled cereal products and grains is described. The products included breakfast cereals, crackers, brans, pastas and flours. Insoluble dietary fibre was measured by the AOAC enzymatic–gravimetric procedure (AOAC 991.43). The range in insoluble dietary fibre was 0–48%. Near infrared reflectance spectra were obtained with a scanning monochromator and data analysed with a commercial analysis program. A calibration ( n = 90) was developed for prediction of insoluble dietary fibre using preprocessed spectra and modified partial least squares regression. The standard error of cross validation and R2 were 1.34% and 0.99, respectively. The model was tested with independent validation samples ( n = 32) and the resulting standard error of performance and r2 were 1.13% insoluble dietary fibre and 0.99, respectively. The results show that NIR spectroscopy can be used to predict the insoluble dietary fibre content in a wide variety of processed and unprocessed cereal products.

Modelling near infrared instrument differences by chemometric methods: testing for near infrared forage analysis

The possibilities of using the two-block Partial Least Squares (PLS2) method to allow the standardization between the spectra of forage measured in different types of Near Infrared (NIR) instruments, tilting filters and scanning monochromators, are presented. Procedures are developed to transfer spectra from one instrument to another in a network of instruments of different types. PLS1 plus repeatability control is used to build a calibration equation of the network which minimizes the influence of the spectral residuals (remaining after standardization) on the predicted concentrations among the standardized instruments. The validation of the standardization matrix is obtained from representative samples (feed and raw materials) used as standards — yielding a general external validation — or from real samples of Catalonian origin — yielding a specific external validation. With the proposed procedures, the repeatability of concentration measurements among instruments is improved and the number of reference analysis needed is decreased. The possibility is afforded for instruments of lower resolution (e.g., tilting-filter instruments) to participate in the same network as higher resolution instruments (e.g. monochromators) taking advantage of the calibration spectra measured in the latter.

Determination of Protein in Ground Wheat Samples by Mid-Infrared Diffuse Reflectance Spectroscopy

The objective of this study was to determine whether mid-infrared diffuse reflectance spectroscopy could be used in the same manner as near-infrared diffuse reflectance spectroscopy to quantitatively determine the protein content of ground wheat samples. One hundred and thirty hard red winter wheat samples were assayed for protein by combustion and scanned in the near- and mid-infrared. Samples (UDY ground) were scanned neat in the near-infrared from 1100 nm (9091 cm−1) to 2498 nm (4003 cm−1) on a scanning monochromator and in the mid-infrared from 4000 cm−1 (2500 nm) to 400 cm−1 (25,000 nm) on a Fourier transform spectrometer at 4-and 16-cm−1 resolutions. Protein content varied from a low of 8.98% to a high of 18.70% (average of 12.86% with a standard deviation of 1.66%). Calibrations developed with the use of partial least-squares gave an R2 and bias-corrected standard error of performance of 0.999 and 0.054 for the near-infrared and 0.997 and 0.085 for the mid-infrared (4 cm−1 resolution). Calibration results based on mid-infrared spectra, while not as good as those for near-infrared spectra, were nevertheless quite good. These results demonstrate that it is possible to develop satisfactory calibrations for protein in ground wheat with the use of mid-infrared spectra without the need for sample dilution with KBr.

A multi-mode extrinsic Fabry - Pérot interferometric strain sensor

This paper reports on the fabrication and evaluation of a multi-mode extrinsic Fabry - Pérot interferometric (EFPI) sensor which is capable of measuring both tensile and compressive strains. A scanning monochromator was used to measure the absolute cavity length of the EFPI sensor. Sensors of this type were embedded within a 16-ply carbon-fibre-reinforced epoxy composite and tested under quasi-static tensile and compressive loading conditions. Excellent correlation was observed between the EFPI sensor and a surface-mounted extensometer. The sensor system can operate in the strain range from -1 to 1% with an accuracy of better than 30 micro-strain. Preliminary results indicated that the sensor design was relatively insensitive to temperature in the range 38 - 180 . An analysis of the relationship between the insensitivity and the sensor geometry is also presented.

Comparison of direct current and radio frequency argon magnetron discharges by optical emission and absorption spectroscopy

A magnetron sputtering discharge is studied by optical emission and absorption spectroscopy, following an experimental design procedure. The 33-mm-diam target is made in an aluminium base alloy. The radiation is focused on an optical fiber and is spectrally analyzed in a Jobin–Yvon computer-controlled 1.0 m Czerny–Turner scanning monochromator. The spatial resolution is 2 mm. Emission line intensities from the Ar sputtering gas and the sputtered species are studied as a function of geometrical and physical discharge parameters: excitation mode (rf or dc), target thickness, gas discharge pressure, electric power (rf) or current (dc), and the distance from the target. In emission spectroscopy, two Ar I lines are studied: Ar I 425.9 nm 3p55p(3p1)−3p54s(1s2) and Ar I 451.1 nm 3p55p(3p5)−3p54s(1s2) and also an Ar II line 442.6 nm 3p44p(4D0)−3p44s(4P). The first excited level configuration of Ar (3p54s) contains two metastable (1s5,1s3) and two resonant (1s4,1s2) levels. The Al excited and ground states have also been analyzed: the Al I 3p2P0−4s2S and Al I 3p2P0−4s2S. By use of hollow-cathode lamps, absorption due to aluminum atoms and argon metastable and resonant atom states densities are evaluated, as a function of the same parameters as in emission. The experimental responses (emission and absorption intensities) are fitted by a quadratic equation in which interactions between factors are included. The influences of the main factors are deduced and discussed.

Mass Ratio of the Deuteron and Proton from the Balmer Spectrum of Hydrogen: Variation on an Undergraduate Physical Chemistry Experiment

A common experiment in some Physical Chemistry Laboratory courses involves the analysis of the Balmer series of the hydrogen atom to derive the Rydberg constant. We describe a simple modification of this experiment, which involves a comparison of the Balmer spectrum of hydrogen and deuteron atoms to determine their nuclear mass ratio. The accuracy of the experiment relies on a sufficient amount of 1H2 being present along with 2H2 in the deuterium lamp for its use as an internal standard. In our implementation, we use a gear-driven 0.25 m scanning monochromator with a 1200 lines/mm grating. The typical precision of our measured mass ratio is better than 10 %.

Polarized hyper-Rayleigh light scattering measurements of nonlinear optical chromophores

Hyper-Rayleigh light scattering measurements at incident wavelengths of 1064 and 1319 nm are reported for several organic nonlinear optical chromophores in solution with approximately 5%–10% uncertainty in the relative first hyperpolarizabilities. The measured chromophores include representatives from C1, Cs, C2V, and D3 molecular point groups and include both neutral and ionic compounds. The measurements were made with 2–5 cm−1 spectral resolution and include polarization analysis of the incident and scattered light. Polarization ratios were measured with 2%–3% uncertainty for each molecule, and relative magnitudes of the hyperpolarizability components were deduced. Two-photon induced fluorescence from several chromophores was observed to overlap with the scattered second harmonic light spectrum. The use of a scanning monochromator, however, generally allows the separation of these two sources of photons. The measured first hyperpolarizabilities are consistent with previous electric field induced second harmonic generation measurements of the same compounds, provided that the standard reference value for the nonlinear susceptibility of quartz is taken to be d11=0.30±0.02 pm/V at 1064 nm.

A sagittal focusing and scanning monochromator for 8–80 keV synchrotron radiation at DORIS III

A sagittal focusing and scanning monochromator for 8–80 keV synchrotron radiation at DORIS III

A photon counting dynamic digital lock-in amplifier for background suppression in glow discharge atomic emission spectrometry

A photon counting dynamic digital lock-in amplifier, (PC-DDLIA), has been developed for the suppression of Ar lines in glow discharge lamp atomic emission spectrometry, (GDL-AES). The experimental set-up consists of a Grimm-type GDL, a prism-type scanning monochromator, photon counting electronics, an Apple Ile computer with an interface card and a computer controllable high voltage power supply. The photon counting electronics are designed to convert the photon pulses to logic pulses. A discriminator is used to reject pulses below a threshold level. The high voltage power supply is modulated with a square waveform generated from DAC and photon pulses are counted synchronously by the timer/counter chip, versatile interface adaptor (VIA-6522) on the interface card of computer. The data are analyzed in two steps. In the “learn mode”, the GDL is modulated with a square waveform between 370 and 670 V and two spectra consisting of only Ar lines are obtained in a spectral window between 287.1 and 290.0 nm. A new modulation waveform is computed from these spectra which yields two overlapped spectra when the PC-DDLIA is scanned over the same spectral window. In the “analysis mode” of data acquisition, a target material with the analyte element(s) in it is used and the spectrometer is scanned with a dynamically varying rectangular waveform over the same spectral window. The net spectrum consists of pure atomic lines free from any Ar lines. The detection limit for the determination of Si (288.2 nm) in the presence of interfering Ar lines (288.1 and 288.4 nm) is found to be 0.083%, whereas suppression of Ar lines over the same spectral window lowers the detection limit to 0.013%.

Reduction of the background thermal radiation input to a cryogenic radiometer for the measurement of a spectrally filtered continuum source

An optical system is proposed that reduces the background thermal radiation input to a cryogenic radiometer by a factor of almost 40000. This system is based on a concave grating which can be configured to create a scanning monochromator with the cryogenic radiometer entrance aperture as the exit slit. A cryogenic radiometer is described that has a sensitivity of 1 pW and which is suitable for use with this monochromator and a continuum source to calibrate detectors at an uncertainty level of one part in 105.

Observations on Determination of Dysprosium in Labeled Digesta Samples by Near Infrared Spectroscopy

The objective of this work was to determine whether the Dy content of ruminal digesta samples labeled by pulsedosing intra-ruminally with Dy-labeled forages could be determined by near infrared reflectance spectroscopy. Ruminal grab samples were obtained from four steers. Equal numbers of alfalfa and orchardgrass samples were collected at 17 times (0 to 165h) after dosing and analyzed (total of 272 samples). Dysprosium was determined by direct current plasma emission spectrometry. Spectra were obtained by scanning ground samples on a scanning monochromator. Calibrations for Dy (0 to 349.5ppm; mean = 44.5ppm) were carried out using both step-wise and partial least squares regressions. Wavelength selections using step-wise regression included characteristic Dy wavelengths and resulted in R2 and standard error of analysis of ∼.9 and ≥20ppm, respectively. Partial least squares regressions, although more robust, were not significantly better. Sample ashing to increase relative Dy concentrations did not improve the results. Further investigations indicated that interference by Co marker, also present in the samples, was a problem. Although near infrared reflectance spectroscopy is capable of determining Dy in labeled forages, further work is needed to increase its accuracy.

Optical teat inspection for automatic milking systems

Automatic milking systems require methods of ensuring that cows are clean before milking. This paper investigates the feasibility of a sensor to detect dirt on a teat based on the optical reflectivity of the teat. A fibre optic sensor and fast scanning monochromator were used to make a series of measurements of the visible and near infrared reflectance properties of teats and the major surface contaminants. From these data spectral features, which uniquely corresponded to manure and blood on a clean teat, were identified.

A cryogenically cooled, sagittal focusing scanning monochromator for ESRF

A double crystal monochromator for fast scans over large energy ranges has been designed, constructed, and tested at ESRF. The instrument is based on a drive unit operated in air that rotates a large wheel sitting in UHV and supporting the two crystal assemblies. The link between the drive and the wheel is realized by a differentially pumped feedthrough. In order to withstand the full power of typical ESRF undulators without noticeable deformation, the first crystal is cooled by liquid nitrogen via pipes located in the hollow core of the differentially pumped feedthrough. The second crystal mount is based on an elastically deformable structure driven by piezoelectric and pneumatic actuators for precise angular adjustments. In its basic version the relative distance between the first and second crystal is kept constant (channel cut type of design), but a nearly fixed beam at the focal plane can be obtained, as the Bragg angle is changed, by the partial compensation of two different effects: the vertical displacement of the exit beam typical of channel cut designs and its divergence with respect to the incoming one due to the difference in lattice spacing between the first cooled crystal and the second one at room temperature. Horizontal focusing of the beam is achieved by sagittal bending of the second crystal. The major drawbacks of crystal focusing, the necessity of changing the radius of curvature while scanning, and the losses in throughput due to the anticlastic deformation experienced at high energy are circumvented by an appropriate choice of the crystal geometry and orientation.

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.