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March 2015 


Submitted Papers


Comparative-Discrimination Spectral Detection Method for the Identification of Vapors Using Overlapping Broad Spectral Filters

            Menelaos K. Poutous, Kevin J. Major, Kenneth J. Ewing, Jas Sanghera,

   Ishwar D. Aggarwal


We present a comparative-discrimination spectral detection approach for the identification of chemical vapors using broad spectral filters. We applied the method to flowing vapors of as received and non-interacting mixtures for the detection of the volatile components of a target chemical in the presence of interferents. The method is based on measurements of the overall spectral signature of the vapors, where the interferent spectrum largely overlaps the target spectrum. In this work we outline the construction of a set of abstract configuration-space vectors, generated by the broadband spectral components from sampled chemical vapors, and the subsequent vector-space operations between them, which enable the detection of a target chemical by comparative discrimination from interferents. The method was applied to the C–H vibrational band from 2500 to 3500 cm-1, where there is large spectral signal overlap between the chosen target chemical and two interferents. Our results show clear detection and distinction of the target vapors without ambiguity.


Keywords: Filter photometry; IR spectroscopy; Infrared spectroscopy; Comparative-discrimination spectral detection; Overlapping spectral absorption signal; Broad spectral filters.



Independent Component Analysis-­Based Algorithm for Automatic Identification of Raman Spectra of Artistic Pigments and Pigment Mixtures

Juan José Gonzalez-Vidal, Rosanna Pérez Pueyo, Maria Jose Soneira, 

Sergio Ruiz-­Moreno


A new method has been developed to automatically identify Raman spectra, whether they correspond to single- or multicomponent spectra. The method requires no user input or judgment. There are thus no parameters to be tweaked. Furthermore, it provides a reliability factor on the resulting identification, with the aim of becoming a useful support tool for the analyst in the decision making process. The method relies on the multivariate techniques of principal component analysis (PCA) and independent component analysis (ICA), and on some metrics. It has been developed for the application of automated spectral analysis, where the analyzed spectrum is provided by a spectrometer that has no previous knowledge of the analyzed sample, meaning that the number of components in the sample is unknown. We describe the details of this method and demonstrate its efficiency by identifying both simulated spectra and real spectra. The method has been applied to artistic pigment identification. The reliable and consistent results that were obtained make the methodology a helpful tool suitable for the identification of pigments in artwork or in paint in general.


Keywords: Raman spectroscopy; Pigment identification; Pigment mixtures; Multicomponent analysis; Principal component analysis; Independent component analysis.



Fluorescence Spectroscopy in Process Analytical Technology (PAT): 

Simultaneous Quantification of Two Active Pharmaceutical Ingredients in a Tablet Formulation

            Solveig Warnecke, Åsmund Rinnan, Morten Allesø, Søren B.Engelsen


Many pharmaceuticals include highly potent active pharmaceutical ingredients (API), which only require a small dosage to obtain the desired therapeutic effect. This leads to a challenge for quantification of the API using process analytical technology, since the standard nondestructive measurement technique, near-infrared spectroscopy, is not able to quantify below 1% (weight/weight (w/w)) API content. In formulations with more than one API, this challenge is further increased. The purpose of this study is to scrutinize the potential of fluorescence spectroscopy for the simultaneous quantification of two APIs: flupentixol (FLU) in low dosage (0.208–0.625% w/w free base) and melitracen (MEL) (4.17–12.5% w/w free base) in a tablet formulation. Despite internal quenching between the ingredients and the two APIs, this paper demonstrates that it is possible to establish calibrations using partial least squares (PLS) regression on unfolded fluorescence landscapes with a root mean square error of prediction and relative error of 0.038% (w/w) and 9.1%, for FLU and 0.344% (w/w) and 4.1% for MEL, respectively.


Keywords: Fluorescence spectroscopy; API; Flupentixol; Melitracen; Partial least squares regression; PLS; Quenching.




Measurements of Metal Alkylamide Density During Atomic Layer Deposition Using a Mid-Infrared Light Emitting Diode (LED) Source

 James E. Maslar, John Hoang, William A. Kimes, Brent A. Sperling


A nondispersive infrared (NDIR) gas analyzer that utilizes a midinfrared light emitting diode (LED) source was demonstrated for monitoring the metal alkylamide compound tetrakis(dimethylamido) titanium (TDMAT), Ti[N(CH3)2]4. This NDIR gas analyzer was based on direct absorption measurement of TDMAT vapor in the C–H stretching spectral region, a spectral region accessed using a LED with a nominal emission center wavelength of 3.65 μm. The sensitivity of this technique to TDMAT was determined by comparing the absorbance measured using this technique to the TDMAT density as determined using in situ Fourier transform IR (FT-IR) spectroscopy. Fourier transform IR spectroscopy was employed because this technique could be used (1) to quantify TDMAT density in the presence of a carrier gas (the presence of which precludes the use of a capacitance manometer to establish TDMAT density) and (2) to distinguish between TDMAT and other gas-phase species containing IR-active C–H stretching modes (allowing separation of the signal from the LED-based optical system into fractions due to TDMAT and other species, when necessary). During TDMAT-only delivery, i.e. in the absence of coreactants and deposition products, TDMAT minimum detectable molecular densities as low as ≈4 x 1012 cm-3 were demonstrated, with short measurement times and appropriate signal averaging. Reactions involving TDMAT often result in the evolution of the reaction product dimethylamine (DMA), both as a thermal decomposition product in a TDMAT ampoule and as a deposition reaction product in the deposition chamber. Hence, the presence of DMA represents a significant potential interference for this technique, and therefore, the sensitivity of this technique to DMA was also determined by measuring DMA absorbance as a function of pressure. The ratio of the TDMAT sensitivity to the DMA sensitivity was determined to be 6.0. To further examine the selectivity of this technique, measurements were also performed during atomic layer deposition (ALD) of titanium dioxide using TDMAT and water.During ALD, potential interferences were expected from the evolution of DMA due to deposition reactions and the deposition on the windows of species containing IR-active C–H stretching modes. It was found that the interfering effects of the evolution of DMA and deposition of species on the windows corresponded to a maximum of only ≈6% of the total observed TDMAT density. However, this level of interference likely is relatively low compared to a typical chemical vapor deposition process in which coreactants are introduced into the chamber at the same time.


Keywords: Atomic layer deposition; ALD; Infrared absorption; Light emitting diode; LED; Metal alkylamide; Nondispersive infrared gas analyzer; NDIR; Tetrakis(dimethylamido) titanium; TDMAT.




Forearm Deoxygenation Measured by NIRS Using a Handgrip Test in Mitochondrial Myopathy

Bert M. Celie, Jan Boone, Joél E. Smet, Arnaud V. Vanlander, Jan L. De Bleecker,

Rudy N. Van Coster, Jan G. Bourgois



The purpose of this paper is to test whether peripheral oxygenation responses measured with near-infrared spectroscopy (NIRS) would differ between patients suffering from mitochondrial myopathy (MM) and healthy controls during an incremental handgrip exercise test. Two groups of subjects were studied: 11 patients with MM and 11 age- and gender-matched untrained healthy controls. A handgrip exercise until exhaustion protocol was used consisting of 2 min periods of work ( Hz) at different intensities, separated by a 60 s rest period. The changes in deoxyhemoglobin and deoxymyoglobin (deoxy[Hb + Mb]) during each work step were expressed in percent to the maximum deoxy[Hb + Mb]-value measured during arterial occlusion in forearm muscles. A repeated measures analysis of variance was used to compare the increase in deoxy[Hb + Mb] between MM patients and controls with increasing intensity.Statistical analysis revealed a significant difference between both populations (P < 0.001) indicating that the increase in deoxy[Hb + Mb] showed a significantly different pattern in the two populations. In the post hoc analysis significant lower deoxy[Hb + Mb] -values were found for MM patients at every intensity. The results of this paper show significantly different skeletal muscle oxygenation responses, measured with an optical method as NIRS, between MM patients and age- and gender-matched healthy subjects at submaximal and maximal level during an incremental handgrip exercise. This optical method is thus a valuable tool to assess differences in peripheral oxygenation. Moreover, this method could be used as an evaluation tool for follow up in interventional pharmacological studies and rehabilitation programs.


Keywords: Near infrared spectroscopy; NIRS; Mitochondrial dysfunction; Handgrip exercise; Peripheral oxygenation.



Determination of Spectroscopic Band Shapes by Second Derivatives.

Part I-Theory

            Jean‐Joseph Max, Camille Chapados


The molecular spectra of water, aqueous solutions, hydrogen bonded systems, and others have massive bands that contain many overlapping components. To decipher the spectra for molecular interpretation, it is necessary to separate these. Several attempts to do this have been made without clear success. To surmount some of the difficulties, we present a novel method, which consists of quantitatively evaluating the spectral band second-derivative profiles. This aids in the determination of the original band profiles: Gaussian, Lorentzian (Cauchy), and Gauss–Lorentz products. Then the number of components in a massive absorption, their shapes, and their positions can be determined. We tested the usefulness of the method in the visible region using calibration standards: a light emitting diode emission spectrum and a holmium chloride (HoCl2) solution. To verify its utility in the infrared region, we used liquid propanol, liquid acetonitrile, and aqueous acetone.

Derivative spectroscopy; Attentuated total reflection infrared spectroscopy; ATR-IR spectroscopy; Aqueous solutions; Gaussian profile; Lorentzian profile; Gauss–Lorentz product profile; Propanol; Acetonitrile; Acetone.



Optical Detection of Tracer Species in Strongly Scattering Media 

            Eric M. Brauser, Peter E. Rose, John D. McLennan, Michael H. Bartl


A combination of optical absorption and scattering is used to detect tracer species in a strongly scattering medium. An optical setup was developed, consisting of a dual-beam scattering detection scheme in which sample scattering beam overlaps with the characteristic absorption feature of quantum dot tracer species, while the reference scattering beam is outside any absorption features of the tracer. This scheme was successfully tested in engineered breakthrough tests typical of wastewater and subsurface fluid analysis, as well as in batch analysis of oil and gas reservoir fluids and biological samples. Tracers were detected even under highly scattering conditions, conditions in which conventional absorption or fluorescence methods failed.

Keywords: Fluorescence; Nanocrystals; Tracers; Turbidity; Light scattering; Light absorbance.




Determination of Copper and Zinc Pollutants in Ludwigia Prostrata Roxb Using Near Infrared Reflectance Spectroscopy

            Aiguo Ouyang, Lixia Jiang, Yande Liu, Yong Hao, Bingbing He


The feasibility of using near-infrared reflectance spectroscopy (NIRS) to determine the concentrations of copper (Cu) and zinc (Zn) in Ludwigia prostrata Roxb plants was investigated. Ludwigia prostrata Roxb plants were grown over a full growth cycle undercontrolled laboratory conditions in soils contaminated with heavy metals. The Cu and Zn concentrations in 72 L. prostrata Roxb samples were analyzed using flame atomic absorption spectrometry, and NIRS spectra were collected in the 1099–2500 nm range. Five mathematical treatments of the spectral data were compared prior to developing the calibration models (n = 48) using partial least squares regression methods. The two calibration models for Cu and Zn concentrations were evaluated according to the correlation coefficient of cross-validation (Rcv) and root mean squares error of cross-validation. The highest Rcv and the lowest RMSECV were obtained for Cu (0.9 and 7.24 mg kg-1) and Zn (0.94 and 19.17 mg kg-1), respectively. The results showed that near infrared diffuse reflectance spectroscopy can be used for the rapid determination of Cu and Zn in leaves of L. prostrata Roxb plants.


 Keywords: Ludwigia prostrata Roxb; Heavy metals; Near infrared reflectance spectroscopy; Near-infrared diffuse reflectance spectroscopy; NIDRS; Partial least squares; PLS.



Coupled Turbidity and Spectroscopy Problems: A Simple Algorithm for Volumetric Analysis of Optically Thin or Dilute 2-Phase Systems

 Paul W. Dent, Bin Deng, Jerry Goodisman, Joseph Chaiken


We report an algorithm for measuring the phase volume fraction and solute concentration of a two-phase system, applicable to either optically thin or optically dilute spatially homogeneous systems. Probing light is directed into the sample, and the elastically scattered light (EE) is collected as one signal and the inelastically scattered light (IE) collected as another signal. The IE can be pure fluorescence or Raman or an unresolved combination of the two. As the IE and the EE are produced by fundamentally different processes, they are independent. The algorithm, derived from radiation transfer theory, shows that phase volume and concentration are linear functions of the EE and IE. The parameters are derived from a training set. We present examples of how the algorithm performs when the assumption of spatial homogeneity is violated and when light-induced photochemistry causes changes in the IE. Although this is a generally valid algorithm with many potential applications, its use is discussed briefly in the context of blood and tissue analysis since the algorithm was originally designed for noninvasive in vivo probing of human skin.


Keywords: Turbidity corrected; Spectroscopic analysis; Fluorescence; Raman spectroscopy.



Transmission NIR and PTOF Spectroscopy in a Comparative Analysis of Pharmaceuticals

Faisal Kamran, Otto H. A. Abildgaard, Anders Sparén, Olof Svensson, Jonas Johansson, Stefan Andersson-Engels, Peter E. Andersen, Dmitry Khoptyar


We present a comprehensive study of the application of photon time-of-flight spectroscopy (PTOFS) in the wavelength range 1050–1350 nm as a spectroscopic technique for the evaluation of the chemical composition and structural properties of pharmaceutical tablets. PTOFS is compared to transmission near-infrared spectroscopy (NIRS). In contrast to transmission NIRS, PTOFS is capable of directly and independently determining the absorption and reduced scattering coefficients of the medium. Chemometric models were built on the evaluated absorption spectra for predicting tablet drug concentration. Results are compared to corresponding predictions built on transmission NIRS measurements.The predictive ability of PTOFS and transmission NIRS is comparable when models are based on uniformly distributed tablet sets. For non-uniform distribution of tablets based on particle sizes, the prediction ability of PTOFS is better than that of transmission NIRS. Analysis of reduced scattering spectra shows that PTOFS is able to characterize tablet microstructure and manufacturing process parameters. In contrast to the chemometric pseudovariables provided by transmission NIRS, PTOFS provides physically meaningful quantities such as scattering strength and slope of particle size. The ability of PTOFS to quantify the reduced scattering spectra, together with its robustness in predicting drug content, makes it suitable for such evaluations in the pharmaceutical industry.


Keywords: Spectroscopy; Scattering measurements; Turbid media; Multiple scattering; Spectroscopy, condensed matter.



Temperature Dependent Raman Spectroscopy of Melamine and Structural Analogs and Detection in Milk Powder

Walter F. Schmidt, C. Leigh Broadhurst, Jianwei Qin, Hoyoung Lee, Julie K. Nguyen, Kuanglin Chao, Cathleen P. Hapeman, Daniel R. Shelton, Moon S. Kim


Hyperspectral Raman imaging has the potential for rapid screening of solid-phase samples for potential adulterants. We can improve mixture analysis algorithms by defining a temperature range in which the contaminant spectrum changes dramatically and uniquely compared with unadulterated material. Raman spectra were acquired for urea, biuret, cyanuric acid, and melamine (pure and at 1% in dried milk powder) from 50 to 310 °C with a gradient of 1 °C min-1. Adulterants were clearly indentified in the milk powder. Specific frequencies that were mainly associated with ring breathing, stretching, and in-plane deformation shifted with respect to temperature up to 12 cm-1 in all four molecules. Specific frequencies significantly increased/decreased in intensity within narrow temperature ranges independent of whether the amine was mixed in milk. Correlation of Raman and differential scanning calorimetry data identified structural components and vibrational modes, which concur with or trigger phase transitions.

Keywords: Raman spectroscopy; Biuret; Cyanuric acid; Melamine; Hyperspectral imaging; Temperature-dependent Raman spectroscopy.



Spectroscopic Technique


Feasibility Study for Transforming Spectral and Instrumental Artifacts for Multivariate Calibration Maintenance

Joshua Ottaway, John H. Kalivas


Frequently, a spectral-based multivariate calibration model formed on a particular instrument (primary) needs to predict samples measured on other (secondary) instruments of the same spectral type. This situation is often referred to as calibration maintenance or transfer. A new calibration maintenance approach is developed in this paper using spectral differences between instruments. In conjunction with a sample-weighting scheme, spectral differences are piecewise (wavelength window) or full spectrum fitted with modeling terms (correction terms) such as polynomials and derivatives. Results demonstrating the potential usefulness of the new method using a near infrared (NIR) benchmark dataset are presented in this paper. The process does not need a standardization sample set measured in the primary condition. Thus, the new approach is a ‘‘hybrid’’ between the popular methods of extended inverted multiplicative signal correction (EISC) and direct standardization (DS) or piecewise DS (PDS). It is found that prediction errors reduce for samples measured in the secondary condition compared to those based on no calibration transfer. Prediction errors are also comparable to those from a full calibration in the secondary condition. In addition to instrument correction, an extension of the new approach is discussed (but not tested) for predicting new samples changing over time due to new chemical, physical, and environmental measurement conditions including individually or combinations of temperature, sample particle size, and new spectrally responding species.


Keywords: Calibration maintenance; Instrument transfer; Near infrared; NIR; Consensus modeling.









































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