INAA of cortical and trabecular bone samples from animals

Instrumental neutron activation analysis (INAA) was applied to determine Ba, Br, Ca, Cl, Fe, K, Mg, Mn, Na, P, Sr and Zn in bovine and porcine rib bones. Precise results were obtained in analyses of freeze-dried cortical and trabecular bones separately, and also of whole bone ashes. Cortical tissues presented higher concentrations of Ba, Ca, Mg, Mn, Na, P, Sr and Zn than those obtained in trabecular ones. Comparisons were also made between the results obtained for bovine and porcine rib bones. This revised version was published online in August 2006 with corrections to the Cover Date.     

Exploratory data analysis of infrared spectra

Summary Different linear mapping methods have been applied to sets of middle infrared spectra. Partial-least-squares (PLS)-substructure-mapping is shown to be an efficient, alternative method to the well-known principal component and linear discriminant techniques. Combination of chemical substructure analysis of object clusters in the projection plane and loading interpretation to detect significant spectral features can reveal spectrum-structure-relationships.     

Storage, retrieval and analysis of infrared spectra

Summary A system for computer-aided storage, retrieval and analysis of fully digitized IR spectra is presented. The on-line spectra acquisition and the procedures of data reduction are described. The additional storage of the chemical structure and the corresponding substructure codes allows a direct evaluation of structural features on the basis of the identity of spectral behaviour. The analysis of the substructure codes is used to optimize the parameters of the matching factor. In several examples the applications of the system with respect to identification, structure and substructure elucidation as well as the different output possibilities are demonstrated.

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Speicherung, Wiederauffindung und Analyse von Infrarotspektren

Zusammenfassung Ein rechnerunterstütztes IR-Spektren-Suchsystem mit vollständig digitalisierten IR-Spektren wird vorgestellt. Die on-line Datenerfassung, die Übertragung der Spektren zum Großrechner und die verschiedenen Möglichkeiten der Datenreduktion für die weitere Verarbeitung werden beschrieben. Die zusätzliche Speicherung der chemischen Struktur sowie der entsprechenden Teilstrukturcodierungen ermöglicht eine direkte Ermittlung von strukturellen Eigenschaften aufgrund spektroskopischer Übereinstimmung. Die Auswertung der Häufigkeit der relevanten Teilstrukturen im Anschluß an einen Spektrensuchlauf mit bekannten Substanzen wird zur Optimierung der Parameter des Vergleichsfaktors benutzt. In verschiedenen Beispielen werden die Ergebnisse bei der Spektrenidentifizierung, der Struktur- und der Teilstrukturermittlung sowie die verschiedenen Möglichkeiten bei der Darstellung der Suchergebnisse aufgezeigt.

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Dedicated to Prof. Dr. Otto Westphal on occasion of his 70th birthday     

Principal component analysis of the infrared spectra of mixtures

Principal component analysis of the infrared spectra of a series of related mixtures is used to determine the number of compounds present. The use of empirical error estimates makes it possible to determine correctly the number of components even when the spectra of the individual compounds are very similar.     

Target factor analysis of infrared spectra of multicomponent mixtures

The target factor analysis (t.f.a.) error criteria discussed earlier are applied to Fourier-transform infrared spectra in order to determine, without any prior knowledge of the experimental error, the number and identities of components in a series of related multicomponent mixtures. The t.f.a. method is also used for quantitative analysis and is compared to regression analysis, which force-fits the data and does not compensate for an impurity of small but measurable quantity. In addition, it is shown how an impurity in a single mixture can be detected, identified, and quantified. An actual experimental example is presented, using solutions of o-xylene, m-xylene, p-xylene, and ethylbenzene in cyclohexane, with chloroform as an impurity.     

Structural analysis and Fourier transform infrared and Raman spectra of dibutoxyphosphoryl benzylisothiourea

A structural analysis for dibutoxyphosphoryl benzylisothiourea (DBBT) was carried out by mass spectrometry, 1H NMR, 13C NMR, infrared and Raman spectroscopy. The Fourier transform infrared and Fourier transform Raman spectra of liquid of DBBT were carried out with the purpose of studying the tautomerism (structures I and II) and the behavior of the more polar absorption's bands in different solvents, i.e., absorption's of the P=O and C=N bands. The results suggest the existence of tautomerism in the pure (liquid) compound and in solution of CHCl(3), CH(2)Cl(2), CHBr(3), and THF, C(2)H(4)Cl(2) and C(2)H(4)Br(2). The solvent interaction with the P=O band was characterized by the presence of a new band in the region of the O-H absorption. A vibrational assignment of the IR bands and Raman shifts was done and is proposed in this paper.     

The infrared spectra and normal coordinate analysis of syn and anti acetaldoxime

The infrared spectra of mixtures of syn and anti acetaldoxime and its deuterated analogues CH₃CHNOD, CD₃CHNOH, CD₃CDNOH and CH₃CDNOH have been recorded. The syn and anti isomers of CH₃CHNOH, CD₃CHNOH, CD₃CDNOH and CH₃CDNOH have been separated by gas chromatography [1]. The infrared spectra of separated isomers in CS₂ solution have been recorded and the assignment of ten in-plane vibrations made. From a normal coordinate analysis the Urey-Bradley force field, the potential energy distribution and additional information about assignments have been obtained.For the anti isomer the simple Urey-Bradley force field gives satisfactory agreement between the calculated and measured frequencies. For the syn isomer it is necessary to take into account the interactions between atoms separated by three bonds.     

The wavelet transforms and statistical models for near infrared spectra analysis

Often extensive spectral data is collected on multiple samples with the goal of predicting one or more properties of the sample. For example, measurements can be made at hundreds of wavelengths along with the more expensive assay values. The predictor variables are often highly correlated and it is expected that only small sections of the wave are pertinent to the measured analytes. There is a need to simplify or compress the predictors to both save data storage and possibly de-noise the data prior to making predictive models. Our idea is to use a factorial design (a two-step frame work) to explore two wavelet transformations, Haar wavelets and Daubechies wavelets, with progressively better approximation to the raw data curves in combination with several statistical prediction methods, including stepwise regression, principal component regression, ridge regression and partial least squares regression. The plan is to study prediction quality using Haar-Step, Haar-PCR, Haar-PLS, Haar-Ridge, Daubechies-Step, Daubechies-PCR, Daubechies-PLS and Daubechies-Ridge. Often PLS and stepwise regression can predict substance concentrations equally well. In such situations, the preferred statistical method should be the simplest method. From our studies, we conclude that the type of wavelet is unimportant, the number of wavelets should be large enough to capture most of the variability in the wave forms, and the choice of the statistical method depends on the analyte.     

Application of neutron activation analysis to bone samples

Summary Neutron activation analysis technique, using Au as flux monitor, was applied to determine element concentrations of Ca, K, Na, Mg, Mn and Sr in certified reference material (NIST 1400 Bone Ash). The results were compared with those using comparative INAA and they were compatible. The same results were obtained using the recommended k₀ factors, in order to obtain the activation cross section as input in concentration for the same reference material. Some applications in the health area aiming clinical evaluation in bone samples of medium and small-sized animals were performed and the viability of using this methodology was discussed.     

Computer-assisted interpretation of infrared spectra

Pattern recognition and artificial intelligence programming techniques for the interpretation of infrared spectra are compared in an effort to determine the best technique for assisting the solution of actual structural elucidation problems. For several reasons, artificial intelligence is the method of choice. When information pertaining to a large number of classes is required, an excessively large training set would be needed with pattern recognition procedures. If the program makes a mistake, it must be alterable so that a similar error will not occur again. Artificial intelligence programs are amenable to this correction procedure.     

Frequency self deconvolution in the quantitative analysis of near infrared spectra

In this paper a new model based on frequency self deconvolution (FSD) is proposed for the quantitative analysis of a near infrared (NIR) spectrum. The model couples FSD and partial least square regression (PLS). The grid search optimization method is used to select the optimal values of the full width at half height (FWHH) and the truncation point of the apodization function. The proposed FSD-PLS provides a significant improvement in the prediction ability of the PLS model. Furthermore, a modification of the new FSD-PLS method is introduced to enable the removal of the baseline variations from the NIR spectra. The proposed models were validated using absorbance spectra of mixtures composed from glucose, urea and triacetin in a phosphate buffer solution where the concentrations of the components are selected to be within their physiological range in blood. The whole experiments were carried out in a non-controlled environment to show that the model can suppress effectively most of the experimental variations. The results show that the standard error of prediction (SEP) decreases from 35.58 mg dL(-1) using 8 factors for the PLS model to 15.53 mg dL(-1) by using 12 factors for the modified FSD-PLS model. The proposed models are also shown to yield a slightly improved performance than a newly developed second derivative-PLS model without incurring the shortcoming associated with the derivative approach in not providing interpretable results and in degrading the SNR of the spectra at a faster rate.     

Far infrared spectra of hexachalcogenohypodiphosphates

The far infrared (fir) reflection spectra of the hexachalcogenohypodiphosphates M₂P₂X₆ (M = Mg, Cd, Mn, Fe, Co, Ni, Pb, Sn; X = S, Se) have been studied. $\text{TO}\text{LO}$ splittings are determined from Kramers-Kronig analyses, the splitting is large for the lattice vibration modes of ferroelectric Sn₂P₂S₆ but very small for Ni₂P₂S₆. Measurements with polarized light permit an assignment of the A_2u and E_u modes of the ethane like P₂S₆ units in Mn₂P₂S₆. Factor group analyses were performed for all hitherto described hexachalcogenohypodiphosphates. The fir absorption spectra of the less symmetric compounds Hg₂P₂S₆, Hg₂P₂Se₆, Ca₂P₂S₆, TiP₂S₆, $\text{In}{}_{\mathrm{<mtext>4</mtext><mtext>3</mtext>}}\text{P}{}_2\text{S}{}_6\text{, In}{}_{\mathrm{<mtext>4</mtext><mtext>3</mtext>}}\text{P}{}_2\text{Se}{}_6$, and CuCrP₂S₆ are given.     

Hierarchical clustering of infrared spectra

The generation of a hierarchical tree of 500 infrared spectra, using the recently proposed fractal or 3-distances-clustering method is described and discussed. The objects of clustering are infrared spectra of polymer compounds which are represented as sets of 80 complex Fourier coefficients, obtained by fast Fourier transformation of digitized absorbance spectra. The generated hierarchical tree, with a maximum height of 20 and an average height of 12 levels, yields a very satisfactory clustering scheme with respect to the structure of the compounds involved. In addition to very good clustering, a 100% retrieval (prediction) ability was obtained. This was achieved by the use of an iterative procedure after the initial tree had been generated. Additionally, the tree was tested with 240 infrared spectra of different compounds which were taken into account during the generation of the tree. The retrieval success of these test runs is discussed with respect to the structural similarity of the compounds to which the “unknown” spectra were linked.     

Attenuated total reflectance powder cell for infrared analysis of hygroscopic samples

An attenuated total reflectance (ATR) sample cell has been designed, manufactured and subsequently used for the mid-infrared analysis of hygroscopic samples. This sample cell was installed as a simple drop-in replacement for the cell supplied with our commercially available Harrick Mvp-Pro FTIR–ATR accessory. Calcium chloride, a well-known desiccant that has a propensity to absorb water into its crystal lattice, was selected as non-infrared active substrate to accentuate the efficacy of the cell in preserving the anhydrous state of the sample by straightforward monitoring of the water bands. In contrast, mid-infrared spectra are presented that qualitatively demonstrate the rapid rate at which atmospheric moisture is incorporated into the anhydrous sample when analyzed using the conventional ATR cell assembly.     

Far infrared spectra,vibrational assignment and normal coordinate analysis of the tricyanomethanideion

Far infrared spectra of the tricyanomethanide ion C(CN)₃^? in solution and in the solid state have been investigated. The results allow a complete vibrational assignment to be made. A normal coordinate analysis has been carried out, the results of which are compatible with the existence of some double bond character in the C-C bonds of C(CN)₃^?.     

Raman and infrared spectra of crystalline fluoroform

Raman and far-infrared spectra of crystalline fluoroform at temperatures between 20 and 106 K have been recorded. There is no evidence for any solid-state phase transitions, nor for hydrogen bonding. The rich lattice spectra and crystal field splittings suggest that the unit cell is rather large, and possible structures are discussed.     

Raman and infrared spectra of crystalline chloroform

Raman and far-infrared spectra of polycrystalline samples of chloroform at 20 and 80 K are reported. Crystal field spilttings of the intramolecular fundamentals are observed as well as nine Raman and six infrared lattice modes. Spectra are interpreted in terms of a group theoretical analysis based on the molecular and crystal symmetries.