Fourier transform raman spectroscopy using a bench-top fourier transform infrared spectrometer

The use of a bench top FTIR spectrometer for near infrared Fourier transform Raman spectroscopy is demonstrated. The use of near infrared excitation results in fluorescence free Raman spectra allowing previously difficult samples to be measured.     

Infrared photodissociation spectroscopy of electrosprayed ions in a Fourier transform mass spectrometer

Previous gas-phase methods for infrared photodissociation spectroscopy (IRPD) require sample volatility. Our method instead uses electrospray ionization to introduce even large nonvolatile molecules into a Fourier transform mass spectrometer, where extended (>15 s) ion storage makes possible high sensitivity spectral measurements with an OPO laser over a range of 3050-3800 cm(-1). The spectra of 22 gaseous proton-bound amino acid complexes are generally correlated with the H-stretching frequencies established for O-H and N-H functional groups in solution. For theoretical structure predictions of the Gly2H+ and N-acylated Asp2H+ dimers, IRPD spectra clearly differentiate between the predicted lowest energy conformers. In contrast to solution, in the gas phase the glycine zwitterion is approximately 20 kcal/mol less stable than the neutral; however, glycine is clearly zwitterionic in the gaseous GlyLysH+ dimer. The level of theory is inadequate for the larger Lys2H+ dimer, as all low energy predicted structures have free carboxyl O-H groups, in contrast to the IR spectrum. IRPD appears to be a promising new technique for providing unique information on a broad range of biomolecular and other gaseous ions, especially on noncovalent bonding involving O-H and N-H groups.     

Negative chemical ionization and accurate mass measurement applications for a linked gas chromatography/Fourier transform infrared spectrometer/Fourier transform mass spectrometer

Summary The analytical utility of a linked GC/FTIR/ FTMS system operating in accurate mass and negative CI modes is demonstrated. In addition to the complementary information derived from IR and MS search results, accurate mass measurement data (average error of 4.2 ppm) is employed in the analysis of a seven component mixture. A post search filter uses accurate mass data to eliminate spectral search results with incorrect elemental compositions. An alternate positive ion EI and negative ion CI GC/IR/MS analysis is also performed on a mixture of substituted phenyl aldehydes and ketones. The reagent gas, ammonia, is introduced by pulsed valve thus minimizing crossover spectral contamination while maximizing spectral resolution. Proton abstraction by the amide produces an intense (M-1)^– for all compounds in the mixture. Molecular weight information from the negative CI data is used in a post search filter to improve the reliability of both IR and MS search results.

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Anwendung der negativen chemischen Ionisation und genauer Massenmessungen für ein gekoppeltes GC/FTIR/FTMS-System

Zusammenfassung Die analytische Anwendbarkeit eines gekoppelten GC/FTIR/FTMS-Systems mit akkurater Massenmessung und NCI-Betrieb wird dargestellt. Zusätzlich zu den komplementären Informationen aus IR- und MS- Bibliothekssuchen werden Daten aus akkuraten Massenmessungen (mittlerer Fehler 4.2 ppm) bei der Analyse einer Mischung aus sieben Komponenten mit herangezogen. Im Anschluß an die Bibliothekssuche eliminiert ein Filter mit Hilfe der akkuraten Massen Ergebnisse mit fehlerhafter Elementarzusammensetzung. Von einer Mischung aus substituierten Phenylaldehyden und -ketonen wird eine Analyse mit alternierender Registrierung von positiven EI- und negativen CI-Spektren durch ein GC/IR/-MS-System ausgeführt. Das Reaktandgas Ammoniak wird über ein gepulstes Ventil zugegeben, um bei maximaler spektraler Auflösung minimale Störung durch Verunreinigung zu erhalten. Durch Abstraktion eines Protons von der Amidfunktion werden von allen Komponenten der Mischung intensive (M-1)-Ionen gebildet. Molekulargewichtsinformationen aus dem NCI-Experiment werden als Filter verwendet, mit dem die Zuverlässigkeit des Suchens in IR- und MS-Datenbanken erhöht werden kann.

     

Polarization modulation Fourier transform infrared spectroscopy

Polarization modulation Fourier transform infrared spectroscopy can be measured by either double modulation FTIR or interferometric modulation FTIR techniques. The principles of both techniques are presented with examples of representative measurements. The relative advantages and disadvantages of each method are compared.     

Dynamic Fourier transform infrared spectroscopy in polymer research

The rapid-scanning capability of FTIR instrumentation has revitalized the field of vibrational spectroscopy in polymer research and will be discussed with reference to the study of polyurethane kinetics, the temperature dependence of hydrogen bonding in polyamide 6 and strain-induced crystallization in a polydimethylsiloxane elastomer.     

Instrumental barriers in biological Fourier transform infrared spectroscopy

Biological applications of infrared spectroscopy have pressed for ever greater instrumental capabilities in terms of spectral sensitivity and quantitative exactness. Improved instrumentation has provided measurement of many vibrational modes in biological samples that previously were lost in noise. With highly optimized sampling conditions, useful measurements have been made with a peak-to-peak noise level less than 5 microabsorbance (5×10^–6 absorbance), at 0.5 cm^–1 resolution. However, optical and instrumental instabilities often result in sine waves that are not totally removed by the ratio of sample to reference. These often limit effective spectral sensitivity to 50 or 100 microabsorbance, peak-to-peak, and constitute a non-random noise. Non-atmospheric absorptions, especially one at 1959 cm^–1 with 0.8 cm^–1 band width (FWHM) are reported. The latter is due to a trace impurity in the KBr beam splitter substrate and compensator plate. Improvements in instrumentation and sampling conditions are expected to yield measurements of absorption bands as small as 50 microabsorbance with excellent signal/noise.     

Fourier transform infrared photoacoustic spectroscopy of dental calculus

The mid and far FTIR spectra of supragingival and subgingival calculus were measured, respectively. From the subtraction spectra of the two types of calculus, the protein components of calculus have been obtained. The results of photoacoustic spectroscopy indicated the presence of protein layer on the surface of early calculus.     

MICRA: a compact permanent magnet Fourier transform ion cyclotron resonance mass spectrometer

MICRA, a compact Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometer is described. The amount of miniaturisation in this device, based on a 1.24 T permanent magnet, remains compatible with genuine FT-ICR performance and analytical power in the mass range 2-1000 m/z, with a mass resolving power of 73,000 at mass 132. A first application of the transportability is the repetitive coupling of MICRA with a large-scale source of IR photons, the free electron laser CLIO.     

Wide mass range trapping using a 7-T internal source matrix-assisted laser desorption/ionization Fourier transform mass spectrometer

A wide mass range trapping experiment using internal source matrix-assisted laser desorption–Fourier transform mass spectrometry (MALDI–FTMS) was evaluated. In this method, the front trap plate potential is ramped up and the rear trap plate potential is simultaneously decreased using a cubic cell to trap ions over a wide range of mass-to-charge ratios. To apply this to MS/MS experiments, a second ion ejection procedure would remove unwanted ions, with the selected remaining ions then fragmented by collision-induced dissociation. In measurements using a 7.2-T unshielded magnet presented here, an approximately equimolar mixture of a set of poly(ethylene glycol) (PEG) species for the ramped measurements had peak areas of 1.0:1.0:1.0:1.0, as did the previously described integral method which gave peak areas of 1.0:1.1:1.0:1.0, in good agreement with the known composition of the samples deposited on the MALDI probe tip. Comparative MALDI–TOF in reflectron mode results were of similar quality for the equimolar mixture, giving a ratio of 1.0:1.0:1.2:0.9. All methods failed to varying degrees when individual PEG compositions of the trial mixture were changed. However, the previously described integral method showed relatively better results for all but the PEG 8000 doubled mixture.     

In situ Fourier transform infrared spectroscopy as an efficient tool for determination of reaction kinetics

The performance of new FTIR-based monitoring technology to representatively determine reaction kinetics has been demonstrated on an example of homogeneously catalyzed liquid-phase sucrose hydrolysis to fructose and glucose. The reaction kinetics were investigated by using the ReactIR 1000 reaction analysis system, which enables determination of the component concentration from its characteristic FTIR spectrum. During the sucrose inversion, the ReactIR 1000 instrument connected to a computer controlled standard glass batch reactor provided the required operating conditions and information about the component concentration in real-time. We have studied the influence of hydrogen ion concentration, temperature and initial concentration of sucrose on the sucrose disappearance rate. It was found out that the inversion of sucrose is an irreversible reaction, which is not affected by the formation of fructose and glucose in the liquid-phase. Then, the parameters of the kinetic model (i.e., reaction rate constant and activation energy) were calculated. A comparison of the model output and the measured data showed that the kinetics of the sucrose inversion could be well described by means of the pseudo first-order kinetic model. Finally, the method of determining the kinetic model by FTIR spectroscopy was verified by comparing the results obtained in the batch reactor with the results obtained in the continuously stirred tank reactor.     

Fourier transform infrared spectroscopy study of nanostructured nickel oxide

Nanostructured nickel oxide having different average particle sizes ranging from 3 to 16 nm were synthesized and Fourier transform infrared (FTIR) spectra of the samples were recorded in the far infrared (IR) region. The spectra were found to be dominated by surface mode absorptions with no distinct absorption corresponding to the bulk transverse optical mode. IR absorption coefficient, alpha, for the nanostructured NiO samples were calculated as a function of frequency using a macroscopic approach devised by Fuchs. The effects of crystalline geometry, numerical values of optical constants, filling factor and increased damping on the spectral features of the samples were analyzed. Though the simulations approximately reproduced the occurrence of a shoulder in the experimental spectra, the most intense peak in the simulated spectra was found to be about 50 cm(-1) above the corresponding experimentally observed peak. It was shown that the experimentally observed absorption maximum of all the samples were in close agreement with that determined using a microscopic theory based on the rigid ion model. The weak absorption peaks in the frequency region 60-100 cm(-1) appearing in the spectra of all the samples were identified as surface induced transverse acoustical modes, omegaTA, which became IR active due to the breakdown of translational symmetry in the nanocrystallites.     

Sexing of turkey poults by Fourier transform infrared spectroscopy

Fourier transform infrared (FT-IR) spectroscopy was used to probe the molecular composition of germinal cells and to identify the gender of turkey poults. Germinal cells obtained from a feather pulp were characterized by FT-IR micro spectroscopy. The sample set consisted of growing contour feathers from 23 male and 23 female turkey poults. Significant spectral variations were observed in the range between 1,000 and 1,250 cm⁻¹. The spectra of male turkey poults exhibit a significantly higher content of RNA than those of female turkeys. Spectral classification was performed by a non-supervised method based on the principal component analysis. An evaluation of the first and third PCs led to a classification of female and male poults with an accuracy of more than 95%.     

PH-dependent coordination of metal-lisinopril complex investigated by attenuated total reflection/Fourier transform infrared spectroscopy

In order to simulate the in vivo binding behavior of angiotensin-converting enzyme (ACE) inhibitors to the zinc-containing active center of ACE, the in vitro interaction between lisinopril and zinc or nickel ions was investigated in aqueous solutions of different pH by using attenuated total reflection (ATR)/Fourier transform infrared (FT-IR) spectroscopy with second-derivative IR spectral analysis. The results indicated that the lisinopril dissociation process occurred in a stepwise fashion during increase in pH. The IR peaks at 1642 cm(-1) (carbonyl stretching of tertiary amide) and at 1582 cm(-1) (asymmetric COO- stretching) for lisinopril in solution at pH 3.5 shifted to 1606 and 1586 cm(-1) after addition of Ni2+ ions, respectively, but there was no marked changes in IR spectra of lisinopril after addition of Zn2+ ions. When the Zn2+ ions were added to lisinopril solution at pH 5.0, the peak at 1642 cm(-1) also shifted to 1604 cm(-1) and the peak at 1582 cm(-1) shifted to 1586 cm(-1), similar to the changes at pH 3.5 after adding Ni2+ ions. However, the peaks at 1582 and 1642 cm(-1) both shifted to 1599 cm(-1) after addition of Ni2+ ions at pH 5.0 or at pH 7.3. The peak at 1576 cm(-1) also shifted to 1599 cm(-1) after addition of Zn2+ ions to lisinopril solution at pH 7.3. Different coordination sites or types (chelating, bridging or pseudounidentate complex) between lisinopril and Zn2+ or Ni2+ ions were proposed, based on the separation value between v(as) (COO-) and v(s) (COO-), and the shifting of carbonyl groups. Coordination of the secondary amine in lisinopril to metal ions was also evidenced.     

Pressure-dependent Fourier transform infrared spectroscopy of a poly (ester urethane)

The effects of hydrostatic pressure upon (1) a segmented poly (ester urethane), (2) a hydrolytically degraded sample of the same polymer, and (3) models for the polyurethane and polyester segments in this polymer have been studied by Fourier transform infrared spectroscopy using high-pressure diamond anvil cells (DACs). The pressure responses of the vibrational frequencies of specific functional groups of the poly (ester urethane) in the 0-100-kbar range are compared with data for individual segment models and the partially degraded sample. The results indicated that the polymer is highly stable in this pressure regime, with no measurable degradation or phase changes. Differences in the pressure dependency of specific infrared bands between the poly (ester urethane) sample and the partially degraded sample are slight and consistent with changes in hydrogen-bonding interactions and shorter chain lengths in the degraded sample.     

Time-resolved Fourier transform infrared emission spectroscopy of laser ablation products

Time-resolved Fourier transform infrared spectroscopy was applied for observations of emission spectra from ablation products induced by a Nd:YLF laser with a 2.5 kHz repletion rate. The infrared emission spectra from Fe, Cu, Zn, and Al atoms were observed in the 2.5–5 μm region. The observed emission spectrum from iron ablation in the 2500 cm⁻¹ region agrees very well with solar absorption spectrum, where new lines have been detected in the present experiment in addition to the lines observed from a hollow cathode discharge. When O₂ was added to the carbon ablation, emissions from vibrationally excited CO were observed with non-equilibrium vibrational distribution.     

Preparation of dimethoxyborane and analysis by Fourier transform infrared spectroscopy

Dimethoxyborane was prepared by the reaction of trimethoxyboroxine, sodium borohydride and trimethyl borate in diethylene glycol dimethyl ether solvent at 70°C under atmospheric pressure followed by distillation to increase the purity and analyzed in liquid phase by FT-IR. The concentration of dimethoxyborane was identified by hydrolysis with water, which yields boric acid, methanol and hydrogen, whereas the generated hydrogen was analyzed by the mass detector of a volumetric flow apparatus. The FT-IR absorbance peak area showed a linear dependence on dimethoxyborane concentration in the wavenumber range 873 to 950 cm⁻¹ for samples with dimethoxyborane concentrations 0 to 6.2 wt% in trimethyl borate. Data fitting using the least square method gave an R ² value of 97%.     

Detection of weathering in stockpiled coals by Fourier transform infrared spectroscopy

The process of natural oxidation of two low-rank coals exposed to the atmosphere for 11 months has been studied by Fourier transform infrared (FT-IR) spectroscopy. The study was carried out on samples taken at different time intervals and additionally from zones where signs of high oxidation and self-ignition were detected. The aliphatic hydrogen (3000-2800 cm⁻¹) and oxygen-containing structures (1800-1500 cm⁻¹) regions of the spectra were examined by curve-fitting analysis and a series of structural parameters based on ratios of integrated absorbance areas of curve-fitted bands were established. The aliphatic hydrogen content of samples tended to decrease with increasing time of storage and carboxyl groups only increased slightly under conditions of low pile activity. When oxidation and self-ignition processes took place, the structural changes were more significant. Aliphatic structures decreased drastically and net production of oxygen-containing structures was observed. Aliphatic hydrogen content evaluated from integrated absorbance measurements of normalized spectra and the CO/aliphatic hydrogen ratio seemed to be very sensitive in detecting signs of weathering even at very low levels of activity.     

A comparison of Fourier transform infrared and near-infrared Fourier transform Raman spectroscopy for quantitative measurements: An application in polymorphism

Polymorphism in cortisone acetate, a synthetic adrenocortical steroid, and in a compound from a heart disease project has been studied with near-infrared Fourier transform Raman (NIR FT-Raman) spectroscopy. For cortisone acetate similar quantitative precision was obtained with both Raman and diffuse reflection IR measurements. The Raman measurements of the heart disease compound gave a calibration with a standard error of prediction of better than 2.5%. The combination of excellent precision with very convenient measurement of powders makes NIR FT-Raman spectroscopy a valuable tool for quantitative measurements of polymorphism.     

A Fourier transform time-of-flight mass spectrometer. A SIMION calculation approach

A new kind of approach to time-of-flight type spectrometers is presented on the basis of SIMION calculations. The detector studied is a short cylindrical tube capacitor closed with parallel plates at both ends. The main principle of operation is to force ions of equal energy to circulate in the volume between the two tubes on a path of equal radius and measure their flight times pro revolution which corresponds to the frequency of oscillation. By performing spectral analysis on the received signal through transformation from the time domain to frequency space the different masses can be detected.To study the expected performance of the FT-TOF detector, calculations of ion trajectories have been made by varying the dimensions and electric potentials of the electrodes. The effect of the beam position, variations in the angle of entrance and ion energy to the trajectories was calculated to monitor the resolution that is achievable.