Applied Spectroscopy

Arvanitopoulos, Constantinos D.; Koenig, Jack L.

doi: 10.1366/0003702963906717pmid: N/A

Glass fiber-epoxy with composites were analyzed with the use of FT-IR microspectroscopy. With the use of spectral subtraction along with two-dimensional mapping experiments, spectral features characteristic of the interfacial region were revealed. Different types of glass fibers were used in order to observe spectral differences at the interphase. When as-received and heat-cleaned glass fibers were used, certain similarities were observed, although an inhibition of the curing seems to be taking place at the interfacial region of epoxy-heat-cleaned glass fibers. When the glass fibers were treated with an aminosilane coupling agent (γ-APS), there was spectral evidence that the glass surface was modifying the epoxy-glass fiber interphase.

Arvanitopoulos, Constantinos D.; Koenig, Jack L.

doi: 10.1366/0003702963906735pmid: N/A

Infrared imaging was utilized to analyze the behavior of epoxy-glass fiber composites when exposed to moist conditions. With the use of mapping subtraction, the differences in the water uptake were revealed when different types of glass fibers were used. Composites prepared with as-received glass fibers exhibit the highest water uptake at the interphase as opposed to those prepared with silane-treated glass fibers, which exhibit the lowest uptake. Moreover, the epoxide deformation band was examined in order to analyze the effect of water on the curing of the composites. Water was found to catalyze a polymerization reaction at the interphase, but only if a certain level of water concentration is present is the above phenomenon detectable.

Fletcher, T. Rick; Rekow, Matt; Rogge, Dwayne; Sammeth, David

doi: 10.1366/0003702963906799pmid: N/A

A technique is described which uses a laser-generated high-velocity polymer flyer to vaporize nonvolatile molecules and low-temperature matrix-isolated species. Morphology studies, time-of-flight measurements, static collection methods, and real-time laser-induced fluorescence were used to characterize the new vaporization technique. Cr(CO)6 in a mineral oil glass at 77 K, rhodamine dye, and naphthalene were vaporized in these experiments.

Mank, A. J. G.; de Nijs, H.; Lingeman, H.; Brinkman, U. A. Th.; Velthorst, N. H.; Gooijer, C.

doi: 10.1366/0003702963906681pmid: N/A

A diode laser-based absorption detector is designed for conventional-size liquid chromatography (LC). To this end, various detection setups and individual components have been evaluated. A ratioing system using a 10-mW 670-nm diode laser allowed the detection of 6 × 10−10 M mitoxantrone [signal-to-noise (S/N) = 3; N = root-mean-square (rms) noise], an anti-tumor drug, in a biological matrix without any sample cleanup. Multipass detection and intensity modulation of the excitation light did not improve the detection limit. A fiber-optic detector cell, utilizing a gradient-index lens on the light-guiding fiber, was a good and robust alternative for the standard absorption detector cell. Detection limits with the use of the diode laser-based detector are 20-fold better than those obtained with a commercial absorption detector for LC.

Wabuyele, Busolo Wa; Harrington, Peter De B.

doi: 10.1366/0003702963906708pmid: N/A

A fuzzy optimal associative memory (FOAM) has been devised for background correction of near-infrared spectra. The FOAM yields improved predicted background scans for calculation of near-IR absorbance spectra of glucose in plasma matrices from single-beam data. The FOAM is an enhanced optimal associative memory (OAM) that uses a fuzzy function for encoding the spectra. The FOAM can predict a matching reference spectrum for a near-IR absorbance spectrum with low glucose absorbances by using second-derivative spectra. Glucose concentrations were predicted from calibration models furnished by partial least-squares (PLS). The FOAM stored reference spectra obtained from either water/phosphate buffer or plasma/glucose solutions. Both of these associative memories were evaluated. The standard error of prediction (SEP) for glucose concentration from an optimal PLS calibration model based on FOAM-corrected spectra was 0.60 mM for the water/phosphate buffer spectra. For FOAM-corrected spectra from plasma/glucose reference spectra, the SEP was 0.68 mM. The SEP of conventionally corrected double-beam second-derivative spectra was 0.81 mM. FOAM-corrected spectra generally furnish improved calibration models.

Craggs, C.; Galloway, K. P.; Gardiner, D. J.

doi: 10.1366/0003702963906636pmid: N/A

One- and two-channel maximum entropy methods (MEMs) have been applied to simulated and experimental Raman spectra of both single and double (overlapping) bands. The extent to which signal recovery is affected by signal-to-noise ratios has been determined with the use of measures based on the mean sum of squared residuals, loss of band intensity, and band area reduction. The analysis demonstrates that the two-channel approach results in improved signal recovery, especially at high signal-to-noise ratios.

Fang, Ye; Bai, Chunli; Wei, Ying; Tang, Youqi

doi: 10.1366/0003702963906780pmid: N/A

In this research, we studied the adsorption structure of an RNA triplex, poly[rU]poly[rA]poly[rU], at a silver electrode by surface-enhanced Fourier transform Raman scattering (FT-SERS) spectroscopy and compared it to those of the corresponding single-stranded poly[rA] and duplex poly[rA] · poly[rU]. Some interesting phenomena have been observed. At the ex situ electrochemically roughened silver electrode, the SERS behavior of the duplex RNA is close to that of the single-stranded poly[rA], thereby indicating that the duplex RNA adsorbed at the electrode might be partly destabilized. However, on the highly positively charged surfaces, the SERS spectra revealed that the triplex was predominantly adsorbed at the electrode via the phosphate-moiety-directed mechanism, and thus the helical structure of the triplex molecules was well preserved; furthermore, since the electrode potential was set to approach the potential of zero charge (pzc) of the silver metal, in the spectral region between 1800 and 600 cm−1 the triplex gives rise to SERS spectra similar to those of the corresponding duplex, and also yields only two enhanced signals at 734 and 1382 cm−1, due to the ring-breathing and ring-vibration modes of the adsorbed adenine residues, respectively, along with the disappearance of some bands originating from the corresponding rU residues and phosphate groups. In fact, a dramatic transition of the SERS spectra of the triplex at the electrode was found to occur between −0.2 and −0.4 V. On the basis of the structural characteristics of triple-helical nucleic acids, we concluded that in this case there are two types of competitive adsorbed species—the triplex itself and the unpaired adenine residues in the incomplete region of the triplex RNA—which might be responsible for the unique potential-dependent transition.

Wang, Jiangshan; Hurtubise, Robert J.

doi: 10.1366/0003702963906753pmid: N/A

A new kind of solid matrix, glasses from sugars, was developed for trace organic analysis. Clear glasses of glucose and trehalose were prepared by evaporating the sugar solutions onto solid supports. It was determined that the ratio of methanol to water was very important in forming a clear glass. Also, glasses made from pure trehalose often cracked. However, with the addition of 8–10% NaCl to the trehalose, no cracks were formed. Clear and rigid glasses of both glucose and trehalose/NaCl were obtained on quartz plates. Strong room-temperature fluorescence (RTF) and room-temperature phosphorescence (RTP) were obtained from benzo[f]quinoline (B[f]Q), 4-phenylphenol (4-PP), (tetrol I-1), triphenylene, and phenanthrene. The limits of detection (LODs) of both the RTF and RTP for 4-PP and B[f]Q in the glasses were in the subnanogram milligram range.

Griffith, David W. T.

doi: 10.1366/0003702963906627pmid: N/A

A method for the quantitative analysis of gas-phase infrared spectra is described in which calibration spectra are calculated from a database of absorption line parameters rather than measured in a real spectrometer. The synthetic calibration spectra are computed with the use of the program MALT (Multiple Atmospheric Layer Transmission), including environmental (pressure, temperature, pathlength, etc.) and instrumental (resolution, line shape, wavenumber shift) effects in the calculation, so that the calculated spectra closely approximate real measured spectra. The synthetic calibration spectra are then used in quantitative analysis as if they were real spectra. In conventional laboratory studies, the method circumvents the need for time-consuming collection of large sets of laboratory calibration spectra often required when many absorbing gases must be analyzed. It is particularly useful in long open-path and solar FT-IR spectroscopy when no sample cell is available for recording calibration spectra. Examples are presented from conventional laboratory spectra in a closed-cell, open-path FT-IR spectra used to determine trace gas fluxes in an open field, and solar absorption spectroscopy using ground-based FT-IR spectrometers.

Aardahl, Christopher L.; Davis, E. James

doi: 10.1366/0003702963906663pmid: N/A

The hydrolysis of a solid NaOH microparticle in humid nitrogen and the chemical reaction between the resulting NaOH solution microdroplet and SO2 gas have been studied with the use of elastic and inelastic (Raman) light scattering. A single solid NaOH particle was levitated electrodynamically in a reaction chamber and exposed to water vapor. After hydrolysis/deliquescence, the resulting solution droplet was exposed to SO2 gas. Raman spectra and elastic resonance spectra collected during the reactions indicate that low SO2 concentrations in the gas phase yield NaHSO3 while high SO2 concentrations result in Na2SO3 as the product. These results indicate that the reversibility of the key reactions becomes important when the SO2 concentration is low.