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Showing papers in "Applied Spectroscopy in 1998"


Journal ArticleDOI
TL;DR: In this article, the effect of colloidal gold clusters on surface-enhanced Raman scattering (SERS) enhancement has been investigated and it was shown that colloidal clusters can provide an enhancement level sufficient for Raman single molecule detection.
Abstract: In agreement with previous results reported for colloidal silver clusters, effective surface-enhanced Raman cross sections of about 10-16 cm2 per molecule, corresponding to enhancement factors on the order of 10 14, have also been obtained for molecules attached to colloidal gold clusters. Spatially isolated nearly spherical colloidal gold particles of about 60 nm size show maximum enhancement factors on the order of 103 at 514 nm excitation, close to the single plasmon resonance. The enhancement factor increases by eleven orders of magnitude when colloidal gold clusters are formed by aggregation of the gold colloids and when near-infrared excitation is applied. The large effective surface-enhanced Raman cross section has been estimated by a straightforward method based on steady-state population redistribution due to the pumping of molecules to the first excited vibrational state via the strongly enhanced Raman process. Our experimental finding confirms the important role of colloidal clusters for extremely large surface-enhanced Raman scattering (SERS) enhancement factors. Simultaneously, it suggests colloidal gold clusters as a substrate for high-sensitivity surface-enhanced Raman scattering, which can provide an enhancement level sufficient for Raman single molecule detection. Due to its chemical inactivity, gold might have some advantages compared to silver, particularly in biomedical spectroscopy.

260 citations


Journal ArticleDOI
TL;DR: In this article, laser-induced breakdown spectroscopy has been applied to polymer samples in order to investigate the possibility of using this method for the identification of different materials, such as polyethylene (HDPE), polyvinyl chloride (PVC) and polypropylene (PP).
Abstract: Laser-induced breakdown spectroscopy has been applied to polymer samples in order to investigate the possibility of using this method for the identification of different materials. The plasma emission spectra of high-density polyethylene (HDPE), low-density polyethylene (LDPE), polyvinyl chloride (PVC), polyethylene terephthalate (PET), and polypropylene (PP) have been studied. Spectral features have been measured-for example, the 725.7 nm chlorine line, the 486.13 mm H-beta line, and the 247.86 nm carbon line whose evaluation with neural networks permits identification accuracies between 90 and 100% , depending on polymer type.

197 citations


Journal ArticleDOI
TL;DR: In this paper, a method for generating the wavelength-dependent correction file by using six secondary emission standards based on commercially available fluorophors is presented. But the method is not suitable for the measurement of the entire wavelength range and significantly worse over the wavelength region of a typical spectrum.
Abstract: Technical spectra are reported for a series of six secondary emission standards based on the commercially available fluorophors: tryptophan, alpha-NPO, tetraphenylbutadiene, coumarin 153, DCM, and LDS 751. These spectra cover the wavelength range between 300 and 800 nm with significant spectral overlap and conform to the requirements of secondary emission standards. Standard emission spectra are determined by averaging the technical spectra obtained from three independently calibrated fluorescence spectrometers. A method for generating the wavelength-dependent correction file by using these standards is outlined. Comparison to the National Bureau of Standards (NBS)-reported quinine sulfate spectrum illustrates the accuracy of both the emission standards and the method of generating a complete emission correction file. With the use of the standards and method reported here, the accuracy of the emission correction is estimated to be better than 10% for the entire wavelength range and significantly better over the wavelength region of a typical spectrum.

184 citations


Journal ArticleDOI
TL;DR: In this paper, a single-molecule Raman spectroscopy of a cyanine dye in aqueous silver colloidal solution with the use of surface-enhanced Raman scattering at near-infrared excitation (NIR-SERS) is reported.
Abstract: Single-molecule Raman spectroscopy of a cyanine dye in aqueous silver colloidal solution with the use of surface-enhanced Raman scattering at near-infrared excitation (NIR-SERS) is reported. A characteristic Poisson distribution of SERS signals due to the Brownian motion of single dye molecule-loaded silver particles reflects the probability of finding 0, 1, or 2 1,1 ' -diethyl-2,2 ' cyanine (PIC) molecules in the probed volume during an actual measurement and is evidence that single-molecule detection by SERS has been achieved. Spectra measured in 1 s collection time with 100 mW nonresonant 830 nm excitation provide a clear ''fingerprint'' of a single PIC molecule by showing its typical Raman lines between 700 and 1700 cm -1. Single-molecule Raman signals are also detected for the first time at the anti-Stokes side of the excitation laser. Effective Raman cross sections for PIC of 10 -16 cm2 per molecule can be inferred from the ratio between ''pumped'' anti-Stokes and Stokes signals.

178 citations


Journal ArticleDOI
TL;DR: In this article, the main heteroatoms in pollutants and chemical agents have been determined in atmospheric conditions with the use of the time-resolved laser-induced breakdown spectroscopy (TRELIBS) method.
Abstract: Detection limits for the main heteroatoms in pollutants and chemical agents have been determined in atmospheric conditions with the use of the time-resolved laser-induced breakdown spectroscopy (TRELIBS) method. This method presents many advantages for detection in hazardous or corrosive gas mixtures where sampling systems are not usable. Moreover, low concentrations of fluorine, chlorine, sulfur, and carbon can be measured with short analysis times. Currently, concentration limits are close to 10-50 ppm (w/w) for F, Cl, and C atoms, while presently only 1500 ppm (w/w) limits are reached for S. These measurements are obtained with an analysis time of under 20 s.

174 citations


Journal ArticleDOI
TL;DR: Colarusso et al. as discussed by the authors, PINA COLARUSSO, LINDA H. KIDDER, IRA W.K., I.W.C., L.H.L., E.N.C.
Abstract: BY PINA COLARUSSO, LINDA H. KIDDER, IRA W. LEVIN, JAMES C. FRASER, JOHN F. ARENS, AND E. NEIL LEWIS* LABORATORY OF CHEMICAL PHYSICS, NATIONAL INSTITUTE OF DIABETES AND DIGESTIVE AND KIDNEY DISEASES, THE NATIONAL INSTITUTES OF HEALTH, BETHESDA, MARYLAND 20892 (P.C., L.H.K., I.W.L., E.N.L.); VANGUARD RESEARCH, INC., FAIRFAX, VIRGINIA 22030 (J.C.F.); AND SPACE SCIENCES LABORATORY, UNIVERSITY OF CALIFORNIA, BERKELEY, CALIFORNIA 94720 (J.F.A.)

173 citations


Journal ArticleDOI
TL;DR: In this article, the effect of emission signal temporal development, sample translational velocity, number of spectra accumulated, laser pulse stability, detector gate delay, surface roughness, and use of background correction on LIBS precision was investigated.
Abstract: Several factors influence the precision of laser-induced breakdown spectroscopy (LIBS) measurements. This paper reports on the effect of emission signal temporal development, sample translational velocity, number of spectra accumulated, laser pulse stability, detector gate delay, surface roughness, and use of background correction on LIBS precision. The results are presented in two formats: within measurement/shot-to-shot precision (intra-measurement) and between measurement precision (inter-measurement). The data indicate that intra- and inter-measurement precision are optimized under different conditions. The best precision obtained was 0.03% .

170 citations



Journal ArticleDOI
TL;DR: In this paper, the authors used time-resolved laser-induced fluorescence for direct uranium speciation at low level in the framework of environmental studies, by varying pH and uranium concentration in the absence of carbonate ions and at fixed ionic strength.
Abstract: Time-resolved laser-induced fluorescence is a unique method for direct uranium speciation at low level in the framework of environmental studies. By varying pH and uranium concentration in the absence of carbonate ions and at fixed ionic strength, it was possible, together with free uranyl UO2 2+, to identify spectrally and temporally all the uranium-hydroxo complexes, namely, UO2 OH+, UO2 (OH)2 , UO2 (OH)3-, (UO2)2(OH)2 2+, (UO2)3(OH)5+, and (UO2)3(OH)7-.

144 citations


Journal ArticleDOI
TL;DR: In this paper, the authors present a few examples of typical patterns found in the synchronous and asynchronous spectra affected by those perturbations, including random noise, baseline fluctuations, band position, and width changes.
Abstract: It has been shown that the most common perturbations of conventional (one-dimensional) spectra such as random noise, baseline fluctuations, band position, and width changes may complicate two-dimensional (2D) correlation spectra, sometimes making them completely useless. In addition, two different physical causes may generate similar patterns for the synchronous and asynchronous spectra. Some of these effects, such as random noise and baseline fluctuations, can be eliminated from the input data, and one can recover the original appearance of 2D correlation spectra. The other effects, such as the frequency shift and bandwidth variation, cannot be removed from the experimental spectra. In this instance, the number and position of the correlation peaks can be elucidated by simulation studies. This report presents a few examples of typical patterns found in the synchronous and asynchronous spectra affected by those perturbations. Long streaks in 2D correlation spectra reveal extensive baseline fluctuations in the original data set. A simple offset often significantly reduces the extent of this effect. When no reasonable baseline correlations can be performed, the second derivative may solve this problem. In most cases, the perturbationaveraged spectrum is recommended as a reference. However, it has been proved that the calculation of 2D correlation spectra without any reference spectrum may also provide useful information, especially for data heavily influenced by noise or baseline fluctuations. In the majority of real-world systems, the spectral changes are a continuous function of applied perturbation. Thus, 2D correlation spectra yield information about the relative rate of intensity variations rather than the sequence of spectral events.

138 citations


Journal ArticleDOI
TL;DR: Diffuse reflectance spectroscopy of colonic tissue was employed to determine whether the spectra can be used to distinguish between neoplastic and non-neoplastic tissue in vivo and the mean predictive accuracies were found to be higher than expected.
Abstract: Diffuse reflectance spectroscopy of colonic tissue was employed to determine whether the spectra can be used to distinguish between neoplastic and non-neoplastic tissue in vivo. A total of 224 spectra were obtained in the wavelength range of 350-800 nm from 107 non-neoplastic tissue samples (84 normal mucosa, 23 hyperplastic polyps) and 53 neoplastic tissue samples (44 adenomatous polyps, 9 adenocarcinomas). Pattern recognition algorithms including multiple linear regression (MLR), linear discriminant analysis (LDA), and backpropagating neural network (BNN) were used to distinguish between the two tissue classes. The spectra were randomly separated into training and prediction sets for data analyses. The mean predictive accuracies of distinguishing neoplastic tissue from non-neoplastic tissue with MLR, LDA, and BNN were 85, 82, and 85%, respectively. In a similar fashion, the more clinically relevant problem of distinguishing adenomatous polyps from hyperplastic polyps was assessed. The mean predictive accuracies of distinguishing adenomatous polyps from hyperplastic polyps with MLR, LDA, and BNN were 85, 81, and 82%, respectively. The major spectral differences between tissues were attributed to changes in blood volume, oxygen saturation of hemoglobin, mean vessel depth within tissue, and tissue scattering.

Journal ArticleDOI
TL;DR: In this article, the application of standard two-way curve resolution methods for analysis of three-way Raman image data is reported for analysis and comparison of results for two real Raman images.
Abstract: The application of standard two-way curve resolution methods is reported for analysis of three-way Raman image data. Two current curve resolution methods are described: principal factor multivariate curve resolution (PF-MCR), which uses principal factor analysis (PFA) combined with varimax rotation and alternating leastsquares optimization (ALS), and orthogonal projection multivariate curve resolution (OP-MCR), which uses a Gram-Schmidt modified orthogonal projection approach (OPA) followed by ALS. The OPMCR technique is shown to be an extremely rapid method of analysis producing results equivalent to those of PF-MCR in one-third to one-fourth the time. The results from MCR analysis using either method provide the number of chemical species present in the sample, the spectrum of each species for identification, and the concentration image for each species. The additional benefit of image noise reduction also results from the MCR techniques. A brief description of the theory is presented followed by analysis and comparison of results for two real Raman image data. A discussion is given addressing the rapid analysis aspects of OP-MCR and the relative merits and drawbacks of the technique in comparison to PF-MCR. The use of data subsampling is also discussed as a way of decreasing analysis time without loss in accuracy or performance.

Journal ArticleDOI
TL;DR: In this paper, partial least squares regression analysis was used to build calibration models for three unique spectral data sets of glucose in water, which were then submitted to a one-factor PLS model that is limited to the 5975-5850 cm-1 spectral range.
Abstract: Partial least-squares (PLS) regression analysis was used to build calibration models for three unique spectral data sets of glucose in water. Spectra in the first data set were collected with a 2.0 mm optical pathlength. For these data, the measured root-mean-square (rms) noise of 100% lines over the 5975-5850 cm-1 spectral range was 4.5 micro-absorbance units (mu AU). Spectrometer upgrades permitted a 5.2 mm optical pathlength for the second data set, and the resulting spectra had an rms noise of 5.9 mu AU. Further spectrometer adjustments allowed the use of a 10.0 mm optical pathlength for the third data set, and the resulting spectral rms noise was 8.4 mu AU. In each case, the instrumentation was modified individually in order to provide high radiant powers at the detector while avoiding detector saturation. Poor calibration models for the first data set indicate that a 2.0 mm optical pathlength is insufficient for adequate glucose measurements at clinically relevant concentrations. Calibration and prediction errors for the data collected at 5.2 and 10.0 mm pathlengths ranged from 0.40-0.50 and 0.35-0.40 mM, respectively. Digital Fourier filtering significantly improved model performance by reducing the required number of latent variables (factors) in the PLS models and by reducing the wavelength dependency of these models. For the best calibration model, spectra in the data set corresponding to a 10.0 mm pathlength were Fourier filtered with a Gaussian-shaped filter defined in digital frequency units (f) by a mean position of 0.0206 f and a standard deviation width of 0.0031 f. These filtered spectra were then submitted to a one-factor PLS model that is limited to the 5975-5850 cm-1 spectral range. Consideration of different spectral ranges and an analysis of spectral loading vectors indicate that the 5920 cm-1 absorption band for glucose is critical for useful analytical measurements.

Journal ArticleDOI
TL;DR: In this paper, the authors proposed a probe head for Raman spectroscopy that is suitable for use on a spectrometer deployed by a rover or a lander on the surface of a Mars, the Moon, or an asteroid.
Abstract: Raman spectroscopy has the potential to provide definitive identification and detailed characterization of the minerals that comprise rocks and soils on planetary surfaces. We have designed a probe head for Raman spectroscopy that is suitable for use on a spectrometer deployed by a rover or a lander on the surface of a planet such as Mars, the Moon, or an asteroid. The probe head is lightweight, low power, rugged, and simple. It is based on a tiny distributed feedback diode laser and volume holographic components. A protective shell surrounds the probe head and serves as a mechanical stop for the mechanical arm of a planetary rover or lander during placement of the probe head onto the surface of a rock or soil. Pressing the shell against the rough surface of a target rock or soil also places the sampling objective of the probe head in rough focus, and the probe head is designed to be tolerant of focusing errors of 5 mm. A breadboard version of the probe head gave spectra of high quality on clean crystals of diamond, sulfur, calcite, quartz, and olivine. The results are qualitatively comparable to those obtained by using a conventional micro-Raman spectrometer on fine-grained travertine and on difficult specimens of basaltic lavas and impactites whose original mineralogy had been altered by reaction with water and air.

Journal ArticleDOI
TL;DR: In this paper, the theoretical and experimental implications of tapering a multimode optical fiber with a view to its use in evanescent wave absorption spectroscopy were discussed, showing the possibility of quadruplicating the absorbance efficiency.
Abstract: This paper discusses the theoretical and experimental implications of tapering a multimode optical fiber with a view to its use in evanescent wave absorption spectroscopy. Good experimental results are obtained, showing the possibility of quadruplicating the absorbance efficiency. This easy and reproducible technique for taper fabrication is suitable for the implementation of both probes for spectroscopy and chemically assisted fiber-optic sensors.

Journal ArticleDOI
TL;DR: In this paper, the capability of FT-IR transmission spectrometry was examined for the direct determination of glucose in whole blood without any sample preparation, where the whole blood samples were automatically aspirated by a syringe pump into the transmission cell.
Abstract: The capability of FT-IR transmission spectrometry was examined for the direct determination of glucose in whole blood without any sample preparation. For these investigations, the whole blood samples were automatically aspirated by a syringe pump into the transmission cell. Infrared spectra were recorded in the 1500-900 cm-1 range. Despite the high water background absorption and the complex blood matrix, significant spectral changes due to different glucose concentrations were observed. Chemometric (partial leastsquares) models were applied for the determination of glucose. A standard error of calibration of 13.8 mg/dL was obtained by using a partial least-squares calibration model containing five ranks. The residues for an independent test set were less than 15 mg/dL.

Journal ArticleDOI
TL;DR: In this paper, the potential for noninvasive determinations of glucose, lactate, and ammonia in cell culture media was investigated through near-infrared spectroscopy of the 2.0-2.5 mu m combination region.
Abstract: The potential for noninvasive determinations of glucose, lactate, and ammonia in cell culture media was investigated through near-infrared spectroscopy of the 2.0-2.5 mu m combination region. Samples taken from a three-day fibroblast culture were analyzed with standard clinical chemistry techniques and with a Fourier transform infrared spectrometer. The data were analyzed in three phases in an attempt to solve problems of correlation in the data. First, partial least-squares regression was used to build a multivariate calibration model based on the near-infrared spectra of the cell culture media and measured reference values. Second, an independent calibration was performed with aqueous mixtures of glucose, lactate, ammonia, glutamate, and glutamine. Finally, a calibration using a combination of spectra from cell culture media samples and aqueous mixtures was performed. In each case, the spectral loadings obtained from the calibration were inspected to determine the extent of weighting given to different spectral regions. The results indicate that a selective calibration model can be produced by combining data from samples of different type. Prediction errors of 2, 8, and 15% were obtained for glucose, lactate, and ammonia, respectively.

Journal ArticleDOI
TL;DR: In this paper, a fiber-optic probe for remote laser-induced breakdown spectroscopy (LIBS) and Raman imaging has been developed for the microanalysis of solid samples.
Abstract: A fiber-optic probe designed for remote laser-induced breakdown spectroscopy (LIBS), Raman spectroscopy, and Raman imaging has been developed for the microanalysis of solid samples. The probe incorporates both single-strand optical fibers and an image guide and allows atomic emission and Raman analysis of any spot on a solid sample within a 5 mm diameter field of view. The real-time sample imaging aspects of the probe are demonstrated by measuring LIBS spectra from different regions of a granite sample and by measuring the Raman spectra of individual TiO2 and Sr(NO3)2 particles on a soil substrate. The ability to obtain remote Raman images of the TiO2 and Sr(NO3)2 particles on the soil substrate is also demonstrated. In this paper we discuss the design and implementation of the fiber-optic probe for obtaining LIBS spectra, Raman spectra, and Raman images.

Journal ArticleDOI
TL;DR: In this article, a Nd:YAG laser operating at 60 mJ/pulse was focused onto the surface of the liquid, and the laser-induced breakdown spectroscopy was used to determine detection limits for nickel and chlorinated hydrocarbons.
Abstract: Spectrochemical analyses of aqueous solutions containing nickel or the chlorinated hydrocarbons (CHCs) C2Cl4, CCl4, CHCl3, and C2HCl3 were performed with the use of laser-induced breakdown spectroscopy. A Nd:YAG laser operating at 60 mJ/pulse was focused onto the surface of the liquid. Elemental line intensities were monitored in the laser-produced plume as a function of analyte concentration to determine detection limits. The limits of detection for nickel in water were 36.4 +/- 5.4 mg/L and 18.0 +/- 3.8 mg/L for laser irradiation at 1.06 mu m and 355 nm, respectively. Ablation of pure CHCs at 355 nm produced extremely intense plasma emissions that primarily consisted of spectroscopic features attributed to CN, C3, H, N, and Cl. The spectra were structurally identical for all the CHCs except for differences in the intensities of various emission lines. With the use of emission from neutral atomic chlorine as an identifier for CHC contamination of water, no detectable traces of these elements were observed in saturated aqueous solutions. The detection limits for the CHCs were well above the saturation limits of CHC in water.

Journal ArticleDOI
TL;DR: In this paper, the design and characterization of a simple and robust hyperspectral Raman line imaging illumination system with the use of a Powell lens is reported. And significant decreases in image acquisition time are also reported with the using of a prismatic lens-illuminated HRL imaging microscope equipped with an intensified charge-coupled device (CCD) detector.
Abstract: The design and characterization of a simple and robust hyperspectral Raman line imaging illumination system with the use of a Powell lens is reported. The generated line uniformity is +/- 5% of total intensity with a laser power density of 12 mW/ mu m2 at the sample with a 50X/0.8 NA (numerical aperture) objective. Similar results were obtained by using other objectives. Linewidths remained near the diffraction limit for all objectives tested. Significant decreases in image acquisition time are also reported with the use of a Powell lens-illuminated hyperspectral Raman line imaging microscope equipped with an intensified charge-coupled device (CCD) detector. Hyperspectral images (100 X 350 pixels) were acquired in as little as 8 with a corresponding signal-to-noise ratio of 24.

Journal ArticleDOI
TL;DR: In this paper, the Stark broadening of emission lines was used to determine the electron density and the ratio of line intensities was exploited for the determination of electron temperature, and the dependence on electron temperature and density on different experimental parameters such as distance from the target, delay time after the initiation of the plasma, and laser irradiance was also discussed in detail.
Abstract: Spectroscopic studies of laser-induced plasma from a high-temperature superconducting material, viz., YBa2 Cu3 O7(YBCO), have been carried out. Electron temperature and electron density measurements were made from spectral data. The Stark broadening of emission lines was used to determine the electron density, and the ratio of line intensities was exploited for the determination of electron temperature. An initial electron temperature of 2.35 eV and electron density of 2.5 X 10 17 cm-3 were observed. The dependence on electron temperature and density on different experimental parameters such as distance from the target, delay time after the initiation of the plasma, and laser irradiance is also discussed in detail.

Journal ArticleDOI
TL;DR: A confocal direct imaging Raman microscope (CDIRM) based on two synchronized scanning mirrors, a monochromator, and two charge-coupled device (CCD) cameras has been developed as discussed by the authors.
Abstract: A confocal direct imaging Raman microscope (CDIRM) based on two synchronized scanning mirrors, a monochromator, and two charge-coupled device (CCD) cameras has been developed With this system it is possible to make both Raman spectra of a small measurement volume and images of a larger sample area in one specific Raman band The spatial resolution of the system was determined for two limiting situations: a small sphere and a thin layer The image of a 0282 μm sphere appeared to have a full width at half-maximum (FWHM) of 12 μm in the axial and 037 μm in the lateral direction, whereas the image of a 275 nm layer showed an FWHM of 14 μm in the axial direction Confocal Raman images were made of the DNA and protein distribution in polytene chromosomes with a relatively weak Raman signal [01 photons/(second·pixel)] Further, a three-dimensional Raman image of the drug distribution in a phthalocyanine-incubated fixed cell is presented These examples show that the CDIRM can be used to image samples with a weak Raman signal and that three-dimensional images of the distribution of specific molecules in a sample can be made

Journal ArticleDOI
TL;DR: In this paper, the authors used NIR reflectance spectroscopy to differentiate water in different hydrogen-bonding environments of skin in vivo and to determine the effect of moisturizer application on water content.
Abstract: Near-infrared (NIR) reflectance spectroscopy has been used to differentiate water in different hydrogen-bonding environments of skin in vivo and to determine the effect of moisturizer application on water content. Four types of water have been observed in the second-derivative spectrum of skin. These are assigned as water associated with the lipid bilayers, primary and secondary water of hydration on protein, and bulk (free) water in deeper tissue. The intensities of the lipid-associated water band and the bulk water band depend on anatomical site. The latter, particularly, may be affected by corneocyte size and may have potential in predicting transdermal penetration of drugs. Moisturizer application appears to have little effect on water content, but results in changes in the degree of scattering of radiation, suggesting that moisturizers smooth, rather than hydrate, the skin.

Journal ArticleDOI
TL;DR: In this article, the infrared spectrum of a sample in a saline solution cannot be retrieved adequately when the spectrum of pure water is subtracted Some water bands remain in the spectrum, while the concentration of the salt is unknown, it is still possible to obtain a good spectrum of the sample free of water.
Abstract: The infrared (IR) spectrum of a sample in a saline solution cannot be retrieved adequately when the spectrum of pure water is subtracted Some water bands remain in the spectrum The retrieved spectrum is good only when the spectrum of NaCl in water at the right concentration is subtracted However, when the concentration of the salt is unknown, it is still possible to obtain a good spectrum of the sample free of water This is done by subtracting from the original spectrum a fraction of two eigenspectra of water: one for pure water and one for NaCl solvated water The fraction of the eigenspectra is determined with the 2100 and 3300 cm -1 bands The effectiveness of the method is illustrated with a solution of sodium monochloroacetate in a saline solution

Journal ArticleDOI
TL;DR: In this article, the influence of laser beam properties (pulse width, wavelength, and power density) on fractional laser ablation was investigated, and the behavior of the Zn/Cu ratio vs. laser power density was shown.
Abstract: The Zn-to-Cu ratio in brass was measured by laser ablation inductively coupled plasma atomic emission spectroscopy. The influence of laser beam properties (pulse width, wavelength, and power density) on fractional laser ablation was investigated. The behavior of the Zn/Cu ratio vs. laser power density shows that there are different mechanisms influencing ps and ns laser ablation. With the use of a 30 ns pulse duration from an excimer laser, thermal vaporization appears to be the dominant process in the low-power density region. The Zn/Cu ratio approaches stoichiometry at higher power density, but the ablated mass still remains Zn rich. With a 35 ps pulse Nd:YAG laser, a nonthermal mechanism appears to govern the laser ablation process. When a 3 ns Nd:YAG laser is used, both thermal and nonthermal processes exist. For both 3 ns and 30 ps Nd:YAG lasers, stoichiometric ablation can be achieved at higher power densities.

Journal ArticleDOI
TL;DR: In this article, the distribution of pure compounds in the blend can be investigated by looking at the score plot for the first two principal components (PCs), the contribution of each variable to the dissimilarity and, in particular, the contrasts between two characteristic wavelengths for each compound.
Abstract: Powder blending was monitored on-line by taking near-infrared measurements at regular time intervals during the mixing process. The average standard deviation between the measurements taken at each time and the dissimilarity between each mixture spectrum and the ideal mixture spectrum were used to monitor the changes in the powder blend over time. The distribution of the pure compounds in the blend can be investigated by looking at the score plot for the first two principal components (PCs), the contribution of each variable to the dissimilarity and, in particular, the contrasts between two characteristic wavelengths for each compound. Statistical process monitoring charts were used to determine the blending time at which the mixture was within (spectroscopic) specifications. Shewhart charts monitor the blend at characteristic wavelengths for each substance separately. The Hotelling's T2 test defines a multivariate confidence interval. For spectral data, feature reduction is needed. This procedure is accomplished by using characteristic wavelengths for the pure compounds or the significant PCs after performing principal components analysis (PCA).

Journal ArticleDOI
TL;DR: In this article, the authors introduce basic relevant engineering concepts to chemists who are already familiar with modern analytical technology, and describe how process analyzers compare with laboratory instrumentation, and how they differ from more traditional laboratory-based analysis.
Abstract: The aim of this Focal Point Article is to answer a question frequently posed by laboratory analytical chemists: What is process analytical chemistry and how does it differ from more traditional laboratory-based analysis? Although there are many books and papers on process analytical chemistry, most are written to introduce general analytical concepts to process engineers. Our goal here is the reverse: to introduce basic relevant engineering concepts to chemists who are already familiar with modern analytical technology, and to describe how process analyzers compare with laboratory instrumentation. The stakes are very high since process analyzers are becoming more important to the manufacturing industry for improved process uptimes, safety, yields, and

Journal ArticleDOI
TL;DR: In this paper, a novel sensor for quantifying molecular O2 based entirely on solidstate electronics is presented, which is based on the luminescence quenching of tris(4,7-diphenyl-1, 10-phenanthroline)ruthenium(II) ([Ru(dpp)3]2+) by molecular O 2.
Abstract: A novel sensor for quantifying molecular O2 based entirely on solidstate electronics is presented. The sensor is based on the luminescence quenching of tris(4,7-diphenyl-1, 10-phenanthroline)ruthenium(II) ([Ru(dpp)3]2+) by molecular O2. The sensor involves immobilizing the ruthenium complex within a porous sol-gel-processed glass film and casting this film directly onto the surface of a blue quantumwell light-emitting diode (LED). The ruthenium complex is excited by the LED, the [Ru(dpp)3]2+ emission is filtered from the excitation with a low-cost acrylic color filter, and the emission is detected with an inexpensive silicon photodiode. The sensor response to gaseous O2 and dissolved O2 in water is presented. The sensor exhibits fast response times and good reversibility, and detection limits are 0.5% , 0.02% , and 110 ppb, respectively, for O2 in the gaseous (linear Stern-Volmer and multi-site Stern-Volmer analysis) and aqueous phase. This sensor provides a cost-effective alternative to traditional electrochemical-based O2 sensing and also provides a platform for other optically based sensors.

Journal ArticleDOI
TL;DR: In this article, the authors compared data preprocessing and direct standardization for the determination of the component concentrations in a ternary mixture of methanol, ethanol, and 1-propanol using NIR spectroscopy.
Abstract: Recently, efficient methods have become available to transfer a multivariate calibration model from one instrument to another. Two categories can be distinguished: improvement of the robustness of the calibration model by, for example, a proper data preprocessing; and adaptation of the calibration model by, for example, (piecewise) direct standardization. In direct standardization, a subset from the calibration set should be measured on both instruments. Usually, however, the calibration samples cannot be measured on both instruments. When data preprocessing is applied to the transfer of multivariate calibration models, there is no need for remeasurement of a subset on both instruments. In this paper, both categories are compared for the determination of the component concentrations in a ternary mixture of methanol, ethanol, and 1-propanol using NIR spectroscopy. The calibration models obtained on one instrument are transferred to other NIR instruments. It has been found that the results of proper data preprocessing are comparable with the results obtained by direct standardization when the models are transferred over three NIR instruments.

Journal ArticleDOI
TL;DR: In this paper, an optical effect in the infrared that can be used to image the interface specifically was observed, and it was shown that the properties of the interface can be specifically altered by the application of an electric potential across the sample.
Abstract: For phase-separated multicomponent polymeric systems, characterization of the interface between the components is particularly challenging. We have observed an optical effect in the infrared that can be used to image the interface specifically. This method yields images of the interfaces based on the interfaces showing apparent absorption arising from changes in refractive index at frequencies far from the specific frequencies associated with the components of the mixture. This method has been applied to multicomponent samples of polymer-dispersed liquid crystals where the nature of the interface can be specifically altered by the application of an electric potential across the sample. Effects of this optical phenomenon on spectra from such multicomponent systems are discussed, and factors that complicate quantitative analysis of data from interfacial regions have been pointed out.