用紫外-可见光检测器进行色谱峰的光谱分析方法

采用紫外－可见光检测器和自编吸收光谱分析程序对色谱峰在１９５～７００ｎｍ波长范围内进行扫描,得到样品和标准品的吸收光谱图,通过对二者进行比较来鉴定色谱峰纯度,操作简便,具有一定的实用价值。     

Quantitative Auger electron spectroscopic analysis of carbides,nitrides and carbonitrides

A novel method for the quantitative evaluation of Auger electron spectra based on peak areas is presented. Sample and reference spectra in integral mode are filtered by an area conserving digital filter. This transforms the peak shapes influenced by chemical effects into standard peak shapes. After filtering a linear combination of reference spectra, differentiated spectra accounting for peak shifts and some low order polynomials to account for variations in the background is fitted to the sample spectrum by a least squares method. The need to approximate the spectrum of the secondary electron background explicitly for direct calculation of peak areas is thus eliminated. Filters of different widths are applied to reduce errors by chemical effects. The composition of the sample is computed from the composition of the reference samples and the coefficients obtained from the fit.To demonstrate the validity of this technique it has been applied to both, Gaussian model peaks and spectra of titanium carbonitrides. A further test on an alloy series is under investigation. The results show that the method works as predicted and gives accurate quantification.     

Resampling and deconvolution of linear time-of-flight records for enhanced protein profiling

We have developed a peak deconvolution strategy that is applicable to the full mass range of a time-of-flight (TOF) spectrum. This strategy involves resampling a spectrum to create a time series that has equal peak widths (in time) across the entire spectrum, and then using the deconvolution filters we have previously described. We use this technique to deconvolve the protein mass spectra for blood serum and cell lysates acquired on three separate TOF instruments. Following deconvolution, we resolve spectral structures consistent with expected events such as multiply charged ions, matrix adducts and post-translational protein modifications. The deconvolution procedure produces a 40% improvement in the resolution and enhanced experimental sensitivity over the full length of the linear TOF record, up to m/z 150 000. This approach is particularly appropriate for automated data analysis and peak detection in dense TOF spectra.     

Application of Computer-Aided Spectral Deconvolution Technique in Validation of High Performance Liquid Chromatographic Peaks

Abstract

Reliable analysis with high performance liquid chromatography (HPLC) requires purity of the eluting peak. The present work has combined the advantages of the availability of full spectral data from HPLC photodiode array UV detector and computer algorithms to perform chromatographic peak purity check. A deconvolution technique based on multicomponent analysis has been applied to the UV spectra of co-eluting components. This method employs residual error (Relative-fit-error, RFE) between predicted spectrum and analyte's spectrum to detect presence of other component or contaminant. Typical RFE values for uncontaminated chromatographic peaks of norethisterone and ethynyloestradiol range between 1 and 3, while contaminated peaks have RFE values as large as 145. A systematic increase in ‘relative-fit error’ from 1.10 to 145 was observed for peaks of norethisterone when contaminated to varied extent with ethynyloestradiol. Extent of peak overlap in chromatogram was also mapped out with this technique. The co-prescribed oral contraceptive, norethisterone and ethynyloestradiol were used as model in this work. An advantage of the method is its applicability when the contaminant's spectrum is unavailable. The method, unlike several earlier techniques, is also applicable to chromatograms with concidental elution time for the components.     

SDAT: analysis of <Superscript>131m</Superscript>Xe with <Superscript>133</Superscript>Xe interference

The Spectral Deconvolution Analysis Tool (SDAT) software was developed at The University of Texas at Austin. SDAT utilizes a standard spectrum technique for the analysis of β–γ coincidence spectra. Testing was performed on the software to compare the standard spectrum analysis technique with a region of interest (ROI) analysis technique. Experimentally produced standard spectra and sample data were produced at the Nuclear Engineering Teaching Laboratory (NETL) TRIGA reactor. The results of the testing showed that the standard spectrum technique had lower errors than the ROI analysis technique for samples with low counting statistics. In contrast, the ROI analysis technique outperformed the standard spectrum technique in high counting statistics samples. It was also shown that the standard spectrum technique benefitted from a compression of the number of channels within the spectra.     

FTIR microscopy of biological cells and tissue: data analysis using resonant Mie scattering (RMieS) EMSC algorithm

Transmission and transflection infrared microscopy of biological cells and tissue suffer from significant baseline distortions due to scattering effects, predominantly resonant Mie scattering (RMieS). This scattering can also distort peak shapes and apparent peak positions making interpretation difficult and often unreliable. A correction algorithm, the resonant Mie scattering extended multiplicative signal correction (RMieS-EMSC), has been developed that can be used to remove these distortions. The correction algorithm has two key user defined parameters that influence the accuracy of the correction. The first is the number of iterations used to obtain the best outcome. The second is the choice of the initial reference spectrum required for the fitting procedure. The choice of these parameters influences computational time. This is not a major concern when correcting individual spectra or small data sets of a few hundred spectra but becomes much more significant when correcting spectra from infrared images obtained using large focal plane array detectors which may contain tens of thousands of spectra. In this paper we show that, classification of images from tissue can be achieved easily with a few (<10) iterations but a reliable interpretation of the biochemical differences between classes could require more iterations. Regarding the choice of reference spectrum, it is apparent that the more similar it is to the pure absorption spectrum of the sample, the fewer iterations required to obtain an accurate corrected spectrum. Importantly however, we show that using three different non-ideal reference spectra, the same unique correction solution can be obtained.     

子窗口分析法用于偶氮染料GC-MS重叠峰的解析

 将子窗口因子分析法 (SWFA)应用于GC MS联用检测数据分析 ,并以两种偶氮染料 3,3′ 二氯联苯胺和 4,4′ 次甲基 双 (2 氯苯胺 )重叠图谱为例进行了解析。结果表明 ,此方法可直接进行目标组分的质谱分辨 ,得到目标组分的质谱图 ,进而得到该组分的色谱图。其结果准确、可靠。与窗口因子分析相比 ,子窗口的选择更加容易 ,人工干预少 ,解析速度快。     

Maintaining Accuracy in Gamma-Ray Spectrometry at High Count Rates

Gamma-ray spectrometry losses through pulse processing dead time and pile-up are best assayed with an external pulse technique. In this work, the virtual pulse generator technique as implemented commercially with the Westphal loss free counting (LFC) module is set up and tested with four high resolution gamma-ray spectrometers. Dual source calibration and decaying source techniques are used in the evaluation of the accuracy of the correction technique. Results demonstrate the reliability of the LFC with a standardized conventional pulse processing system. The accurate correction during high rate counting, including during rapid decay of short lived activities, has been the basis for highly precise determinations in reference materials studies.     

Localization and coherent dynamics of excitons in the two-dimensional optical spectrum of molecular J-aggregates

Two-dimensional optical spectra of J-aggregates at low temperature provide a large amount of information about the nature and dynamics of exciton states that is hidden in conventional broad band pump-probe spectra. By using numerical simulations, we study the two-dimensional absorption spectrum and find that it is dominated by a V-shaped negative peak and a blueshifted elliptic positive peak. We demonstrate a simple method to derive the energy dependence of the exciton localization size from the distance between these two features in the zero waiting time experiment. When the waiting time is turned on, the V peak is filled with an extra positive peak resulting from population relaxation. From the time evolution of this peak, energy dependent relaxation rates can be obtained. The oscillations of coherent contributions to the two-dimensional spectrum are not damped by inhomogeneous mechanisms and can be seen clearly.     

Activation analysis with standards containing two or more active nuclides A computerized method of calculation involving decay and gamma spectral resolution

The resolution of the gamma spectra of activities induced in materials by fast neutron, charged particle and gamma photon activation is complicated by the fact that many elements produce more than one active nuclide in significant amounts. Direct resolution by least-squares fitting of the spectra of standards is only possible in these circumstances if the standard and sample spectra are obtained at the same time after irradiation, as the shapes of the standard spectra change with time. An alternative to the practical collection of spectra in this way is the correction of the standard spectra to the mid-time of counting of a sample spectrum. This may be achieved by recording spectra for a standard at different times and resolving the decay curves obtained for each channel on the basis of the half-lives of the component nuclides, which may be decay-independent or related or both. From the component nuclide count-rates in each channel at some arbitrary time, the standard spectrum at the time of counting of the sample can be generated and then used in a conventional least squares-fit of the sample spectrum. A FORTRAN IV program has been written to carry out this type of calculation on an IBM 360 65 computer. The feasibility of using this method is demonstrated by its application to activation analyses involving standards containing decay-related and independent nuclides.     

Ultrahigh-resolution (1)H-(13)C HSQC spectra of metabolite mixtures using nonlinear sampling and forward maximum entropy reconstruction

To obtain a comprehensive assessment of metabolite levels from extracts of leukocytes, we have recorded ultrahigh-resolution 1H-13C HSQC NMR spectra of cell extracts, which exhibit spectral signatures of numerous small molecules. However, conventional acquisition of such spectra is time-consuming and hampers measurements on multiple samples, which would be needed for statistical analysis of metabolite concentrations. Here we show that the measurement time can be dramatically reduced without loss of spectral quality when using nonlinear sampling (NLS) and a new high-fidelity forward maximum-entropy (FM) reconstruction algorithm. This FM reconstruction conserves all measured time-domain data points and guesses the missing data points by an iterative process. This consists of discrete Fourier transformation of the sparse time-domain data set, computation of the spectral entropy, determination of a multidimensional entropy gradient, and calculation of new values for the missing time-domain data points with a conjugate gradient approach. Since this procedure does not alter measured data points, it reproduces signal intensities with high fidelity and does not suffer from a dynamic range problem. As an example we measured a natural abundance 1H-13C HSQC spectrum of metabolites from granulocyte cell extracts. We show that a high-resolution 1H-13C HSQC spectrum with 4k complex increments recorded linearly within 3.7 days can be reconstructed from one-seventh of the increments with nearly identical spectral appearance, indistinguishable signal intensities, and comparable or even lower root-mean-square (rms) and peak noise patterns measured in signal-free areas. Thus, this approach allows recording of ultrahigh resolution 1H-13C HSQC spectra in a fraction of the time needed for recording linearly sampled spectra.     

A Check Total for Validating Standardless and Normalised EDX Analysis at Low kV

Overlay of fitted peaks on spectra or goodness of fit indices do not always reveal element misidentifications and cannot confirm accuracy of composition, particularly at low kV where there are often strong peak interferences. The conventional Analysis Total requires beam current stability and measurement of at least one standard and is not available if results have to be normalised. If an accurate method is available to predict theoretical spectra, consistency of the peak and background content in spectra can be used to validate analyses even when results are normalised. A new Check Total is proposed that has properties similar to the conventional Analysis Total and can be used to validate a normalised set of concentrations. Check Total is calculated from the ratio of (total area of peaks/total background area) in observed and theoretically simulated spectra. If peak to total background can be predicted with an accuracy of 10% standard deviation, Check Total is useful for alerting the analyst to missing peaks, deconvolution errors at low kV and specimen charging. More accurate spectrum synthesis would make Check Total also sensitive to small errors in microscope kV calibration.     

Computer identification of infrared spectra by correlation-based file searching

A new method for the computerized search and identification of infrared spectra has been developed and evaluated. Based on cross-correlation, the search system utilizes all spectral information in a digitized spectrum when it attempts to match an unknown spectrum to one in a small library of known spectra. To evaluate a spectral match, the search program calculates the cross-correlation function between the unknown and known (library) spectra which indicates their degree of similarity and allows library spectra to be ranked in order of probability of match to the unknown spectrum. In this study, several small infrared spectral libraries of structurally similar compounds were searched under conditions which examined the sensitivity of the search method to chemical and instrumental variations. Because the correlation technique is slower than conventional file-searching methods, it will probably find greatest use in the search of small collections of similar spectra or as a match-ranking procedure following preliminary selection by a faster search method.     

Photolysis-assisted, long-path FT-IR detection of air pollutants in the presence of water and carbon dioxide

Seven important air pollutants have been investigated by photolysis-assisted FT-IR spectroscopy. This technique renders invisible the spectra of water and carbon dioxide, which are two of the main concerns in long-path infrared spectroscopy. A cell, equipped with a UV lamp, was used to oxidise the analyte in the air sample and the spectrum recorded was used as a new background for the original sample spectrum. The optimum UV irradiation time and correctness of the concentrations were determined for this technique and compared with those from traditional methods. The signal-to-noise (S/N) ratios of the so-called “shadow spectra” were better than, or at least comparable to, the S/N ratios in the absorbance spectra obtained by using as background an air or an evacuated cell reference and subtraction of the spectra of water and carbon dioxide from a spectral library. The detection limits for the volatile organic compounds investigated have been improved by using this new method in which an appropriate background spectrum can be obtained quickly. The limitations of the method are that it cannot be applied to non-UV reactive compounds, such as methane, and the detection limits can be appreciably degraded when bands due to ozone in the shadow spectra overlap with those of the compounds under investigation.     

A spectrum stripping method for the computer-coupled activation analysis of unknown samples by γ-ray spectrometry

A spectrum stripping method for the computer-coupled activation analysis of unknown samples using γ-ray spectrometry is discussed. Before the unscrambling of the γ-ray is performed using standard spectra of the components, each spectrum is smoothed, statistically weighted and corrected for background. The photopeaks of the standard spectra are then aligned with the respective peaks of the sample spectrum, one at a time after correcting for gain drift if necessary, and the undesired components are stripped out. After successive subtraction, the characteristic spectrum of the desired element is compared with that of the standard to determine its weight. The results obtained using the present method are as good as those obtained from least-squares analysis in ideal cases, but appear to be better when assumptions inherent in the least-squares method are no longer valid.     

FTIR of touch imprint cytology: a novel tissue diagnostic technique

Fourier transform infrared spectroscopic (FTIR) interrogation of biological tissues in real time has largely been a challenging proposition because of the strong absorption of mid-infrared light in water filled tissues. To enable sampling of tissues they must be sectioned and dried, which has time and resource implications. FTIR of touch imprint cytology (TIC) has been proposed to circumvent this problem. TIC is a well known histopathological method of rapidly analysing biological tissues. In this article we demonstrate the ability of FTIR of TIC to provide detailed spectra which can be used to differentiate various tissue pathologies. FTIR spectral profiles of TIC of lymph node and thyroid tissues differ visually when compared with TIC spectra of parathyroid tissue. The lymph node showed strong lipid spectral peaks at 1166cm(-1) and 1380cm(-1) including a very strong carbonyl-ester band at 1748cm(-1), and a strong methylene bending band (scissoring, at 1464cm(-1)). Smaller intensity protein peaks at 1547cm(-1) and 1659cm(-1) were also seen. The thyroid spectra, in addition to evident strong protein peaks at 1547cm(-1) and 1659cm(-1), also demonstrated possible nucleic acid signals at 1079cm(-1) and 1244cm(-1). The C-OH peak at 1037cm(-1) was attributed to carbohydrate signals. Parathyroid adenoma showed a marginal shift to lower wavenumbers with decreased amide I and II peak intensities when compared to hyperplasia. Nucleic acid peak positions at 1079cm(-1) and 1244cm(-1) were of higher intensity in adenomas compared to hyperplastic glands possibly demonstrating an increase in cell proliferation and growth. This study demonstrates the feasibility of cytoimprint FTIR for the intraoperative diagnosis of tissue during surgical neck exploration for the management of hyperparathyroidism. There is potential for the application of the technique in sentinel lymph node biopsy diagnosis and tumour margin evaluation.     

Calculation of polymer blend compositions from Raman spectra: A new method based on parameter estimation techniques

A simple method to determine polymer blend compositions from their Raman spectra is presented. The method is based on expanding linearly the experimentally measured Raman spectrum of the blend, in terms of Raman spectra of pure components. A smooth function has also been included in the linear expansion to take into account the fluorescence interference, inherent to Raman spectroscopy. The coefficients of the linear expansion that give the best fit to the experimentally measured Raman spectrum of the blend are found by using a standard method of parameter estimation (Marquardt–Levenberg). These coefficients are directly related to the blend composition via a simple calibration procedure. Unlike standard methods of processing Raman spectra as deconvolution and curve‐fitting—which use Gaussian and/or Lorentzian functions to approximate the spectrum bands—the proposed method does not require either baseline correction or previous knowledge of peak parameters. Also, this method requires less CPU time than deconvolution and curve‐fitting procedures, and it is easy to automate. The proposed method has been applied to blends made out of two polymers: Polystyrene (PS) and poly(phenylene oxide) (PPO), to test its precision and consistency. Excellent agreement was found between calculated and expected blend compositions. Also, the reconstructed spectra agree very well with the experimentally measured blend spectra. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 1013–1023, 2000     

Numerical taxonomy and information theory applied to feature selection from filed infrared spectra for automated interpretation

A method is described for the selection of features from infrared spectra, aimed at computer-aided interpretation by retrieval of coded spectra. The coding procedure is similar to that of the ASTM Infrared Spectral Index, involving 140 binary-coded wavelength inter-vals (peak positions) of 0.1 μm for each spectrum (Wyandotte code). In addition to this procedure, windows of 0.3 μm and 0.5 μm are used. For a given set of spectra, the peak positions are grouped by means of numerical taxonomy; the correlation coefficient is used as a criterion. Information contents of all peak positions are calculated with Shannon's formula. One peak position is selected from each group, viz. the position having the highest information content. The selection obtained in this way is composed of peak positions that are weakly correlated yet yield much information. The spectra are then coded again, taking account of the selected peak positions only. In order to evaluate the selection, the number of spectra still differing from all other spectra in the set is determined by comparing all reduced spectra with each other. For a file of 395 spectra (hydrocarbons, alcohols, ethers, carbonyl compounds) 99.0% of the spectra are unique when 27 selected features are used. For a file of 5100 spectra (of a wide variety of compounds, taken from the ASTM Infrared Spectral Index) 97.7% of these spectra are unique when only 40 out of all 140 peak positions are used.     

Parallels between multiple population-period transient spectroscopy and multidimensional coherence spectroscopies

We have recently shown that homogeneous and heterogeneous kinetics can be distinguished by experiments that compare the evolution of the population of a state over two time intervals [E. van Veldhoven et al., ChemPhysChem 8, 1761 (2007)]. This paper elaborates on the analogy between these multiple population-period transient spectroscopy (MUPPETS) experiments and more familiar spectroscopies based on the evolution of coherences. Using a modified inverse-Laplace transform, a standard kinetics decay is re-expressed as a "rate spectrum." A nonexponential decay creates a linewidth in this spectrum. Mechanisms for line broadening in rate spectra are compared to those for line broadening in frequency-domain spectra. Homogeneous and heterogeneous kinetics are defined precisely and are shown to be the counterparts of homogeneous and inhomogeneous line broadenings in frequency-domain spectra. Homogeneous line broadening mechanisms are further divided into equilibrium and nonequilibrium mechanisms, with equilibrium mechanisms more prevalent in frequency spectra and nonequilibrium mechanisms more prevalent in rate spectra. Spectral representations of two-dimensional MUPPETS experiments are developed that are equivalent to two-dimensional coherence spectroscopies. In particular, spectra equivalent to hole-burning and to correlation spectra are defined. Frequency-domain spectra are often modeled as an inhomogeneous distribution of identical homogeneous line shapes. A parallel homogeneous-heterogeneous model for kinetics is defined. Within this model, MUPPETS has sufficient information to completely separate the homogeneous and heterogeneous contributions to a nonexponential decay, even when the homogeneous contribution is nonexponential.     

Outlier detection for the Generalized Rank Annihilation Method in HPLC-DAD analysis

The Generalized Rank Annihilation Method (GRAM) is a second-order calibration method that is used in chromatography to quantify analytes that coelute with interferences. For a correct quantification, the peak of the analyte in the standard and in the test sample must be aligned and have the same shape (i.e., have a trilinear structure). Variations in retention time and shape between the two peaks may cause the test sample to behave as an outlier and produce an incorrect prediction. This situation cannot be detected by checking the coincidence of the recovered spectrum with the known spectrum of the analyte because the spectral domain is not affected. It cannot be detected either by checking if the recovered profile is correct (i.e., unimodal and positive). Several plots are presented to detect such outliers. The first plot compares the particular elution profiles in the standard and in the test sample that are recovered by least-squares regression from the spectra estimated by GRAM. The calculated elution profiles from both peaks should coincide. A second plot uses the elution profiles and spectra calculated by GRAM to define the vector space spanned by the interferences. The measured peaks in the standard and in the test sample are projected onto the space that is orthogonal to the space spanned by the interferences. These projections are proportional (up to the noise) if data are trilinear. The proportionality is checked graphically from the first singular vector of the projected peaks, or from the plot of the orthogonal signal versus the net sensitivity. The use of these graphs is shown for simulated data and for the determination of 4-nitrophenol in river water samples with liquid chromatography/UV-Vis detection.