Local resolution of two-way data from multicomponent equilibria

A self-modeling curve resolution (SMCR) method is proposed to calculate concentration and spectral profiles for the two-way spectral data from an equilibrium containing several chemical components. The proposed method has three main distinctive steps: (i) fixed size moving window evolving factor analysis (FSMWEFA) is used to identify the selective and zero concentration regions for a desired component, (ii) orthogonal projection resolution (OPR) is used to calculate its concentration profile and (iii) the component striping is done directly to resolve other components. The results of simulated and real polyprotic acid dissociation equilibria showed that the proposed combined method performs well even in situation when the successive stepwise equilibrium constants are close to each other. The applicability of method for resolving the triprotic acid system with rank deficiency due full spectral overlapping of two involved chemical species also is shown.     

Spectrophotometric study of complexation equilibria with H-point standard addition and H-point curve isolation methods

The use of H-point curve isolation (HPCIM) and H-point standard addition methods (HPSAM) for spectrophotometric studies of complex formation equilibria are proposed. One step complex formation, two successive stepwise and mononuclear complex formation systems, and competitive complexation systems are studied successfully by the proposed methods. HPCIM is used for extracting the spectrum of complex or sum of complex species and HPSAM is used for calculation of equilibrium concentrations of ligand for each sample. The outputs of these procedures are complete concentration profiles of equilibrium system, spectral profile of intermediate components, and good estimation of conditional formation constants. The reliability of the method is evaluated using model data. Spectrophotometric studies of murexide-calcium, dithizone-nickel, methyl thymol blue (MTB)-copper, and competition of murexide and sulfate ions for complexation with zinc, are used as experimental model systems with different complexation stoichiometries and spectral overlapping of involved components.     

断层扫描分析法用于联用色谱二维数据的解析Ⅱ. 定量分析:原理与应用

提出了一种全新的色谱一光谱二维数据信息处理手段——断层扫描分析法。本研究介绍断层扫描分析法的定量分析原理：在重叠色谱峰簇中,每个色谱保留时间处都可得到一条光谱“断层”;针对不同的光谱“断层”,可结合褶合曲线分析法进行定量分析,并最终获得重叠色谱峰簇中待测组分的定量信息。用断层扫描分析法对一实验体系进行了定量分析,结果满意。     

Application of modern chemometric methods to the study of equilibria in solutions

The possibility of the spectrometric-chemometric study of equilibria in solutions is demonstrated for substances with strongly overlapping spectra, in particular, using the independent component analysis (MILCA and SIMPLISMA algorithms) and the alternating least squares algorithm (MCR-ALS). Using the chemometric approach allows one to resolve spectral curves, identify species present in the solution, and calculate the characteristics of equilibria. The proposed approach is illustrated on a series of examples (study of a tautomeric equilibrium and complexation reactions).     

Fast Determination of Phenanthrene in Soil by Gas Chromatography-Mass Spectrometry Using Chemometric Resolution and Standard Addition Method

A method for fast determination of the component in complex samples by using gas chromatography‐mass spectrometry (GC‐MS) was developed and used for quantitative analysis of phenanthrene in soils. In the method, window independent component analysis (WICA) was used for resolving the mass spectrum and non‐negative immune algorithm (NNIA) was employed for obtaining the chromatographic profile. Therefore, spectral and chromatographic information of a specific component can be obtained from the measured GC‐MS data of overlapping and high background. Six soil samples collected from different places were analyzed. The tedious pretreatments in preparing the samples and the elution in the separation were simplified for speeding up the analysis. Due to the complexity of the matrix, standard addition method was adopted for the final quantification. The applicability of the method was validated with a spiked sample and the results of the six samples are reasonable.     

Rank annihilation factor analysis for spectrophotometric study of complex formation equilibria

The use rank annihilation factor analysis (RAFA) for spectrophotometric studies of complex formation equilibria are proposed. One-step complex formation and two successive and mononuclear complex formation systems studied successfully by proposed methods. When the complex stability constant acts as an optimizing object, and simply combined with the pure spectrum of ligand, the rank of original data matrix can be reduced by one by annihilating the information of the ligand from the original data matrix. The residual standard deviation (R.S.D.) of the residual matrix after bilinearization of the background matrix is regarded as the evaluation function. The performance of the method has been evaluated by using synthetic data. For two-step successive complex formation systems, the effects of noise level and equilibrium constants K₁ and K₂ on output of algorithm are investigated. The applicability of method for resolving the two-step successive complex formation systems with full spectral overlapping of two complex species also is shown. Spectrophotometric studies of murexide-calcium, dithiazone-nickel and methyl thymol blue (MTB)-copper are used as experimental model systems with different complexation stoichiometries and spectral overlapping of involved components.     

Weighted two-band target entropy minimization for the reconstruction of pure component mass spectra: Simulation studies and the application to real systems

A method is proposed, on the basis of a recently developed algorithm--Band Target Entropy Minimization (BTEM)--to reconstruct mass spectra of pure components from mixture spectra. This method is particular useful in dealing with spectral data with discrete features (like mass spectra). Compared to the original BTEM, which has been applied to differentiable spectroscopies such as Fourier-transfer infrared spectroscopy (FTIR), ultraviolet (UV), Raman, and nuclear magnetic resonance (NMR), the latest modifications were obtained through: (1) Reformulating the objective function using the peak heights instead of their derivatives; (2) weighting the abstract vector VT to reduce the effect of noise; (3) using a two-peak targeting strategy (tBTEM) to deal with strongly overlapping peaks; and (4) using exhaustive search to locate all the component spectra. A set of 50 multi-component mass spectra was generated from ten reference experimental pure component spectra. Many of the compounds chosen have common MS fragments and therefore, many of the pure component spectra have considerable intensity in same data channels. In addition, a set of MS spectra from a real system with four components was used to examine the newly developed algorithm. Successful reconstruction of the ten component spectra of the simulated system and the four component spectra of the real system was rapidly achieved using the new tBTEM algorithm. The advantages of the new algorithm and its implication for rapid system identification of unknown mixtures are readily apparent.     

A simple method to extract spectral parameters using fractional derivative spectrometry

The nonlinear fitting method, based on the ordinary least squares approach, is one of several methods that have been applied to fit experimental data into well-known profiles and to estimate their spectral parameters. Besides linearization measurement errors, the main drawback of this approach is the high variance of the spectral parameters to be estimated. This is due to the overlapping of individual components, which leads to ambiguous fitting. In this paper, we propose a simple mathematical tool in terms of a fractional derivative (FD) to determine the overlapping band spectral parameters. This is possible because of several positive effects of FD connected with the behavior of its zero-crossing and maximal amplitude. For acquiring a stable and unbiased FD estimate, we utilize the statistical regularization method and the regularized iterative algorithm when a priori constraints on a sought derivative are available. Along with the well-known distributions such as Lorentzian, Gaussian and their linear combinations, the Tsallis distribution is used as a model to correctly assign overlapping bands. To demonstrate the power of the method, we estimate unresolved band spectral parameters of synthetic and experimental infra-red spectra.     

Pure component spectral reconstruction from mixture data using SVD, global entropy minimization, and simulated annealing. Numerical investigations of admissible objective functions using a synthetic 7-species data set

A combination of singular value decomposition, entropy minimization, and simulated annealing was applied to a synthetic 7-species spectroscopic data set with added white noise. The pure spectra were highly overlapping. Global minima for selected objective functions were obtained for the transformation of the first seven right singular vectors. Simple Shannon type entropy functions were used in the objective functions and realistic physical constraints were imposed in the penalties. It was found that good first approximations for the pure component spectra could be obtained without the use of any a priori information. The present method out performed the two widely used routines, namely Simplisma and OPA-ALS, as well as IPCA. These results indicate that a combination of SVD, entropy minimization, and simulated annealing is a potentially powerful tool for spectral reconstructions from large real experimental systems.     

A two-dimensional (magnetic field and concentration) electron paramagnetic resonance method for analysis of multispecies complex equilibrium systems. information content of EPR spectra

A two-dimensional simulation method has been developed for the interpretation of electron paramagnetic resonance (EPR) spectra consisting of a multitude of strongly overlapping signal components. The set of EPR spectra for complex equilibrium systems is analyzed simultaneously as a function of metal and ligand concentrations and pH. The formation constants of the various species are adjusted together with the magnetic parameters of the component EPR spectra. At most 10 EPR-active and 5 EPR-silent species can be involved to simulate a maximum of 36 experimental spectra, while the number of adjusted parameters is at most 100. Statistical parameters are suggested to give the confidence intervals for parameter estimation and to distinguish alternative speciation models. The efficiency of the program is demonstrated for the copper(II)--L-asparagine system, in which 10 species, including 3 pairs of isomers, are characterized with magnetic parameters and formation constants. On the basis of the magnetic parameters, a structural assignment is made for the detected species. The two-dimensional approach can also supply the formation constant of the EPR-silent species, as demonstrated for the copper(II)--glycyl-L-serine system.     

正交投影用于一维重叠色谱峰分辨及背景扣除

对于两组份色谱重叠峰体系,当以小组份色谱峰作为干扰时,本文利用正交投影方法,通过构造正交投影矩阵,利用原始信号及其投影与背景之间的内在关系来确定真实背景,从而将背景干扰予以扣除,使含背景干扰的一维重叠色谱峰得以分辨。模拟研究表明,对于两组份色谱峰重叠体系当以小色谱峰为干扰时本文方法具有很好的分辨效果,对于完全重叠峰,即使其峰分离度为零能得到满意的结果。     

联用色谱数据的双窗口因子分析

利用组分光谱的特征信息,发展了一种能直接对联用色谱重叠峰中组分进行定性定量分析的新方法──双窗口因子分析（dualwindowfactoranalysis,DWPA）。该法可从多组分重叠峰中定性目标组分,且在未经其它组分的分辨下可直接对目标组分的光谱、色谱进行分辨。因此更适应于联用色谱对复杂体系中待测组分的定性定量分析。用该法成功地对4组分重叠峰进行了分析,实验结果令人满意。     

Component recognition with three‐dimensional fluorescence spectra based on non‐negative matrix factorization

Non‐negative matrix factorization (NMF) is a widely used approach in signal processing. In this work, we apply it to the component recognition of mixtures with multicomponent three‐dimensional fluorescence spectra. Compared with the popular PARAFAC for component recognition, NMF has the following advantages: on one hand, the decomposed spectra are three dimensional, and thus, more information can be obtained, which is beneficial for component recognition; on the other hand, the decomposed spectra are non‐negative and thus have a certain physical significance. More importantly, we propose a type of integrated similarity indices for the three‐dimensional fluorescence spectra, which, by construction, is good at component recognition from overlapping fluorescence spectra. Experiment results demonstrate that NMF combined with integrated similarity index provides an effective method for component recognition of multicomponent three‐dimensional overlapping fluorescence spectra. Copyright © 2011 John Wiley & Sons, Ltd.     

Aggregation of 2‐Aminobenzimidazole—A Combined Experimental and Theoretical Investigation

An investigation of 2‐aminobenzimidazole was carried out by calculations at HF, MP2, and DFT levels of theory and also by UV and IR spectroscopy. The quantum chemical calculations predict a full shift of the equilibrium towards the amino form, but the absorption spectra in different solvents distinctly show a two‐component equilibrium system. Examination of possible equilibria in solution shows that an equilibrium between two dimeric forms of the amino tautomer of 2‐aminobenzimidazole explains the spectral observations.     

Li2SO4-EtOH-H2O体系25℃气-液-固平衡和液相物理化学性质的研究

研究Li_2SO_4-EtOH-H_2O体系25 ℃气液平衡及液相的粘度和密度。湿渣法确定平衡固相在整个浓度范围内均为Li_2SO_4·H_2O。用经验公式ln(y/y_0)=K_1x+K_2x~2+K_2x~3对体系的溶解度和密度数据进行关联。硫酸锂加入到液相后由于盐离子静电作用对乙醇-水体系粘度的影响。按Jaques的假二元体系模型, 用WILSON, NRTL方程关联气液平衡数据。     

Modified indirect hard modeling for non-invasive Raman measurements containing surface interference

Non-invasive Raman spectroscopy has been used in an increasing number of applications in recent years. However, in situations where surface signal is excessive, the acquired spectrum of probed sample suffers from surface interference in either conventional backscattering Raman or specially designed Raman methods. A computational method for Raman spectral recovery is required. Strong overlapping of Raman bands and intense fluorescence are the main obstacles that hinder the spectral recovery. In this paper, we present a modified version of an indirect hard modeling algorithm to extract the true Raman spectrum of the probed sample in a two-layer system. The proposed algorithm requires two spectra. By an iterative stepwise optimization, it models one spectrum as a combination of a scaling of the other spectrum, a polynomial baseline and the Raman peaks of the probed sample. It addresses the issue of Raman bands overlapping as well as intense fluorescence interference. The performance of the algorithm is evaluated on experimental Raman spectra. Comparative studies show that the proposed algorithm provides better results for Raman spectral recovery.     

Simultaneous observation of reagent consumption and product formation with the kinetics of benzaldehyde and aniline reaction in FTIR liquid cell

Monitoring of a reaction in FTIR liquid cell has complex spectral futures due to the presence of solvent, unreacted reagents; acid catalysis and other additives. The current work was performed to study the kinetics of the reaction between benzaldehyde and aniline by simultaneous time dependent observation in FTIR liquid cell.Since the FTIR liquid cell used in this work was a closed system, background defining method allowed us to observe the changes in the concentration of each component in the liquid cell at different side of absorbance or transmittance axes. The changes in concentration arising from the reaction provide both the spectra and amount of the product and reagent, independently without having to isolate them from the reaction mixture. Therefore, it would be possible to follow the amount of decreases in concentration of the reagent and conversely, increases in concentration of the product. Consequently, using this method the reaction of benzaldehyde and aniline was found to go to equilibrium in chloroform.     

Shotgun sequencing small oligonucleotides by nozzle-skimmer dissociation and electrospray ionization mass spectrometry

Nozzle-skimmer dissociation in combination with de novo sequencing was investigated as an approach for increasing the throughput of oligonucleotide analysis attainable by electrospray ionization mass spectrometry. An experimental method allowing for the sequential generation of precursor and fragment ion data during direct infusion of sample was developed. These data can then be used with readily available de novo sequencing software to characterize small oligonucleotides. When this approach was applied to mixtures of oligonucleotides, it was found that de novo sequencing becomes limited due to spectral congestion and overlapping oligonucleotide m/z dissociation product values. Self-packed C(18) microspray emitters were investigated as a means of reducing spectral complexity. It was found that such emitters allow for the analysis of oligonucleotide mixtures with minimal component overlap, and these emitters provide additional benefits of pre- concentrating and desalting the sample. These developments can provide a route for the more rapid characterization of ribonucleic acid endonuclease digestion mixtures.     

直观推导式演进特征投影法对环境样本中多环芳烃的定性定量分析

基于新近发展的直观推导式演进特征投影法(HELP), 本文提出了一个对二维数据进行同时定性定量的分析方法, 并将其成功地用于环境样本中多环芳烃化合物定量解析。对于一维色谱难以定量的重叠峰, HELP方法充分利用色谱、光谱两方面的选择性信息, 得到了具有真实物理意义的唯一解。在定性分辨结果的基础上, 本文还提出了三种可能的定量方法。这种二维数据的解析新方法, 能大幅度地降低对色谱分离条件的要求, 可直接用于复杂实际样本的定性定量分析。     

UV-Vis spectroscopic and chemometric study on the aggregation of ionic dyes in water

The monomer-dimer equilibrium in several ionic dyes (Methylene Blue, Acridine Orange, Nile Blue A, Neutral Red, Rhodamine 6G and Safranine O) has been investigated by means of UV-Vis spectroscopy. The data have been processed by a recently developed method for quantitative analysis of undefined mixtures, based on simultaneous resolution of the overlapping bands in the whole set of absorption spectra. In the cases of Acridine Orange a second chemometric approach has been used as a reference. It is based on a decomposition of the recorded spectra into a product of target and projection matrices using non iterative partial least squares (NIPALS). The matrices are then rotated to give the correct concentrations, spectral profiles of the components and the equilibrium constant. The dimeric constants determined by the two methods were in excellent agreement, evidencing the accuracy of the analysis. From the calculated dimeric constant and monomer and dimer spectra, the structures of the dimeric forms of the studied dyes are estimated.