An improved method of isomolar series by dual-wavelength spectrophotometry

An improved method of isomolar series for determining the composition of an aqueous binary spectrophotometric system is proposed. It is based on the determination by dual-wavelength spectrophotometry of the equilibrium concentration of the chromogenic agent L added in excess, the absorbance of which has been found to be a linear function ofn/m, the composition index of the reaction product M _m L _n in the system, Hence it is a direct and reliable method, applicable also to systems in which the absorption spectra of L and M _m L _n overlap and can be resolved by instrumental masking.     

Simultaneous Determination of Atrazine and Chlorpyrifos in Pesticide Formulations,in Soils and Waters by Derivative Spectrophotometry and Ratio Spectra Derivative

Abstract

A new method is described to analyse a binary mixture of atrazine and chlorpyrifos, using first-derivative spectrophotometry for atrazine and first derivative of the ratio spectra for chlorpyrifos. The procedure does not require any separation step. Calibration graphs were linear up to 15 μg.mL^?1 of atrazine and to 10 μg.mL^?1 of chlorpyrifos. The method has been applied to determine both compounds in pesticide formulations, in soils and waters.     

<Emphasis Type="Italic">ABCD</Emphasis>-<Emphasis Type="Italic">Tool</Emphasis>, a software suite for the analysis of α/β spectra from liquid scintillation counting

This paper presents the alpha/beta complete deconvolution tool (ABCD-Tool), a C++ application for the analysis of spectra from liquid scintillation counting (LSC) measurements. In addition to the basic algorithms for standard gross alpha/beta analysis and the determination of the counting efficiency, the software implements a recent unfolding technique based on Fourier transforms, which gives precise and reliable results even in the case of complex, strongly overlapping spectra. The application is designed to be used with alpha/beta spectra generated from Perkin Elmer Wallac Quantulus 1220. However, future upgrades are scheduled in order to extend the compatibility to spectra from other LSC instruments in commerce.     

Generalized Gaussian reference curve measurement model for high‐performance liquid chromatography with diode array detector separation and its solution by multi‐target intermittent particle swarm optimization

In order to separate a high‐performance liquid chromatography with diode array detector (HPLC‐DAD) data set to chromatogram peaks and spectra for all compounds, a separation method based on the model of generalized Gaussian reference curve measurement (GGRCM) and the algorithm of multi‐target intermittent particle swarm optimization (MIPSO) is proposed in this paper. A parameter θ is constructed to generate a reference curve r(θ) for a chromatogram peak based on its physical principle. The GGRCM model is proposed to calculate the fitness ε(θ) for every θ, which indicates the possibility for the HPLC‐DAD data set to contain a chromatogram peak similar to the r(θ). The smaller the fitness is, the higher the possibility. The algorithm of MIPSO is then introduced to calculate the optimal parameters by minimizing the fitness mentioned earlier. Finally, chromatogram peaks are constructed based on these optimal parameters, and the spectra are calculated by an estimator. Through the simulations and experiments, the following conclusions are drawn: (i) the GGRCM‐MIPSO method can extract chromatogram peaks from simulation data set without knowing the number of the compounds in advance even when a severe overlap and white noise exist and (ii) the GGRCM‐MIPSO method can be applied to the real HPLC‐DAD data set. Copyright © 2014 John Wiley & Sons, Ltd.     

Precise determination of nonlinear function of ion mobility for explosives and drugs at high electric fields for microchip FAIMS

High‐field asymmetric waveform ion mobility spectrometry (FAIMS) separates ions by utilizing the characteristics of nonlinear ion mobility at high and low electric fields. Accurate ion discrimination depends on the precise solution of nonlinear relationships and is essential for accurate identification of ion species for applications. So far, all the nonlinear relationships of ion mobility obtained are based at low electric fields (E/N <65 Td). Microchip FAIMS (μ‐FAIMS) with small dimensions has high electric field up to E/N = 250 Td, making the approximation methods and conclusions for nonlinear relationships inappropriate for these systems. In this paper, we deduced nonlinear functions based on the first principle and a general model. Furthermore we considered the hydrodynamics of gas flow through microchannels. We then calculated the specific alpha coefficients for cocaine, morphine, HMX, TNT and RDX, respectively, based on their FAIMS spectra measured by μ‐FAIMS system at ultra‐high fields up to 250 Td. The results show that there is no difference in nonlinear alpha functions obtained by the approximation and new method at low field (<120 Td), but the error induced by using approximation method increases monotonically with the increase in field, and could be as much as 30% at a field of 250 Td. Copyright © 2015 John Wiley & Sons, Ltd.     

Automated Lipid A Structure Assignment from Hierarchical Tandem Mass Spectrometry Data

Infusion-based electrospray ionization (ESI) coupled to multiple-stage tandem mass spectrometry (MS ⁿ ) is a standard methodology for investigating lipid A structural diversity (Shaffer et al. J. Am. Soc. Mass. Spectrom. 18(6), 1080–1092, 2007). Annotation of these MS ⁿ spectra, however, has remained a manual, expert-driven process. In order to keep up with the data acquisition rates of modern instruments, we devised a computational method to annotate lipid A MS ⁿ spectra rapidly and automatically, which we refer to as hierarchical tandem mass spectrometry (HiTMS) algorithm. As a first-pass tool, HiTMS aids expert interpretation of lipid A MS ⁿ data by providing the analyst with a set of candidate structures that may then be confirmed or rejected. HiTMS deciphers the signature ions (e.g., A-, Y-, and Z-type ions) and neutral losses of MS ⁿ spectra using a species-specific library based on general prior structural knowledge of the given lipid A species under investigation. Candidates are selected by calculating the correlation between theoretical and acquired MS ⁿ spectra. At a false discovery rate of less than 0.01, HiTMS correctly assigned 85% of the structures in a library of 133 manually annotated Francisella tularensis subspecies novicida lipid A structures. Additionally, HiTMS correctly assigned 85% of the structures in a smaller library of lipid A species from Yersinia pestis demonstrating that it may be used across species.     

One-electron reduction of thionine studied by pulse radiolysis

One-electron reduction of thionine has been studied by using the technique of nanosecond pulse radiolysis and kinetic spectrophotometry. H,e _aq ⁻ as well as radicals derived from methanol, ethanol, isopropanol, THF, dioxane andt-butanol by H atom abstraction were used as reductants. The rate constants for the transfer of electrons from these radicalts to thionine were directly determined from the pseudo first-order formation rates of the product, semithionine and the one-electron reduction potential of thionine estimated. The absorption spectrum of semithionine in its different conjugate acid-base forms was found to be in agreement with previously reported spectra and the decay of the species was second order. By monitoring transient absorbance changes as a function of pH, twopK _a values were observed and, based on the effect of ionic strength on the second-order decay constants of the species were assigned to the equilibria described.     

Derivative spectrophotometric determination of holmium in rare earth mixtures with 2-(diphenylacetyl)indan-1,3-dione and octylphenyl poly(ethyleneglycol) ether

The zero-order and second-order derivative absorption spectra of the system of holmium with 2-(diphenylacetyl) indan-1, 3-dione and octylphenyl poly(ethyleneglycol) ether have been determined by derivative spectrophotometry. The molar absorptivity of absorption spectra and the derivative spectra are calculated respectively. The absorbances at the absorption maxima for the holmium complex are 48.5 (at 450 nm) and 14.5 (at 460 nm) times greater than for the corresponding chloride. The derivative spectra have been used to eliminate the interference of other lanthanides, and the sensitivity is again increased by a factor of about 5. The calibration graph is linear up to 25 g/ml of holmium. The detection limit, obtained from the sensitivity of the calibration graph and for 3S _b (S_b = standard deviation of a blank without holmium,n = 11), was 0.37 g/ml of holmium. The quantification limit (10S_b was 1.2 g/ml. The method has been applied successfully to synthetic and reference samples of rare earths.     

同步-偏振-导数荧光法同时测定三种苯二酚异构体的研究

苯二酚的三种异构体, 由于其吸收光谱和荧光光谱均重叠严重, 不能用常规分光光度法和荧光法进行同时测定. 而以λ＝0 nm进行同步扫描时, 在350～500 nm之间具有相似的荧光光谱特征, 其荧光强度有良好的加和性, 可以对三者进行总量测定. 研究还发现三种苯二酚异构体与Cu^2＋和异烟肼形成1∶1∶2的配位合物时, 用Δλ＝30 nm进行同步扫描并采用偏振和一阶导数法, 间苯二酚的导数荧光峰位于260 nm处, 对苯二酚的导数荧光峰位于320 nm处, 两者能很好分开, 而此时邻苯二酚荧光峰消失, 因此可在三者的混合物中分别测定间、对苯二酚, 然后再从总量中减去间、对苯二酚的含量, 从而测到邻苯二酚的浓度, 因此本工作通过上述方法可对三种苯二酚异构体进行同时测定. 其线性范围均在3×10^－6～5×10^－4 mol/L之内, 间苯二酚和对苯二酚的检出限分别是2.5×10^－7 mol/L和3.1×10^－7 mol/L; 其混和物总量的检出限是4.5×10^－7 mol/L, RSD均在5%以下. 该方法简便快速, 有良好的准确性和重复性, 用于环境水样中三种苯二酚的同时测定, 获得满意结果.     

Optimisation and validation of liquid chromatographic and partial least-squares-1 methods for simultaneous determination of enalapril maleate and nitrendipine in pharmaceutical preparations

Simultaneous determination of enalapril maleate (ENA) and nitrendipine (NIT) in pharmaceutical preparations was performed using liquid chromatography (LC) and the partial least-squares-1 (PLS-1) method. In LC, the separation was achieved on a C8 column and the optimum mobile phase for good separation in a gradient elution programme was found to be acetonitrile-water (φ _r = 81: 19) and optimum flow-rate, temperature, injection volume, and detection wavelength were set at 1.0 mL min⁻¹, 25°C, 10 μL, and 210 nm, respectively. Dienogest was selected as an internal standard. In the spectrophotometry, a PLS-1 chemometric method was used. The absorbance data matrix related to the concentration data matrix was established by measurement of absorbances in their zero order spectra with an increment of Δλ = 1 nm in the 220–290 nm range for ENA and with Δλ = 1 nm in the 230–290 nm range for NIT in the PLS-1 method. Following this step, calibration was established by using this data matrix to predict the unknown concentrations of ENA and NIT in their binary mixture. These optimised methods were validated and successfully applied to a pharmaceutical preparation in tablet form and the results were subjected to comparison.     

Recent development in derivative ultraviolet/visible absorption spectrophotometry: 2004-2008: A review

Several techniques have been proposed for treatment of spectrophotometric data, with the objective of extracting a largest amount of analytical information from spectra composed of unresolved bands. Undoubtedly, a major success was achieved by derivative treatment of the absorbance curves-plotting of the first or a higher order mathematical derivative of absorbance against wavelength (dA/dλ). Derivative spectrophotometry has been applied to many chemical systems, such as pharmaceuticals, foods, cosmetics, and environmental samples.The instrumental development and analytical applications of derivative UV-vis regions absorption spectrophotometry produced in the last 5 years (since 2004) are reviewed.     

Simultaneous spectrophotometric and liquid chromatographic determination of dextromethorphan hydrobromide,phenylephrine hydrochloride,and carbinoxamine maleate in pharmaceutical preparations

Simultaneous determination of dextromethorphan hydrobromide (DEX), phenylephrine hydrochloride (PHEN), and carbinoxamine maleate (CAR) in pharmaceutical preparations was performed by using liquid chromatograpy (LC) and spectrophotometry. In LC, the separation was achieved on a C18 column and the optimal mobile phase for satisfactory separation in a gradient elution program was found to be acetonitrile-sodium perchlorate solution (5: 95, v/v) initially, then a linear gradient up to 60% acetonitrile in 8 min. In spectrophotometric method, a chemometric technique, principal component regression (PCR), was used. In the method, the absorbance data matrix corresponding to the concentration data matrix was obtained by the measurement of absorbances in their zero order spectra by Δλ = 1 nm in the 210–300 nm range. Then, the calibration was obtained by using this data matrix for the prediction of unknown concentrations of DEX, PHEN, and CAR in their ternary mixture. The methods proposed were validated and successfully applied to a pharmaceutical preparation, capsule, and the results were compared.     

Determination of sulphamethizole in the presence of nitrofurantoine by derivative spectrophotometry and ratio spectra derivative

Two methods for determining sulphamethizol in the presence of nitrofurantoine in mixtures by first-derivative spectrophotometry and by the first derivative of the ratio spectra are described. The procedures do not require any separation step. In the first method the measurements are obtained in the zero-crossing wavelengths and the calibration graphs were linear up to 32 mug/ml of sulphamethizole at 251 and 278.5 nm. In the second method, the calibration graphs were linear up to 43 mug/ml by measuring at the maximum (263 nm), at the minimum (244 nm) and peak to peak. The methods were applied for determining sulphamethizole in a pharmaceutical product containing nitrofurantoine.     

Contacted Ion Pairs in Aqueous CuCl2 by the Combination of Ratio Spectra,Difference Spectra,Second Order Difference Spectra in the UV-Visible Spectra

The microstructure of aqueous CuCl₂ has been studied through lots of technologies for many years; however, it remains a controversial subject. In this study, a new spectroscopic method has been proposed to analyze the UV-visible spectra of thin film of CuCl₂/H₂O solutions at different concentrations. This method is the combination of ratio spectra, difference spectra and second order difference spectra. By using this method, two new bands at ~230 and ~380 nm are obviously observed. The bands are assigned as the contacted ion pairs[CuCl₃(H₂O)_n]^- or[CuCl₄(H₂O)_n]^2-, which demonstrates that ion pairs exist in the CuCl₂/H₂O solution. Such finding agrees with the recent theoretical spectra obtained by time-dependent density functional theory. Furthermore, the populations of the contacted ion pairs are discussed. This study not only offers the direct spectroscopic evidence of[CuCl₃(H₂O)_n]^- or[CuCl₄(H₂O)_n]^2- in aqueous CuCl₂, but also suggests that the spectroscopic analysis method is powerful to extract the weak bands in a strong overlapping spectrum.     

Mixed IR/Vis Two‐Dimensional Spectroscopy: Chemical Exchange beyond the Vibrational Lifetime and Sub‐ensemble Selective Photochemistry

Two‐dimensional exchange spectroscopy (2D EXSY) is a powerful method to study the interconversion (chemical exchange) of molecular species in equilibrium. This method has recently been realized in femtosecond 2D‐IR spectroscopy, dramatically increasing the time resolution. However, current implementations allow the EXSY signal (and therefore the chemical process of interest) only to be tracked during the lifetime (T₁) of the observed spectroscopic transition. This is a severe limitation, as typical vibrational T₁ are only a few ps. An IR/Vis pulse sequence is presented that overcomes this limit and makes the EXSY signal independent of T₁. The same pulse sequence allows to collect time‐resolved IR spectra after electronic excitation of a particular chemical species in a mixture of species with strongly overlapping UV/Vis spectra. Different photoreaction pathways and dynamics of coexisting isomers or of species involved in different intermolecular interactions can thus be revealed, even if the species cannot be isolated because they are in rapid equilibrium.     

Highly sensitive ion preconcentration method based on flow sorbent extraction using multiwall carbon nanotubes

In this work a solid phase on-line uranium ion preconcentration system coupled with spectrophotometry has been developed. The method is based on uranyl ion preconcentration at pH 3.75 onto multiwall carbon nanotubes treated with HNO₃. After preconcentration, the uranyl ions are eluted with 0.32?mol?L^?1HCl followed by reaction with 3,6-bis[(2-arsonophenyl)-azo]-4,5-dihydroxy-2,7-naphthalendisulfonic acid 0.08%[w/v] (Arsenazo III), which had maximum monitored absorbance of 650?nm. Effects of the pertinent experimental parameters on the system were investigated by means of 2^6?2 fractional factorial design, while optimization was carried out using the Doehlert matrix. Under optimized conditions, detection and quantification limits were found to be 0.21 and 0.7?µg?L^?1, respectively. The analytical curve ranged from 5 to 150?µg?L^?1 (r?=?0.998), while the relative standard deviations (RSD) were 3.27 and 2.56% for the respective uranium concentrations of 10 and 100?µg?L^?1 (n?=?10). The features obtained for the on-line preconcentration system were: preconcentration factor of 228, concentration efficiency of 57?min^?1, consumption index of 0.13?mL and sample throughput of 15?h^?1. In order to assess the accuracy of the proposed method, addition and recovery studies were carried out on spring water samples from different sources and synthetic seawater with satisfactory results ranging from 94.85 up to 103.65%.     

Spectrophotometric Methods for the Determination of Acediasulfone in Mixture with Cinchocaine

Abstract

Derivative spectrophotometry techniques (ratio‐spectra first derivative and zero‐crossing first derivative) were described for simultaneous determination of acediasulfone and cinchocaine. Acediasulfone was also determined via the formation of a colored product as a result of its reaction with p‐dimethylaminobenzaldehyde. In the ratio‐spectra first derivative method, the measurements were taken at 310 and 233.9 nm for acediasulfone and cinchocaine, respectively. By the zero‐crossing first derivative method, lines of regression were taken at 318 and 233 nm for acediasulfone and cinchocaine, respectively. In the colorimetric method, absorbance measurements were obtained at 452 nm. Acediasulfone showed linearity over concentration ranges 2–14 µg/ml, 2–16 µg/ml, and 12–60 µg/ml for ratio‐spectra first derivative, zero‐crossing first derivative, and colorimetric methods, whereas cinchocaine showed linearity over concentration ranges 1–10 µg/ml and 2.28–16 µg/ml for ratio‐spectra first derivative and zero‐crossing first derivative techniques. The proposed methods proved to be specific and accurate for the analysis of the cited drugs in laboratory‐prepared mixtures and dosage form. The obtained results agree statistically with those obtained by reference methods.     

A new compound of uranium VI with formamide UO3 · HCONH2 · 0.5H2O

A new compound of uranium VI has been prepared by thermolysis of uranyl formate diammoniate in an ammonia environment. Chemical analysis and infrared spectrophotometry favor the formula UO₃ · HCONH · 0.5H₂O. X-Ray analysis is in agreement with an orthorhombic lattice having parameters a = 6.88 Å, b = 23.46 Å, c = 24.67 Å. The photoluminescence spectra of this compound are presented.     

Cost and sensitivity of restricted active‐space calculations of metal L‐edge X‐ray absorption spectra

The restricted active‐space (RAS) approach can accurately simulate metal L‐edge X‐ray absorption spectra of first‐row transition metal complexes without the use of any fitting parameters. These characteristics provide a unique capability to identify unknown chemical species and to analyze their electronic structure. To find the best balance between cost and accuracy, the sensitivity of the simulated spectra with respect to the method variables has been tested for two models, [FeCl₆]^3– and [Fe(CN)₆]^3–. For these systems, the reference calculations give deviations, when compared with experiment, of ≤1 eV in peak positions, ≤30% for the relative intensity of major peaks, and ≤50% for minor peaks. When compared with these deviations, the simulated spectra are sensitive to the number of final states, the inclusion of dynamical correlation, and the ionization potential electron affinity shift, in addition to the selection of the active space. The spectra are less sensitive to the quality of the basis set and even a double‐ζ basis gives reasonable results. The inclusion of dynamical correlation through second‐order perturbation theory can be done efficiently using the state‐specific formalism without correlating the core orbitals. Although these observations are not directly transferable to other systems, they can, together with a cost analysis, aid in the design of RAS models and help to extend the use of this powerful approach to a wider range of transition metal systems. © 2015 Wiley Periodicals, Inc.