A comparative study of IC,ICP-AES,and NAA measurements on chlorine,bromine, and sodium in natural waters

A suite of shallow and deep subsurface waters from southwestern Illinois has been analyzed for chlorine (CT), bromine (Br^?), and sodium (Na⁺) using three different methods. Cl and Br were analyzed by ion chromatography (IC) and neutron activation analysis (NAA). Na was analyzed using inductively coupled plasma-atomic emission spectrometry (ICP-AESS) and NAA. In addition, five water standards were prepared with compositions over the range of Cl, Br, and Na concentrations in the natural waters were analyzed using the same methods. Analytical results for the prepared standards by the different methods were in good agreement. However, analytical results on natural waters yielded generally poor agreement between the methods. Our results suggest that solute concentrations and ratios between major solutes in subsurface waters determined by IC and ICP-AES may involve substantial laboratory error.     

A comparison of ten different methods for the analysis of saturates, olefins, benzene, total aromatics, and oxygenates in finished gasolines

The Technical Committee 19 of the European Committee for Standardization (CEN/TC19) in the "Lisbon resolution" requested to evaluate replacement methods to the fluorescent indicator absorption (FIA) (American Standardization for Testing and Material D 1319) method for the determination of aromatics and olefins in gasolines. In the same resolution it was requested to review the two existing methods for the determination of benzene content of gasolines, anticipating lower limit values in future European gasoline specifications. As a result of this request, a round robin (RR) was organized in which 8 gasoline samples are analyzed using 10 different methods in 33 laboratories. The methods used in the RR include, apart from the FIA method, one-dimensional gas chromatography (GC) and multidimensional GC, with and without specific detectors and spectroscopic analysis methods. This study describes these methods in short, gives an evaluation of the results of the RR, and draws a conclusion on the outcome.     

Computational prediction of metabolism: sites, products, SAR, P450 enzyme dynamics, and mechanisms

Metabolism of xenobiotics remains a central challenge for the discovery and development of drugs, cosmetics, nutritional supplements, and agrochemicals. Metabolic transformations are frequently related to the incidence of toxic effects that may result from the emergence of reactive species, the systemic accumulation of metabolites, or by induction of metabolic pathways. Experimental investigation of the metabolism of small organic molecules is particularly resource demanding; hence, computational methods are of considerable interest to complement experimental approaches. This review provides a broad overview of structure- and ligand-based computational methods for the prediction of xenobiotic metabolism. Current computational approaches to address xenobiotic metabolism are discussed from three major perspectives: (i) prediction of sites of metabolism (SOMs), (ii) elucidation of potential metabolites and their chemical structures, and (iii) prediction of direct and indirect effects of xenobiotics on metabolizing enzymes, where the focus is on the cytochrome P450 (CYP) superfamily of enzymes, the cardinal xenobiotics metabolizing enzymes. For each of these domains, a variety of approaches and their applications are systematically reviewed, including expert systems, data mining approaches, quantitative structure-activity relationships (QSARs), and machine learning-based methods, pharmacophore-based algorithms, shape-focused techniques, molecular interaction fields (MIFs), reactivity-focused techniques, protein-ligand docking, molecular dynamics (MD) simulations, and combinations of methods. Predictive metabolism is a developing area, and there is still enormous potential for improvement. However, it is clear that the combination of rapidly increasing amounts of available ligand- and structure-related experimental data (in particular, quantitative data) with novel and diverse simulation and modeling approaches is accelerating the development of effective tools for prediction of in vivo metabolism, which is reflected by the diverse and comprehensive data sources and methods for metabolism prediction reviewed here. This review attempts to survey the range and scope of computational methods applied to metabolism prediction and also to compare and contrast their applicability and performance.     

Development and validation of two LC-MS/MS methods for the detection and quantification of amphetamines, designer amphetamines, benzoylecgonine, benzodiazepines, opiates, and opioids in urine using turbulent flow chromatography

In the context of driving ability diagnostics in Germany, administrative cutoffs for various drugs and pharmaceuticals in urine have been established. Two liquid chromatography–tandem mass spectrometry methods for simultaneous detection and quantification of amphetamines, designer amphetamines, benzoylecgonine, benzodiazepines, opiates, and opioids in urine were developed and validated. A 500-μL aliquot of urine was diluted and fortified with an internal standard solution. After enzymatic cleavage, online extraction was performed by an ion-exchange/reversed-phase turbulent flow column. Separation was achieved by using a reversed-phase column and gradient elution. For detection, a Thermo Fisher TSQ Quantum Ultra Accurate Mass tandem mass spectrometer with positive electrospray ionization was used, and the analytes were measured in multiple-reaction monitoring mode detecting two transitions per precursor ion. The total run time for both methods was about 15 min. Validation was performed according to the guidelines of the Society of Toxicological and Forensic Chemistry. The results of matrix effect determination were between 78 % and 116 %. The limits of detection and quantification for all drugs, except zopiclone, were less than10?ng/mL and less than 25 ng/mL, respectively. Calibration curves ranged from 25 to 200 ng/mL for amphetamines, designer amphetamines, and benzoylecgonine, from 25 to 250 ng/mL for benzodiazepines, from 12.5 to 100 ng/mL for morphine, codeine, and dihydrocodeine, and from 5 to 50 ng/mL for buprenorphine and norbuprenorphine. Intraday and interday precision values were lower than 15 %, and bias values within?±?15 % were achieved. Turbulent flow chromatography needs no laborious sample preparation, so the workup is less time-consuming compared with gas chromatography–mass spectrometry methods. The methods are suitable for quantification of multiple analytes at the cutoff concentrations required for driving ability diagnostics in Germany.     

Photochemistry of N-acetyl-, N-trifluoroacetyl-, N- mesyl-, and N-tosyldibenzothiophene sulfilimines

Time-resolved infrared (TRIR) spectroscopy, product studies, and computational methods were applied to the photolysis of sulfilimines derived from dibenzothiophene that were expected to release acetylnitrene, trifluoroacetylnitrene, mesylnitrene, and tosylnitrene. All three methods provided results for acetylnitrene consistent with literature precedent and analogous experiments with the benzoylnitrene precursor, i.e., that the ground-state multiplicity is singlet. In contrast, product studies clearly indicate triplet reactivity for trifluoroacetylnitrene, though TRIR experiments were more ambiguous. Product studies suggest that these sulfilimines are superior sources for sulfonylnitrenes, which have triplet grounds states, to the corresponding azides, and computational studies shed light on the electronic structure of the nitrenes.     

Speciation of beryllium, nickel, and vanadium in soil samples from Csepel Island, Hungary

Sequential leaching methods have been used for the speciation of Be, Ni, and V in five soil samples from Csepel Island on the Danube river located near an oil-fired power plant. The concentrations of the elements of the extracts were determined by inductively coupled plasma mass spectrometry. The total efficiency (the sum of the extracted metals divided by metal fraction which is soluble in aqua regia) of the five-step method was always higher. The difference for Ni was considerable, because of the high abundance of Ni found in the moderately reducible fraction, which is absent from the three-step method. The sum of the mobile species (exchangeable, carbonatic, and easily reducible) determined by both methods, were in reasonable agreement; this was not so for the individual fractions. There were greater differences between the non-mobile fractions (moderately reducible and oxidizable), because of the presence or absence of the moderately reducible fraction. For both methods there was good correlation between the oxidizable fraction and the organic matter content of the soils.     

Speciation of beryllium, nickel, and vanadium in soil samples from Csepel Island, Hungary

Sequential leaching methods have been used for the speciation of Be, Ni, and V in five soil samples from Csepel Island on the Danube river located near an oil-fired power plant. The concentrations of the elements of the extracts were determined by inductively coupled plasma mass spectrometry. The total efficiency (the sum of the extracted metals divided by metal fraction which is soluble in aqua regia) of the five-step method was always higher. The difference for Ni was considerable, because of the high abundance of Ni found in the moderately reducible fraction, which is absent from the three-step method. The sum of the mobile species (exchangeable, carbonatic, and easily reducible) determined by both methods, were in reasonable agreement; this was not so for the individual fractions. There were greater differences between the non-mobile fractions (moderately reducible and oxidizable), because of the presence or absence of the moderately reducible fraction. For both methods there was good correlation between the oxidizable fraction and the organic matter content of the soils.     

Comparison of liquid-liquid extraction, solid-phase extraction and co-precipitation preconcentration methods for the determination of cadmium, copper, nickel, lead and zinc in seawater

Three major types of pre-concentration methods were evaluated and optimised for the extraction and determination of Cd, Cu, Ni, Pb and Zn from seawater samples. The traditional APDC/DDDC-Freon liquid-liquid extraction method showed excellent results for a multi-elemental analysis. However, the technique is labour consuming, very sensitive to operational conditions, employs environmentally unsafe and expensive solvents and requires large sample volumes. In the solid phase extraction method, the performances of a traditional Amberlite XAD-4 and a novel Dowex Optipore V-493 were evaluated. Application of Dowex Optipore V-493 resin provided better results at low concentrations than the generally used Amberlite XAD-4 resin using low sample volumes. However, the presence of natural organic compounds may decrease extraction efficiency of both resins for Cu. Thus, a pre-treatment with UV irradiation is advantageous for samples with high organic content. Cobalt co-precipitation methods showed good Cu and Ni recoveries, but gave poor results for Cd at low concentrations. In addition, high sample volumes are required. Both solid phase and co-precipitation methods showed unsatisfactory results in determination of Pb. Finally, a summary of methods advantages are given for choosing the most suitable method.     

Brownian Dynamics, Molecular Dynamics, and Monte Carlo modeling of colloidal systems

This paper serves as an introductory review of Brownian Dynamics (BD), Molecular Dynamics (MD), and Monte Carlo (MC) modeling techniques. These three simulation methods have proven to be exceptional investigative solutions for probing discrete molecular, ionic, and colloidal motions at their basic microscopic levels. The review offers a general study of the classical theories and algorithms that are foundational to Brownian Dynamics, Molecular Dynamics, and Monte Carlo simulations. Important topics of interest include fundamental theories that govern Brownian motion, the Langevin equation, the Verlet algorithm, and the Metropolis method. Brownian Dynamics demonstrates advantages over Molecular Dynamics as pertaining to the issue of time-scale separation. Monte Carlo methods exhibit strengths in terms of ease of implementation. Hybrid techniques that combine these methods and draw from these efficacies are also presented. With their rigorous microscopic approach, Brownian Dynamics, Molecular Dynamics, and Monte Carlo methods prove to be especially viable modeling methods for problems with challenging complexities such as high-level particle concentration and multiple particle interactions. These methods hold promising potential for effective modeling of transport in colloidal systems.     

Comparison of topological, shape, and docking methods in virtual screening

Virtual screening benchmarking studies were carried out on 11 targets to evaluate the performance of three commonly used approaches: 2D ligand similarity (Daylight, TOPOSIM), 3D ligand similarity (SQW, ROCS), and protein structure-based docking (FLOG, FRED, Glide). Active and decoy compound sets were assembled from both the MDDR and the Merck compound databases. Averaged over multiple targets, ligand-based methods outperformed docking algorithms. This was true for 3D ligand-based methods only when chemical typing was included. Using mean enrichment factor as a performance metric, Glide appears to be the best docking method among the three with FRED a close second. Results for all virtual screening methods are database dependent and can vary greatly for particular targets.     

Development and validation of spectrophotometric methods for determination of fluoxetine, sertraline, and paroxetine in pharmaceutical dosage forms

Three simple and sensitive spectrophotometric methods were developed and validated for determination of the hydrochloride salts of fluoxetine, sertraline, and paroxetine in their pharmaceutical dosage forms. These methods were based on the reaction of the N-alkylvinylamine formed from the interaction of the free secondary amino group in the investigated drugs and acetaldehyde with each of 3 haloquinones, i.e., chloranil, bromanil, and 2,3-dichloronaphthoquinone, to give colored vinylamino-substituted quinones. The colored products obtained with chloranil, bromanil, and 2,3-dichloronaphthoquinone exhibit absorption maxima at 665, 655, and 580 nm, respectively. The factors affecting the reactions were studied and optimized. Under the optimum reaction conditions, linear relationships with good correlation coefficients (0.9986-0.9999) were found between the absorbances and the concentrations of the investigated drugs in the range of 4-120 microg/mL. The limits of detection for the assays ranged from 1.19 to 2.98 microg/mL. The precision values of the methods were satisfactory; the relative standard deviations were 0.56-1.24%. The proposed methods were successfully applied to the determination of the 3 drugs in pure and pharmaceutical dosage forms with good accuracy; the recoveries ranged from 99.1 to 101.3% with standard deviations of 1.15-1.92%. The results compared favorably with those of reported methods.     

Methods of extraction,preconcentration, and determination of quercetin

State-of-the-art methods of the extraction, preconcentration, and determination of quercetin and other flavonoids are described. Different methods of sample preparation of real samples are compared, including solvent extraction from solid matrices and liquid-liquid, supercritical fluid, and solid-phase extraction. The following main determination methods are discussed: HPLC, thin-layer chromatography, capillary electrophoresis, spectrophotometry, luminescence, and electrochemical methods. Some examples of quercetin determination in biological fluids, food products, biologically active food supplements, pharmaceutical preparations, and plant samples are given.     

Quantum chemical study of the tautomerism, geometry, and electronic structure of 1,2,3- and 1,2,4-triazoles

A systematic study was carried out on the tautomerism and geometry of 1,2,3- and 1,2,4-triazoles using the semiempirical AM1, PM3, MNDO, and MINDO/3 methods and nonempirical quantum chemical methods taking account of electronic correlation (MP2). The semiempirical methods were found to give incorrect results for the tautomerism of these triazoles, while the nonempirical methods correctly give the energy relationships and show enhanced stability for 2H-1,2,3- and 1H-1,2,4-triazoles attributed to the interaction of the unpaired electron pairs of the adjacent nitrogen atoms. Optimization of the geometry of 2H-1,2,3-triazole by the nonempirical methods showed that bases such as 6-21G and more expanded bases must be used and that electronic correlation should be taken into account. The use of updated calculation methods in the case of 1H-1,2,4-triazole did not give improved results.Prof. Asen Zlatarov University, 8010 Burgas, Bulgaria. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 5, pp. 645–651, May, 1998.     

Chemical data,ways and means,past and future

A brief outline of various data handling methods, from linear learning machines, principal component analysis, experimental design, and modeling to visualization, optimization, and validation together with a personal view on the historical development of the use of these methods, is given. Some future trends in handling chemical data are proposed as well. Copyright © 2014 John Wiley & Sons, Ltd.     

The determination of the equilibrium structures of oxygen,ozone, and hydrogen peroxide using the ab initio and density functional theory methods

The geometries and energies of small oxygen containing molecules are studied by both the ab initio and density functional theory (DFT) methods. The RHF, MP2, and QCISD(T) ab initio methods, BHandH, BHandHLYP, BeckeSLYP, Becke3P86 DFT hybrid methods, BLYP, and the BP86 non-local DFT methods with the 3-21G¹, 6-31G(d,p), 6-311 + G(2d,2p) and 6-311 + + G(3df,3pd) basis sets were used for the computational study. The obtained results from the different methods were compared to the experimental values. The suitability of the DFT methods for reproducing experimental data were discussed.     

Comparison of analytical methods: ICP-QMS,ICP-SFMS and FF-ET-AAS for the determination of V,Mn, Ni,Cu, As,Sr, Mo,Cd and Pb in ground natural waters

Three analytical methods, namely, inductively coupled plasma sector field mass spectrometry (ICP-SFMS); inductively coupled plasma quadrupole mass spectrometry (ICP-QMS) and filter-furnace electrothermal atomic-absorption spectroscopy (FF-ET-AAS) for the determination of V, Mn, Ni, Cu, As, Sr, Mo, Cd and Pb in ground natural water samples were compared and evaluated for their capacity to provide reliable and precise results. Two certified reference materials (SLEW-3 Estuarine Water; SLRS-4 River Water) were analysed to prove that accurate results could be obtained by using all the listed methods with properly optimised parameters. The limit of detection (LOD) for V, Mn, Ni, Cu, As, Sr, Mo, Cd and Pb provided by the ICP-MS methods ranged from 0.001 to 0.05 µg L^?1. Such LOD proved sufficient for the reliable determination of the listed elements in ground natural waters. However, the LOD of the FF-ET-AAS was approximately two orders of magnitude higher than that of ICP-MS, which made it impossible to quantify V, Mn, Ni, Mo and Pb. The effects of the usage of the collision cell mode in ICP-QMS and of the desolvation system Apex for ICP-SFMS to eliminate oxide ions levels were investigated. For all three analytical methods, the influence of the matrix effect on the results of the determination of the investigated elements using matrix model solution, external calibration and standard addition methods was evaluated. A comparison using a paired Student’s t-test between the results obtained by both ICP-MS methods for V, Mn, Ni, Cu, As, Sr, Mo, Cd and Pb concentrations in ground natural waters showed that there was no significant difference on a 95% confidence level. The precision of the results for ICP-SFMS, ICP-QMS and FF-ET-AAS varied between ~0.5 and 11; 2.5 and 12.5; 3 and 13.5%, respectively. Moreover, ICP-SFMS equipped with the desolvation system APEX proved a better choice for As, Cu and Mn analysis due to its better LOD (0.008, 0.03 and 0.02 µg L^?1, respectively) and precision (S_r ≤ 5.0; 7.5; 9.0%, respectively) compared to ICP-QMS and FF-ET-AAS.     

Evaluation of thin-layer chromatography methods for quality control of commercial products containing Aesculus hippocastanum, Turnera diffusa, Matricaria recutita, Passiflora incarnata, and Tilia occidentalis

In Mexico, plant-derived products with health claims are sold as herbal dietary supplements, and there are no rules for their legal quality control. Aesculus hippocastanum, Turnera diffusa, Matricaria recutita, Passiflora incarnata, and Tilia occidentalis are some of the major commercial products obtained from plants used in this region. In this paper, we describe the effectiveness of thin-layer chromatography methods to provide for the quality control of several commercial products containing these plants. Standardized extracts were used. Of the 49 commercial products analyzed, only 32.65% matched the chromatographic characteristic of standardized extracts. A significant number of commercial products did not match their label, indicating a problem resulting from the lack of regulation for these products. The proposed methods are simple, sensitive, and specific and can be used for routine quality control of raw herbals and formulations of the tested plants. The results obtained show the need to develop simple and reliable analytical methods that can be performed in any laboratory for the purpose of quality control of dietary supplements or commercial herbal products sold in Mexico.     

Application of derivative, derivative ratio, and multivariate spectral analysis and thin-layer chomatography-densitometry for determination of a ternary mixture containing drotaverine hydrochloride, caffeine, and paracetamol

New selective, precise, and accurate methods are described for the determination of a ternary mixture containing drotaverine hydrochloride (I), caffeine (II), and paracetamol (III). The first method uses the first (D1) and third (D3) derivative spectrophotometry at 331 and 315 nm for the determination of (I) and (III), respectively, without interference from (II). The second method depends on the simultaneous use of the first derivative of the ratio spectra (DD1) with measurement at 312.4 nm for determination of (I) using the spectrum of 40 microg/mL (III) as a divisor or measurement at 286.4 and 304 nm after using the spectrum of 4 microg/mL (I) as a divisor for the determination of (II) and (III), respectively. In the third method, the predictive abilities of the classical least-squares, principal component regression, and partial least-squares were examined for the simultaneous determination of the ternary mixture. The last method depends on thin-layer chromatography-densitometry after separation of the mixture on silica gel plates using ethyl acetate-chloroform-methanol (16 + 3 + 1, v/v/v) as the mobile phase. The spots were scanned at 281, 272, and 248 nm for the determination of (I), (II), and (III), respectively. Regression analysis showed good correlation in the selected ranges with excellent percentage recoveries. The chemical variables affecting the analytical performance of the methodology were studied and optimized. The methods showed no significant interferences from excipients. Intraday and interday assay precision and accuracy values were within regulatory limits. The suggested procedures were checked using laboratory-prepared mixtures and were successfully applied for the analysis of their pharmaceutical preparations. The validity of the proposed methods was further assessed by applying a standard addition technique. The results obtained by applying the proposed methods were statistically analyzed and compared with those obtained by the manufacturer's method.     

Calculated electron impact cross sections for the K-shell ionization of Fe,Co, Mn,Ti, Zn,Nb, and Mo atoms using the DM formalism

We used the Deutsch-Märk (DM) formalism to calculate atomic K-shell electron impact ionization cross sections for the elements Fe, Co, Mn, Ti, Zn, Nb, and Mo. The calculated K-shell ionization cross sections are compared with recently measured K-shell ionization cross sections. Good to satisfactory agreement was found for all atoms with the exception of Ti. Moreover, when compared to other available K-shell ionization cross sections for these atoms, calculated using other theoretical methods and semiempirical formulae, the predictions of the DM formalism achieve a level of agreement with experimental data that is as good or better than the predictions from the other methods.     

HPTLC Densitometric Quantification of Glycyrrhizin,Glycyrrhetinic Acid,Apigenin, Kaempferol and Quercetin from Glycyrrhiza glabra

Glycyrrhiza glabra Linn., commonly known as liquorice, is a reputed drug of Ayurveda. In the present work we developed and validated densitometric methods for quantification of glycyrrhizin, glycyrrhetinic acid, apigenin, kaempferol and quercetin using HPTLC. The developed methods were found to be precise and accurate. The amount of glycyrrhizin, glycyrrhetinic acid, and quercetin was found to be 1.070, 0.84 and 0.271% w/w, respectively. Apigenin and kaempferol were quantified in free (0.007 and 0.033% w/w) as well as bound (0.021 and 0.074% w/w) forms. This is the first report of simultaneous quantification of glycyrrhetinic acid and apigenin as well as kaempferol and quercetin from G. glabra. Furthermore, no TLC densitometric methods have been reported for the quantification of apigenin, kaempferol and quercetin from G. glabra.