Artificial Neural Networks Applied to Gas Mixture Analysis

1IntroduedonToanalyZehydrocarbongasndxtureS,asyStemconsistingofasuhablemulti-sereorarray,anaogUe-to-digitaconVerter(ADC)andacoInPuterfOrmulti-variatecalibrationalgorithInshasbameStablished[la].ThenonseledveandnonlinearresponsecharacteriaicsofchdricalsensorsareanirnPortantliInhaontoanalyzinmulti-coInPonatchdricamixtures.AmongthepotdriallyusefulnoulinearmAnods,anifioalneuralnfororks(ANN)arehighlypromising,mainlybecausetheANNisespedallysuitablefOrarbitrarynonlinearmaPpingbetWamsrmorres…     

Artificial Neural Networks Applied to the Quantitative Structure-Activity Relationship Study of Para-substituted Phenols

The artificial neural network (ANN) model with back-propagation of error is used to study the quantitative structure-activity relationship of para-substituted phenol derivatives between the biological activity and the physicochemical property parameters. Network parameters are optimized, and an empirical rule for dynamically adjusting the network's learning rate is proposed to improve the network's performance. The results showthat the three-layer ANN model gives satisfactory performance, with f(x)=1/(1+exp(-x)) as the network node's input-output transformation function and the number of hidden nodes 10. The network gives the mean square error (rose) of 0.036 when predicting the biological activity of 26 para-substituted phenol derivatives. This result compares favourably with that obtained by the conventional methods.     

Speciation Analysis of Osmium(VIII) and Osmium(IV) by UV‐VIS Spectrophotometry Using Quercetin as the Reagent

Abstract

The UV‐VIS spectrophotometric methods for the determination of Os(VIII) (as OsO₄) and Os(IV) (as OsCl₆ ^2? complex) in their mixtures were developed. Quercetin (Q), a flavonoid compound, was used as a chromogenic reagent. Both direct and derivative spectrophotometry can be employed for the determination of Os(VIII). The calculation of the first‐derivative spectrum of the examined mixture and the use of the signal at 285.1 nm allows reaching a better detection limit (0.01 µg mL^?1 Os) as compared with direct spectrophotometry (0.1 µg mL^?1 Os). Relative standard deviations of the results are in the range of 0.87%–4.65% and 0.45%–1.15% for direct and derivative mode, respectively. Selective redox reaction of OsO₄ with Q under the conditions used (0.05 M HCl, 1×10^?4 M Q, 15 min heating at 70°C) makes the basis of its determination in mixtures with the OsCl₆ ^2? complex. Quercetin does not react with the OsCl₆ ^2? complex. The signals of the OsCl₆ ^2? complex can be isolated from the examined mixtures by the calculation of the third‐order derivative spectra and the use of the values at 340.0 nm. The effectiveness of the reduction of OsO₄ in chloride solutions has been studied by the developed method.     

Simultaneous Determination of Gold and Platinum by Double Artificial Neural Network Analysis with Flow-injection

A highly sensitive double artificial neural network （DANN） analysis with flow-injection chemiluminescence （FI-CL） has been developed to simultaneously determine the trace amounts of the gold and platinum in simulated mixed samples, without the boring process.     

Simultaneous Determination of Gold and Platinum by Double Artificial Neural Network Analysis with Flow-injection Chemiluminescence

Chemiluminescence (CL) is well known to be an important and powerful analytical technique owing to its lower detection limits, higher sensitivity and wider linear ranges can be achieved with simpler instrument1. CL analysis has been used for determination…     

Quantitative Determination of Nadolol in Tablets by High‐Performance Liquid Chromatography and UV‐Derivative Spectrophotometry

Abstract

High‐performance liquid chromatographic (HPLC) and UV derivative spectrophotometric (UVDS) methods were developed and validated for the quantitative determination of nadolol in tablets. The HPLC method was performed on a C18 column with fluorescence detection. The excitation and emission wavelengths were 230 and 300 nm, respectively. A mobile phase composed by acetonitrile‐water containing 0.1% triethylamine (15∶85 v/v) and pH adjusted to 4.6 with formic acid was used. The UVDS method was performed taken a signal at 279.5 nm. The correlation coefficient (r) obtained for both methods was 0.9999. The proposed methods are simple, precise, accurate, and can be used in routine analysis.     

Comparison of Artificial Neural Networks with Partial Least Squares Regression for Simultaneous Determinations by ICP-AES

Simultaneous determination of several elements （U, Ta, Mn, Zr and W） with inductively coupled plasma atomic emission spectrometry （ICP-AES） in the presence of spectral interference was performed using chemometrics methods. True comparison between artificial neural network （ANN） and partial least squares regression （PLS） for simultaneous determination in different degrees of overlap was investigated. The emission spectra were recorded at uranium analytical line （263.553 nm） with a 0.06 nm spectral window by ICP-AES. Principal component analysis was applied to data and scores on 5 dominant principal components were subjected to ANN. A 5-5-5 （input, hidden and output neurons） network was used with linear transfer function after both hidden and output layers. The PI,S model was trained with five latent variables and 20 samples in calibration set. The relative errors of predictions （REP） in test set were 3.75% and 3.56% for ANN and PLS respectively.     

Conformational Analysis of C‐Trehaloses Using Molecular Mechanics Calculations

Relaxed‐residue energy maps based on the MM3 force field were computed for the three C‐linked (1‐1) d‐glucosyl disaccharides, C‐trehaloses: the axial–axial linked α,α‐trehalose, the axial–equatorial α,β‐trehalose and the equatorial–equatorial linked β,β‐trehalose. Optimized structures were calculated on a 20°‐grid spacing of the torsional angles about the C‐glycosidic bonds. Boltzman weighted ³J coupling constants were calculated and compared to the experimental values; they are satisfactory. The general shape of the energy maps indicates that α,α‐trehalose is a quite rigid molecule adopting only one conformation around the C‐glycosidic linkage, whereas the other two isomers are rather flexible. Compared to the corresponding O‐disaccharides α,β‐ and β,β‐trehaloses exhibit a larger number of low energy conformers and a larger area of the map energy < 8 kcal/mol. The preferred conformations of the axial C‐glycosidic bond are in agreement with the exo‐anomeric effect. Equatorial C‐ glycosidic bonds are rather flexible, influenced by the polarity of the milieu and the formation of interresidue hydrogen bonds.     

Predicting the Standard Enthalpy (ΔHo f) and Entropy (So) of Alkanes by Artificial Neural Networks

Abstract

Artificial Neural Networks (ANNs) with Extended Delta-Bar-Delta (EDBD) back propagation learning algorithm have been developed to predict the standard enthalpy and entropy of 87 acyclic alkanes. Molecular weight, boiling point and density of the compounds were used as input parameters. The network's architecture and parameters were optimized to give maximum performances. The best network was a 3-6-2 ANN, and the optimum learning epoch was about 1320. The results show that the maximum relative errors of enthalpy and entropy are less than 3%. They reveal that the performances of ANNs for predicting the enthalpy and entropy of alkanes are satisfying.     

Electrochemical Analysis of Mercury Using a Kryptofix Carbon‐Paste Electrode

Abstract

Successful applications of different analytical procedures to determine quantitatively mercury in aqueous media can be found in recent literature. Fundamentally it has made use of Cold Vapour Atomic Absorption Spectrometry (CV‐AAS), X‐Ray Fluorescence or UV Spectrophotometry, Inductively Coupled Plasma Atomic Emission Spectrometry (ICP‐AES), or Inductively Coupled Plasma Mass Spectrometry (ICP‐MS), which are the techniques commonly used for trace measurement of heavy metal in the laboratory. In this paper a new and alternative methodology to determine quantitatively mercury in aqueous media is reported. A kryptofix carbon‐paste electrode has been used to determine voltammetrically mercury. The detection limit for mercury was evaluated to be 0.12 µg/l.     

About the Possibility of Simulation the Discharge Characteristics of Lithium–Sulfur Batteries Using Fuzzi Neural Networks

Russian Journal of Electrochemistry - In this work we considered the possibility of simulation of changes in the characteristics of lithium-sulfur batteries during cycling using an Adaptive...     

Quantitative assessment of organic compounds adsorbed on silica gel by FTIR and UV–VIS spectroscopies: the contribution of diffuse reflectance spectroscopy

Different spectroscopic methods are compared to quantitatively determine organic compounds adsorbed or grafted on silica. The studied example is a derivative 1 of a well known photosensitizer, benzophenone. Transmission FTIR, diffuse reflectance FTIR (DRIFT) and UV (DRUV) spectroscopy are used to measure the concentration of adsorbed 1 on silica. The diffuse reflectance spectra are treated according to the Kubelka–Munk theory. It is shown that for such a compound absorbing in the UV range, DRUV spectra actually display a linear correlation between the remission function F(R) and the concentration of adsorbed 1. As this method neither implies any sample preparation nor any problems arising from the supporting silica, it proves to be fast, efficient and with a low detection threshold. For the IR spectra, it is necessary to numerically substrate the spectrum of silica which absorbs the light in this range. Provided that some care is paid to this numerical treatment which takes the sample heterogeneity into account, transmission and DRIFT spectra also display a linear correlation between the absorbance or the F(R) function and the concentration of adsorbed 1. However, sample preparation is much easier for DRIFT spectra as no pellets are made. Moreover, the DRIFT spectra of ground samples appear easier to process than the transmission spectra because of a better baseline and resolution. Although less resolved under 1500 cm⁻¹, the DRIFT spectra of non-ground samples can also be processed and give satisfactorily and rapid results without any possible perturbation of the structural integrity of the sample.     

HPLC‐UV Detection for Analysis of p‐Benzoquinone Dioxime and p‐Nitrosophenol,and Chromatographic Fingerprint Applied in Quality Control of Industrial p‐Benzoquinone Dioxime

Abstract

A reliable reversed‐phase high performance liquid chromatographic (HPLC) method has been developed for simultaneous determination of p‐benzoquinone dioxime (BQD) and its related impurity p‐nitrosophenol (NSP). Separation was achieved on a Kromasil C₁₈ column by using methanol‐water‐NH₄Ac‐NH₃ solution (pH=7.0, 50 mM) (30/50/20, v/v/v) as the mobile phase, and detection was operated by UV absorption at a wavelength of 305 nm. The method was seen to have good linearity, accuracy, and precision for the concentration range and to be an attractive choice for the quality control of BQD for industrial use. Moreover, the HPLC‐UV‐vis fingerprint of BQD has been established, and successfully applied to quality control of industrial BQD in laboratories of some rubber factories in China. Chromatographic fingerprints of intermediates would become an effective strategy for accelerating the progress of fine chemical industry.     

Identification and Quantitative Analysis of Nucleosides and Nucleobases in Aqueous Extracts of Fritillaria Cirrhosa D. Don. Using HPLC–DAD and HPLC-ESI-MS

Bulbus Fritillariae cirrhosae is the most widely used medicinal herb for antitussive and apophlegmatic in China and commonly prepared as a water decoction. For clarifying the water-soluble components in Fritillaria cirrhosa D. Don., a simple and sensitive method was developed using high performance liquid chromatography coupled with a photodiode array detector (HPLC-DAD) and an electrospray ionization mass spectrometer (HPLC-ESI/MS) for the quantitative determination and identification of 10 nucleosides and nucleobases. Of the 10 compounds, two (2-deoxyadenosine and hypoxanthine) were identified and determined in F. cirrhosa for the first time. The 10 compounds were separated using a Zorbax SB-Aq column with a gradient elution of methanol and water. All the calibration curves showed good linearity (r² ≥ 0.9991). The recoveries were between 97.7% and 103.5%. The method was validated with respect to precision, repeatability and accuracy, and was successfully applied to the simultaneous determination of the 10 analytes in 24 batches of F. cirrhosa, collected from different parts of China. This report provided a firm basis for clarifying the pharmacological effect and comprehensively evaluating the quality of F. cirrhosa and related preparations.     

Spectrophotometric Flow Injection Analysis of Sulfite and Formaldehyde In Aqueous Micellar Medium Using 5,5′-Dithiobis(2-Nitrobenzoic Acid)

Abstract

Aqueous sulfite and formaldehyde were quantitated in the nanomole range using the reaction of 5,5′-dithiobis(2-nitrobenzoic acid), DTNB, with sulfite. Cationic micelles were used and found to greatly increase the sensitivity, bathochromically shifting the absorption spectra as well as lowering the pK of the reaction. the method was adapted to flow injection analysis, allowing more than 100 samples to be analyzed per hour with a relative standard deviation of less than 1.5% in all cases studied. the method is simple, fast and more sensitive than any available methods. the great flexibility of the choice of pH, surfactant concentration and buffer concentration contributes much to the high precision that could be achieved.     

Quantitative Analysis of Terbutaline (Bricanyl®) in Human Plasma with Liquid Chromatography and Electrochemical Detection Using On-Line Enrichment

Abstract

A liquid chromatographic method with electrochemical detection (LC-EC) has been developed for the quantitative analysis of terbuta-line in the range 5–50 pmole ml^?1 of human plasma. Terbutaline is isolated from 2 ml of plasma on an ion-exchange column and the eluate is concentrated on a hydrophobic precolumn on-line in the chromatographic system. The precolumn is then back-flushed for further separation onto a hydrophobic analytical column. The mobile phase is a methanol-aqueous buffer to which sodium perchlorate is added to achieve resolution from interfering peaks. A glassy carbon electrode is used for detection. Comparison has been made with gas chromatography-mass spectrometry (GC-MS) to examine the accuracy of the method.     

Synthesis of H‐Phosphinates by the UV Light–Mediated Fragmentation‐Related Phosphorylation Using Simple P‐Heterocycles

Photolysis of aryl‐substituted 2,5‐dihydrophosphole oxides (5a–e and 8) in the presence of methanol afforded methyl aryl‐H‐phosphinates (2a–e) in good yields. In the case of 1‐ethyl‐, cyclohexyl‐, or ethoxy‐2,5‐dihydrophosphole oxides, the reaction was much slower (5f and 5h) or did not take place at all (5g). In such instances, the presence of an additional skeletal methyl group (7) or the use of the more strained 7‐phosphanorbornene derivatives (6) promoted the fragmentation‐related phosphorylations. Furthermore, the effect of the ring saturation in 8 and the possible extensions to 2‐phosphabicyclo[3.1.0]hexanes (10a and 10f), a 1,2‐dihydrophosphinine oxide (11), and a 1,2,3,4,5,6‐hexahydrophosphinine oxide (12) were also investigated. Model compounds with P‐phenyl substituent that are of sufficient ring strain (8, 10a, and 11) could be utilized well.     

GC�CMS and GC�CNPD Determination of Formaldehyde Dimethylhydrazone in Water Using SPME

Formaldehyde dimethylhydrazone (FADMH) is one of the important transformation products of residual rocket fuel 1,1-dimethylhydrazine (1,1-DMH). Thus, recent studies show that FADMH toxicity is comparable to that of undecomposed 1,1-DMH. In this study, a new method for quantification of FADMH in water based on solid phase microextraction (SPME) in combination with gas chromatography (GC) with mass spectrometric (MS) and nitrogen-phosphorus detection (NPD) is presented. Effects of SPME fiber coating type, extraction and desorption temperatures, extraction time, and pH on analyte recovery were studied. The optimized method used 65 micron polydimethylsiloxane/divinylbenzene fiber coating for 1?min headspace extractions at 30?°C. Preferred pH and desorption temperature from the SPME fiber are >8.5 and 200?°C, respectively. Detection limits were estimated to be 1.5 and 0.5?μg?L(-1) for MS and NPD, respectively. The method was applied to laboratory-scale experiments to quantify FADMH. Results indicate applicability for in situ sampling and analysis and possible first-time detection of free FADMH in water.