Simplified data processing for the simultaneous determination of catalysts by catalytic kinetics

An approximate equation for data processing is proposed for the simultaneous determination of catalysts by catalytic kinetics. On applying the equation to the reaction between two reactants catalysed by two catalysts, the calculation is simplified to that of only one reactant, simplifying the experiment and data processing. The equation was used to treat the simultaneous determination of ruthenium and osmium with Ce(IV)As(III) as the indicator reaction, with the results in good agreement with those using the exact equation.     

A new kinetic photometric method for the simultaneous determination of metals based on catalytic and activating effects

Summary The potential use of the activating effect of Pb(II) on the Mn(II)-catalysed oxidation of Tiron by hydrogen peroxide in the presence of 1,10-phenanthroline for the simultaneous determination of the two metals was investigated. The results obtained allowed the development of a new kinetic photometric method for the simultaneous determination of Pb(II) and Mn(II). The catalysed reaction was monitored by the initial rate method, which was applied to absorbance-time curves. Different Mn(II) concentrations were used to construct calibration graphs by plotting the slopes of the photometric curves obtained against the Mn(II) concentration at each Pb(II) concentration assayed. A new calibration graph was obtained in terms of the Pb(II) concentration from the slopes of such graphs. By applying the standard-addition method to the sample to be assayed a third graph was obtained, the slope and intercept of which provided the analytical concentration of Pb(II) and Mn(II), respectively. The optimized values of the different variables involved were used to determine Mn(II) and Pb(II) over the concentration ranges 1–5 and 200–800 ng/ml, respectively.     

New analytical technique for the simultaneous determination of aromatic amines

Summary A new and sensitive analytical technique has been developed for the simultaneous determination of six aromatic amines. It is based on the differential migration of coloured derivatives formed by the reaction of the diazotized amines with 6-amino-1-naphthalene-3-sulphonic acid on a silica gel plate. The concentration is evaluated by colour comparison or by spectrophotometry under the influence of a temperature gradient. The method is highly reproducible and has been applied to the determination of amines in environmental samples. Standard deviations are 4.6–7.3%.     

Heterogenized methylaluminoxane and isobutylaluminoxane as activators for metallocene catalysts

Heterogenized alkylaluminoxanes prepared in situ on the montmorillonite (MMT) surface by the partial hydrolysis of AIR₃ with water of the support are effective activators for metallocenes. The thermal destruction of isobutylaluminoxane molecules in the MMT-H₂O/Al(i-Bu)₃ system has been studied by the temperature-programmed desorption method coupled with mass spectrometry (TPD-MS). The process begins at a lower temperature and is more complicated than the destruction of methylaluminoxane (MAO) in MMT-H₂O/AlMe₃. Isobutyl-substituted aluminoxane and the ansa-metallocene Me₂Si(Ind)₂ZrCl₂ form metal-alkyl complexes that are more active in propylene polymerization than methyl-substituted aluminoxane. The TPD-MS study of the initial stages of gas-phase ethylene and propylene polymerization shows that the nature of the metallocene in the heterogenized metallocene catalysts is an essential factor in the distribution of active sites by the activation energy of the thermal destruction of active Zr-C bonds.     

A graphical derivative approach to the photometric determination of lutetium and praseodymium in mixtures

The reaction of lanthanides with 1,4-dihydroxyanthraquinone has been examined and optimum conditions have been found for the separate spectrophotometric determination of Lu and Pr. A graphical method based on use of first and second derivative spectra has been developed for analysis of binary mixtures of the two, in concentration ratios from 1:5 to 5:1. Linear calibration curves were obtained between 1 and 10 mug/ml.     

Green approach using monolithic column for simultaneous determination of coformulated drugs

Green chemistry and sustainability is now entirely encompassed across the majority of pharmaceutical companies and research labs. Researchers’ attention is careworn toward implementing the green analytical chemistry principles for more eco‐friendly analytical methodologies. Solvents play a dominant role in determining the greenness of the analytical procedure. Using safer solvents, the greenness profile of the methodology could be increased remarkably. In this context, a green chromatographic method has been developed and validated for the simultaneous determination of phenylephrine, paracetamol, and guaifenesin in their ternary pharmaceutical mixture. The chromatographic separation was carried out using monolithic column and green solvents as mobile phase. The use of monolithic column allows efficient separation protocols at higher flow rates, which results in short time of analysis. Two‐factor three‐level experimental design was used to optimize the chromatographic conditions. The greenness profile of the proposed methodology was assessed using eco‐scale as a green metrics and was found to be an excellent green method with regard to the usage and production of hazardous chemicals and solvents, energy consumption, and amount of produced waste. The proposed method improved the environmental impact without compromising the analytical performance criteria and could be used as a safer alternate for the routine analysis of the studied drugs.     

A photometric method for the determination of oxalic acid

Summary A method for the quantitative determination of oxalic acid based onEegriwe's color test for glycolic acid is described. The principle of the method is the reduction of oxalic to glycolic acid by nascent hydrogen from magnesium powder and dilute sulfuric acid. By heating with a solution of 2,7-dihydroxynaphthalene in concentrated sulfuric acid formaldehyde splitt off from glycolic acid condensates with the reagent, tetrahydroxydinaphthylmethane forms and is oxidized to a deep colored dye-stuff by atmospheric oxygen.A study of interfering substances and the way of avoiding their influence was made.The color system, under the conditions of the method, follows theLambert-Beer's law. With the exception of a photoelectric colorimeter, no special equipment is required. The procedure is very simple, possesses great sensitivity, and may be applied with minor variations to a wide variety of materials.

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Zusammenfassung Es wird ein Verfahren zur quantitativen Bestimmung der Oxalsäure beschrieben, das auf der Farbreaktion nachEegriwe für Glykolsäure beruht. Das Prinzip der Methode beruht auf der Reduktion der Oxalsäure zu Glykolsäure durch nascierenden Wasserstoff aus Magnesiumpulver und verd. Schwefelsäure. Durch Erhitzen mit einer Lösung von 2,7-Dioxynaphthalin in konz. Schwefelsäure wird der abgespaltene Formaldehyd mit dem Reagens kondensiert. Es bildet sich Tetraoxydinaphthylmethan, welches durch den Luftsauerstoff zu einem intensiv gefärbten Produkt oxydiert wird. Der Einfluß störender Substanzen und dessen Vermeidung werden untersucht. Die Farbreaktion folgt unter den geschilderten Versuchsbedingungen demLambert-Beerschen Gesetz. Mit Ausnahme eines photoelektrischen Kolorimeters ist kein besonderer Aufwand erforderlich. Die Methode ist sehr einfach und von großer Empfindlichkeit. Sie kann mit geringfügigen Abänderungen für verschiedenartiges Untersuchungsmaterial angewendet werden.

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Résumé On décrit une méthode pour le dosage quantitatif de l'acide oxalique, basé sur le test coloré d'Eegriwe pour l'acide glycolique. Le principe de la méthode repose sur la réduction de l'acide oxalique en acide glycolique par l'hydrogène naissant produit avec le magnésium en poudre et l'acide sulfurique dilué. En chauffant avec une solution de dihydroxy-2,7 naphtalène dans l'acide sulfurique concentré, le formaldéhyde se libère du produit de condensation entre l'acide glycolique et le réactif; le tétrahydroxydinaphtylméthane se forme et s'oxyde en une matière colorante foncée sous l'action de l'oxygène atmosphérique.On a fait une étude des substances interférentes et de la manière d'éviter leur influence.Le système coloré, dans les conditions de la méthode, suit la loi deLambert-Beer. A l'exception d'un colorimètre photoélectrique, aucun équipement spécial n'est nécessaire. Le mode opératoire est très simple, possède une grande sensibilité et peut être appliqué avec de minimes variations à un grand nombre de substances.

     

Vanadox--a new reagent for the photometric determination of vanadium

A new reagent, 2,2-dicarboxydiphenylamine, vanadox, is proposed for the photometric determination of vanadium in steels, high temperature alloys and ferrotitanium ores. In strongly acidic medium the reagent is selective for vanadium(V) and only eerium(IV) interferes.     

Rapid photometric method for the determination of taurine and cysteic acid

A method is described for the rapid determination of microgram quantities of taurine or cysteic acid in the presence of relatively large amounts of other amino-acids. Dinitrophenylation of the sample followed by chloroform extraction yields an aqueous solution containing only DNP-taurine or DNP-cysteic acid, the absorbance of which gives a direct measure of these components.     

New voltammetric procedure for the simultaneous determination of copper and mercury in environmental samples

Summary A new voltammetric procedure for the simultaneous determination of Cu and Hg down to the ng/l-range in environmental samples is described. Differential pulse anodic stripping voltammetry (DPASV) at a gold electrode is applied. There are two versions. For Hg-levels typically below 100 ng/l in presence of substantially higher Cu-concentrations (300 ng/l or more), e.g. in sea water, Hg has to be determined by the subtractive mode of DPASV at a twin gold electrode and programmed polarisation has to be applied during the cathodic deposition stage, while the usually higher Cu-levels can be determined by common DPASV at a normal gold electrode. For Hglevels above 100 ng/l the determination of Hg and Cu can be performed in the same run by common DPASV at a normal gold electrode. The application of the gold electrode always requires medium exchange to 0.1 M HClO₄ plus 2.5×10^–3 M HCl subsequent to the cathodic accumulation stage before stripping. The method has been successfully applied to natural waters and wine. The necessary sample pretreatment remains simple and consists just in UV-irradiation to release the trace metal amount bound to dissolved organic matter, which is performed with samples from natural waters after prior 0.45 -filtration to separate from suspended particulate material.

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Neues voltammetrisches Verfahren zur simultanen Bestimmung von Kupfer und Quecksilber in Umweltmaterial

Zusammenfassung Als Bestimmungsverfahren werden zwei Versionen der differentiellen Pulsinversvoltammetrie (DPASV) an der Goldelektrode eingesetzt. Bei Quecksilbergehalten typisch unter 100 ng/l und gleichzeitiger Anwesenheit höherer Kupferkonzentrationen (300 ng/l), wie z.B. im Meerwasser, muß Hg mit der subtraktiven DPASV an einer Zwillingselektrode aus Gold bestimmt werden und während des kathodischen Anreicherungsschrittes erfolgt programmierte Polarisation der Goldelektrode. Hingegen können die gewöhnlich höheren Cu-Gehalte mit der üblichen konventionellen DPASV an einer normalen Goldelektrode bestimmt werden. Bei Hg-Gehalten oberhalb 100 ng/l kann die Bestimmung von Hg und Cu in einem voltammetrischen Arbeitsgang mit der konventionellen üblichen DPASV an einer normalen Goldelektrode erfolgen. Die Verwendung der Goldelektrode verlangt immer Wechsel des Mediums zu 0,1 M HClO₄ plus 2,5 ×10^–3 M HCl nach der kathodischen Anreicherung vor der stripping-Phase. Die Methode hat erfolgreiche Anwendung bei der Untersuchung natürlicher Gewässer und von Wein gefunden. Die erforderliche Probenvorbereitung bleibt einfach und besteht in einer UVBestrahlung, um den durch gelöste organische Materie gebundenen Spurenmetallanteil zu mobilisieren. Bei Proben aus natürlichen Gewässern erfolgt vorher eine 0,45 -Filtration zur Abtrennung von Schwebstoffen.

     

New approach to the preparation of catalysts for the oxidative coupling of methane

A new approach to the preparation of systems that exhibit catalytic activity in the oxidative coupling of methane (OCM) is considered. With the use of ferrospheres separated from power-generation ashes from different sources as an example, it was demonstrated that OCM catalysts can be prepared by the crystallization/solidification of oxide melts with the formation of microspherical particles. The dependence of activity and selectivity for the oxidative reforming of methane on the ferrospheres containing from 36.2 to 92.5 wt % Fe₂O₃ into the products of deep oxidation and OCM was studied. It was found that deep oxidation reactions on ferrospheres with Fe₂O₃ contents higher than 85% were suppressed, and the main reaction path of CH₄ conversion was its oxidative coupling with the formation of C₂ products (with selectivity to 60% at 750°C); moreover, the selectivity for C₂ formation in this region was proportional to the concentration of Fe₂O₃. Phases responsible for the catalytic conversion of methane into CO _x and OCM products were considered, and it was shown that the catalytic activity and selectivity of the oxidative transformation of CH₄ on ferrospheres is determined by the position of the point that corresponds to their composition on a phase diagram of CaO-Fe₂O₃-SiO₂.     

Direct and simultaneous determination of metal impurities in catalysts based on platinum group elements

Production of new catalysts requires effective analytical quality control. The study of trace element composition of heterogeneous catalysts, based on C+PdO, using atomic emission spectrometry (AES) was carried out. A new method for the direct solid-state analysis by means of AES with direct current arc discharge was developed. On the basis of the qualitative analysis of elements, Al, Fe, Ni, Si and Ti have been identified, and for these elements, the quantitative method of determination has been developed. Optimization of excitation parameters and validation of the analytical method are presented. Calibration samples of the following composition were prepared: graphite powder (as a matrix), 3% of PdO and increasing contents of determined element oxides (spectrally pure). Calibrations were calculated by means of the least squares method. Working range for element impurities was from 1% to 0.0003%, and the limits of quantification — LOQ, (10-σ criterion) varied in the range from 0.002% (Ti) to 0.0038% (Si). For the control of active component, palladium was calibrated (working range — 0.01%–10.00%; LOQ ?0.027%). The developed method can be used, also, for the elemental determinations of the other carbon based catalysts with the different active components (of platinum group elements).      

Rapid method for the photometric determination of manganese in ores and alloys

Summary A procedure for the rapid photometric determination of manganese in the range of 4–24 mg/50 ml, is based on the oxidation of manganese(II) to manganese(III) by excess potassium dichromate in a medium of 8.0 to 9.0 M phosphoric acid at room temperature. Interferences are few when compared to the methods currently available. The method can be successfully employed for the estimation of manganese in ores and alloys and the results obtained compare favourably with standard methods. The method is therefore recommended for adaption for rapid routine analysis.

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Schnelle Methode zur photometrischen Bestimmung von Mangan in Erzen und Legierungen

Zusammenfassung Ein Verfahren zur raschen Bestimmung von Mangan im Bereich von 4–24 mg/50 ml wird beschrieben. Es beruht auf der quantitativen Oxydation von Mn(II) zu Mn(III) mit Dichromat in 8,0–9,0 M phosphorsaurer Lösung bei Raumtemperatur. Die Störmöglichkeiten sind geringer als bei sonst üblichen Methoden. Das Verfahren wurde mit Erfolg zur Manganbestimmung in Erzen und Legierungen angewendet und gute Übereinstimmung mit Standardmethoden erzielt. Es wird für die schnelle Routineanalyse empfohlen.

     

Dual-flame photometric detector (DFPD) for the simultaneous G. C. determination of P-, S-, Cl-containing organic compounds

Summary The construction and set-up of a dual-flame photometric detector (DFPD) which, through three channel operation, allows the simulatneous selective determination of P-, S-, Cl-containing compounds eluted from a G. C. column is described. For P- and S-containing compounds the molecular emission bands HPO and S₂ at 526 and 394 nm respectively are measured; for Cl-containing compounds, after reaction with In, the InCl band at 360 nm is recorded. Detectability, specificity, linearity as well as mutual interferences are discussed and compared with those of classical GC-detectors as thermionic (TID) and electron capture (ECD). Some practical applications concerning the pesticide residue analysis in animal and vegetable extracts are shown.

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Zwei-Flammen-Photometer-Detektor (DFPD) für die gleichzeitige G. C. Bestimmung von P-, S-und Cl-enthaltenden organischen Verbindungen

Zusammenfassung Der Aufbau und die Justierung eines Zwei-Flammen-Photometer-Detektors, welcher durch 3-Kanal Arbeitsweise eine gleichzeitige selektive Bestimmung von P-, S- und Cl-enthaltenden Verbindungen erlaubt, wird beschrieben. Für P- und S-enthaltende Moleküle werden die Molekül-Linien HPO und S₂ bei 526 bzw. 394 nm gemessen; bei Cl-enthaltenden Verbindungen wird, nach Reaktion mit In, die InCl-Linie bei 360 nm registriert. Nachweisgrenze, Spezifität, Linearität sowie Quereinflüsse wechselseitiger Interferenzen werden diskutiert und mit den entsprechenden Werten klassischer GC-Detektoren wie TID und ECD verglichen. Einige praktische Anwendungen bei der Pestizid-Rückstand-Analyse in Extrakten von Tieren und Pflanzen werden gezeigt.

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Détecteur photométrique à double flamme (DPDF) pour la détermination simultantée des composés organiques contenant du P, S, Cl en CG

Résumé On décrit la construction et la mise au point d'undétecteur photométrique à double flamme («DFPD»=DPDF); celui-ci permet grâce à système à «3 canaux» de déterminersimultanément et sélectivement les substances organiques contenant du P, du S, du Cl, à la sortie des colonnes de chromatographie en phase gazeuse. Pour les substances contenant du P et du S, on mesure l'émission moléculaire correspondant aux bandes dûes à HPO et S₂ (526 et 394 nm. respectivement); pour les composés chlorés, on mesure l'émission correspondant à la bande due à InCl (360 nm.) après réaction avec l'Indium des gaz brulés. Les problèmes relatifs à la limite de détection, à la specificité et à la linéarité de la réponse en fonction de la quantité de substance injectée, ainsi qu'aux interactions entre substances détectées, sont discutés et les rultats obtenus sont compar avec ceux fournis par les détecteurs classiques: thermo-ionique («TID»=DTI) ou à capture d'électrons («ECD»=DCE). Quelques applications pratiques dans le domaine de l'analyse des résidus de pesticides dans des extraits d'origine animale ou végétale sont données comme exemples.

     

Towards the rational design of palladium-N-heterocyclic carbene catalysts by a combined experimental and computational approach

A combined experimental and computational approach towards the development of Pd-NHC catalysts is described. A range of benzimidazolylidinium ligands incorporating electron-rich and electron-poor substituents were prepared and evaluated in the Suzuki reaction. The most electron-rich ligand showed the highest catalytic activity. Based on this information, the first alkyl-alkyl Negishi cross-coupling reaction protocol was developed. Evaluation of N,N′-diaryl-(4,5-dihydro)imidazolylilidinium ligands showed a strong dependence on the steric topography around the metal centre. A computational study of the most active ligand in the Negishi reaction, its Pd(0) and PdCl₂-complexes and related structures were modelled at the B3LYP/DZVP and HF/3-21G levels of theory. The potential energy hypersurfaces flattened with increase in ligand size. Binding energies were computed for carbene/Pd(0) adducts (in the range ∼31-40 kcal mol⁻¹), roughly double that for PH₃ (∼16 kcal mol⁻¹). Weak intramolecular interactions were found using AIM analyses.