Capacity factors and peak widths in the gradient elution reversed phase separation of high molar mass polystyrenes

Summary A simplex method for determining the constantsS andk _o from the equation lnk’=lnk _o−S ϕ (was developed and applied to the reversed phase separation of high molar mass polystyrenes using gradients of any curvature. Experimental retention times described using the equation had a standard deviation of 1.1%. The inclusion of a quadratic term in the equation was found to be unwarranted. BothS and lnk _o varied linearly with ln molar mass. The logarithm of peak width of an eluting polystyrene peak was found to be a linear function of the mobile phase composition at elution. The slope was equal toS.     

An alternative approach for predicting peak width in gas chromatography

Summary The linear relationship between natural logarithm of width factor (lnp′)and natural logarithm of retention factor (lnk) is demonstrated. This relationship is then used to establish the relationship between (lnp′), absolute temperature (T), and carbon number (z), as follows: Inp′=A+bz+c/T+dz/T where A, b, c and d are thermodynamically related constants. The above equation is used to predict the unadjusted widths (w _R ) ofn-alkanes, fatty alcohols and fatty acid methyl esters (FAMEs) at various temperatures, predicted values are in good agreement with experimental values. The above equation can be used to predict the width of FAMEs from rice bran oil. The largest difference between the experimental and predicted values is 0.66 s or 6.32%.     

Numerical investigation of the uncertainty of Arrhenius parameters

The temperature dependence of rate coefficient k is usually described by the Arrhenius expression ln k = ln A − (E/R)T ⁻¹. Chemical kinetics databases contain the recommended values of Arrhenius parameters A and E, the uncertainty parameter f (T) of the rate coefficient and temperature range of validity of this information. Taking ln k as a random variable with known normal distribution at two temperatures, the corresponding uncertainty of ln k at other temperatures was calculated. An algorithm is provided for the generation of the histogram of the transformed Arrhenius parameters ln A and E/R, which is in accordance with their 2D normal probability density function (pdf). The upper and the lower edges of the 1D normal distribution of ln k correspond to the two opposite edge regions of the 2D pdf of the transformed Arrhenius parameters. Changing the temperature, these edge regions move around the 2D cone. The rate parameters and uncertainty data belonging to reactions H + H₂O₂ = HO₂ + H₂ and O + HO₂ = OH + O₂ were used as examples.     

Microgravity experiments on colloidal crystallization of silica spheres in the presence of sodium chloride

 Rate coefficients (k) in the colloidal crystallization of monodispersed silica spheres in the presence of sodium chloride are studied in microgravity achieved by parabolic flights of an aircraft. Time-resolved reflection spectroscopy is made with a continuous circulating-type stopped-flow cell system. The k values decrease as the salt concentration increases both at 0 and 1 G and those in microgravity are smaller than those in normal gravity by 16% (maximum), especially in water and in the presence of a small amount of the salt lower than 2 × 10⁻⁶ mol/l. The rates in flight at 1 G are larger by 15% (maximum) compared with those at 1 G on the ground. The k values obtained at 0 G, 1 G in flight and 1 G on the ground agree excellently with each other for the suspensions with 3 × 10⁻⁶ and 4 × 10⁻⁶ mol/l sodium chloride. Disappearance of the downward diffusion of spheres and no convection of the suspensions are important for retardation in microgravity. Received: 20 January 2000 Accepted: 9 March 2000     

Influence of temperature and mobile phase composition on retention properties of oligomeric bonded phases in reversed-phase liquid chromatography (RPLC)

Summary The effect of temperature and mobile phase composition (methanol-water) on the retention behaviour of an oligomeric series of n-octylsilyl bonded phases in reversed-phase liquid chromatography has been investigated. Plots of lnk against 1/T (van't Hoff plot) and the enthalpy of transfer (ΔH^o) yields linear relationships under the conditions studied. The ΔH^o values of the aromatic hydrocarbons and n-alkyl benzoates are higher than those of the polar compounds due to their higher level of interaction with the stationary phase. A linear plot of ΔH^o vs. ΔS^o suggest that the retention process, which is essentially controlled by non-specific (dispersive) interactions between the solutes and the bonded ligands, is identical for all cases evaluated. The existence of similar retention mechanisms is confirmed by the constant value of the enthalpy-entropy compensation temperature of the columns for a given class of componds. As expected, decreasing the methanol content (% v/v) of the mobile phase results in increased eluite retention times. The methylene and phenyl selectivities are found to be independent of the carbon content of the stationary phases and varied only with the eluent composition. In addition to their high stability under aggressive mobile phase conditions as previously reported, the results of this study generally showed that the solute retention process on oligomeric phases are similar to those exhibited by the conventional reversed phases.     

Chromatographic Behavior of C60 and C70 Fullerenes at Subambient Temperature with n-Alkanes Mobile Phases

The influence of temperature on the retention and separation of C60 and C70 fullerenes was studied under HPLC conditions. Particularly, chromatographic experiments were conducted using moderate carbon loaded octadecylsilica stationary phase and homologous series of n-alkanes including n-pentane, n-hexane and n-heptane as the mobile phases. All studies were performed across wide range of subambient temperature from −80 to +20 °C. From practical point of view the best chromatographic conditions for baseline separation of the components of interest were selected. The retention of analytes was strongly affected by temperature and below minus 30 °C strong deviation from van't Hoff behavior was observed. To explore this phenomenon selected thermodynamic parameters including changes of enthalpy (ΔH^o) and changes of entropy (ΔS^o) were estimated. Positive values of the ΔH^o and ΔS^o at low temperature region may indicate the lack of the interaction with the stationary phase ligands. A possible retention mechanism at different temperatures for C60 and C70 molecules has been discussed.     

Mechanistic study of the oxidation of N-phenyldiethanolamine by <Emphasis Type="Italic">bis</Emphasis>(hydrogen periodato)argentate(III) complex anion

The kinetics of oxidation of phenyldiethanolamine (PEA) by a silver(III) complex anion, [Ag(HIO₆)₂]⁵⁻, has been studied in an aqueous alkaline medium by conventional spectrophotometry. The main oxidation product of PEA has been identified as formaldehyde. In the temperature range 20.0–40.0 °C , through analyzing influences of [OH⁻] and [IO ₄ ⁻ ]_tot on the reaction, it is pseudo-first-order in Ag(III) disappearance with a rate expression: k _obsd = (k ₁ + k ₂[OH⁻]) K ₁ K ₂[PEA]/{f([OH⁻])[IO ₄ ⁻ ]_tot + K ₁ + K ₁ K ₂ [PEA]}, where k ₁ = (0.61 ± 0.02) × 10⁻² s⁻¹, k₂ = (0.049 ± 0.002) M⁻¹ s⁻¹ at 25.0 °C and ionic strength of 0.30 M. Activation parameters associated with k ₁ and k ₂ have also been derived. A reaction mechanism is proposed involving two pre-equilibria, leading to formation of an Ag(III)-periodato-PEA ternary complex. The ternary complex undergoes a two-electron transfer from the coordination PEA to the metal center via two parallel pathways: one pathway is spontaneous and the other is assisted by a hydroxide ion.     

Kinetics of thermal decomposition of dinitramide

Kinetic regularities of thermal decomposition of dinitramide in aqueous and sulfuric acid solutions were studied in a wide temperature range. The rate of the thermal decomposition of dinitramide was established to be determined by the rates of decomposition of different forms of dinitramide as the acidity of the medium increases: first, N(NO₂)⁻ anions, then HN(NO₂)₂ molecules, and finally, protonated H₂N(NO₂)₂ ⁺ cations. The temperature dependences of the rate constants of the decomposition of N(NO₂)⁻ (k _an) and HN(NO₂)₂ (k′_ac) and the equilibrium constant of dissociation of HN(NO₂)₂ (K _a) were determined:k _an=1.7·10¹⁷ exp(−20.5·10³/T), s⁻¹,k′_ac=7.9·10¹⁶ exp(−16.1·10³/T), s⁻¹, andK _a=1.4·10 exp(−2.6·10³/T). The temperature dependences of the decomposition rate constant of H₂N(NO₂)₂ ⁺ (k _d) and the equilibrium constant of the dissociation of H₂N(NO₂)₂ ⁺ (K _d) were estimated:k _d=10¹² exp(−7.9·10³/T), s⁻¹ andK _d=1.1 exp(6.4·10³/T). The kinetic and thermodynamic constants obtained make it possible to calculate the decomposition rate of dinitramide solutions in a wide range of temperatures and acidities of the medium. In this series of articles, we report the results of studies of the thermal decomposition of dinitramide performed in 1974–1978 and not published previously. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 2129–2133, December, 1997.     

Thermal decomposition of complexes of cadmium(II) and mercury(II) with triphenylphosphanes

A series of substituted triphenylphosphane complexes of the type CdL₂X₂ (L= triorthotolylphosphane or trimetatolylphosphane; X=Cl⁻, Br⁻ or I⁻) and HgL₂X₂ (L=triphenylphosphane or triorthotolylphosphane) was prepared fresh. The thermal decomposition was carried out in air with heating rate programmed at 10°C min⁻¹ and it revealed that the complexes with ortho derivative were less stable and the triphenylphosphane moiety leaves along with halogen in the first step. All the complexes were stable up to 210°C. However, the stability order of the tetrahedral complexes was X=Cl>Br. Values of n, E, lnA and ΔS ^# have been approximated and compared. Complexes having Br have higher E _a, lnA and ΔS ^# values than that having Cl.     

Study of mechanism retention of nonvolatile alkylphosphonic acids on unmodified selected polymer-based ion exchanger columns

The retention of alkylphosphonic acids (MPA, EPA, PPA, and BPA) and inorganic anions (Cl⁻, NO₃⁻, and SO₄²⁻) were studied on two anion exchangers, e.g., Dionex IonPac AS4A-SC (250 ± 4 mm I.D.) and Satisfaction P 4000-SAX (50 ± 4.6 mm I.D.) under isocratic elution conditions with evaporative light scattering detector. The plots of retention factors, k, of organic anions vs. the reciprocal of eluent ion concentration show good linearity. The major retention mechanisms are interpreted as ion exchange and some others interactions. The C effect of organic modifier added to the aqueous buffered mobile phase is also investigated.     

Comparative study on uni-univalent and uni-bivalent ion-exchange reaction on Doulite A-116

Determination of ion-exchange equilibrium constant (K) for Cl⁻/I⁻ and Cl⁻/C₂O₄²⁻ system was studied at different temperatures from 25 to 45°C and by varying concentration of iodide and oxalate ion solution. For both uni-univalent and uni-bivalent exchange systems, using 0.5 g of ion-exchange resin DUOLITE A-116 (in chloride form), the value of K increases with rise in temperature i.e., from 13.0 at 25°C to 19.05 at 45°C for Cl⁻/I⁻ system and 33.0 at 25°C to 63.0 at 45°C for Cl⁻/C₂O₄²⁻ system indicating the endothermic ion-exchange reaction. The difference in K values at the same temperature for the two was related to the ionic charge of exchangeable ions in the solution.     

Reactivity trends in the base hydrolysis of 6-nitro-2H-chromen-2-one and 6-nitro-2H-chromen-2-one-3-carboxylic acid in binary mixtures of water with methanol and acetone at different temperatures

Kinetics of the base hydrolysis of 6-nitro-2H-chromen-2-one (NC) and 6-nitro-2H-chromen-2-one-3-carboxylic acid (NCC) in water-methanol and water-acetone mixtures was studied at temperature range from 283 to 313 K. The activation parameters of the reactions were evaluated and discussed. The change in the activation barrier of the investigated compounds from water to water-methanol and water-acetone mixtures were estimated from the kinetic data. The base hydrolysis of NC and NCC in the water-methanol and water-acetone mixtures follows a rate law with k _obs = k ₂[OH⁻] and k _obs = k ₁ + k ₂[OH⁻], respectively. The decrease in the rate constants of NC and NCC hydrolysis, as the proportion of methanol and acetone increases, is accounted for by the destabilization of the OH⁻ ion. The activation and thermodynamic parameters were determined.     

Determination of the rate constants for the reaction Fe + O<Subscript>2</Subscript> = FeO + O in the forward and reverse directions

The results of our experimental studies and an analysis of the published data on the rate constant for the reaction Fe + O₂ = FeO + O in the forward (I) and reverse (−I) direction are reported. The data obtained in this work are described by the expressions k ₁ = 6.2 × 10¹⁴exp(−11100 K/T) cm³ mol⁻¹ s⁻¹ and k ₋₁ = 6.0 × 10¹³exp(−588 K/T) cm³ mol⁻¹ s⁻¹ (T = 1500–2500 K). The generalized expressions for the temperature dependences of these rate constants derived by combining our results with the literature data can be presented as k ₁ = 9.4 × 10¹⁴(T/1000)^0.022exp(−11224 K/T) cm³ mol⁻¹ s⁻¹ (T = 1500–2500 K) and k ₋₁ = 1.8 × 10¹⁴(1000/T)^0.37exp(−367 K/T) cm³ mol⁻¹ s⁻¹ (T = 200–2500 K).     

Ligand Exchange Processes on Solvated Lithium Cations. II. Complexation by Cryptands in γ-Butyrolactone as Solvent

Kinetic studies on Li⁺ exchange between the cryptands C222 and C221, and γ-butyrolactone as solvent were performed as a function of ligand-to-metal ratio, temperature and pressure using ⁷Li NMR. The thermal rate and activation parameters are: C222: k ₂₉₈ = (3.3 ± 0.8)×10⁴ M⁻¹ s⁻¹, ΔH ^# = 35 ± 1 kJ mol⁻¹ and ΔS ^# = −41 ± 3 J K⁻¹ mol⁻¹; C221: k ₂₉₈ = 105 ± 32 M⁻¹ s⁻¹, ΔH ^# = 48 ± 1 kJ mol⁻¹ and ΔS ^# = −45 ± 2 J K⁻¹ mol⁻¹. Temperature and pressure dependence measurements were performed in the presence of an excess of Li⁺. The influence of pressure on the exchange rate is insignificant for both ligands, such that the value of activation volume is around zero within the experimental error limits. The activation parameters obtained in this study indicate that the exchange of Li⁺ between solvated and chelated Li⁺ ions follows an associative interchange mechanism. Electronic Supplementary Material Supplementary material is available to authorised users in the online version of this article at . For Part I see: R. Puchta, M. Galle, N.J.R. van Hommes, E. Pasgreta and R. van Eldik: Inorg. Chem. 43, 8227 (2004).     

Kinetics of oxidation of <Emphasis Type="Italic">N</Emphasis>,<Emphasis Type="Italic">N</Emphasis>′-ethylenebis(isonitrosoacetylacetoneimine)copper(II) by peroxydisulfate in aqueous acidic solutions

Peroxydisulfate (PDS) oxidizes N,N′-ethylenebis(isonitrosoacetyleacetoneimine)copper(II) complex, Cu^IIL, to the corresponding copper(III) complex, [Cu^IIIL]⁺. The kinetic runs were performed in the presence of EDTA to scavenge any trace metal impurities. The kinetics of the reaction at constant pH, ionic strength, and temperature obeys the rate law d[Cu^IIIL]/dt = 2k ₂[Cu^IIL][S₂O₈ ²⁻] with k ₂ having a value of (8.85 ± 0.32) × 10⁻² M⁻¹ s⁻¹ at μ = 0.30 M and T = 25.0 °C. The rate constant k ₂ is not affected by variation of pH over the range 3.60–5.20. The second order rate constant is also unaffected by changing ionic strength. The values of k _obs were determined over the temperature 25.0–40.0 °C range. The enthalpy of activation, ∆H*, and entropy of activation, ∆S*, have been calculated as 34.9 ± 0.5 kJ mol⁻¹ and −173.3 ± 11.4 J K⁻¹ mol⁻¹, respectively. The kinetics of this reaction, as far as we know, is the first evidence that copper(III) is the likely reactive species in copper catalyzed PDS oxidation reactions.     

Study of temperature effect on uni-univalent and uni-bivalent ion exchange reaction

Ion exchange equilibrium constant (K) for Cl⁻/Br⁻ and Cl⁻/C₂O₄²⁻ system was studied at different temperatures from 30 to 45°C. For both uni-univalent and uni-bivalent exchange systems, the value of K increases with rise in temperature i.e., from 1.16 at 30°C to 2.95 at 45°C for Cl⁻/Br⁻ system and 19.5 at 30°C to 30.0 at 45°C for Cl⁻/C₂O₄²⁻ system indicating the endothermic ion exchange reaction. The difference in K values at the same temperature for the two was related to the ionic charge of exchangeable ions in the solution. The article is published in the original.     

Kinetics and mechanism of oxidation of <Emphasis Type="Italic">N</Emphasis>-methylethylamine by bis(hydrogenperiodato)argentate(III) complex anion

Oxidation of N-methylethylamine by bis(hydrogenperiodato)argentate(III) ([Ag(HIO₆)₂]⁵⁻) in alkaline medium results in demethylation, giving rise to formaldehyde and ethylamine as the oxidation products. The oxidation kinetics has been followed spectrophotometrically in the temperature range of 20.0–35.0 °C, and shows an overall second-order character: being first-order with respect to both Ag(III) and N-methylethylamine. The observed second-order rate constants k′ increase with increasing [OH⁻] of the reaction medium, but decrease with increasing the total concentration of periodate. An empirical rate expression for k′ has been derived as: k′ = (k _a + k _b[OH⁻])K ₁/{f([OH⁻])[IO₄ ⁻]_tot + K ₁}, where k _a and k _b are rate parameters, and K ₁ is an equilibrium constant. These parameters have been evaluated at all the temperatures studied, enabling calculation of activation parameters. A reaction mechanism is suggested to involve two pre-equilibria, leading to formation of an intermediate Ag(III) complex, namely [Ag(HIO₆)(OH)(MeNHEt)]²⁻. In the subsequent rate-determining steps, this intermediate undergoes inner-sphere electron transfer from the coordinated amine to the metal center via two distinct routes, one of which is spontaneous while the other is mediated by a hydroxide ion.     

Kinetics of the ?OH-radical initiated reactions of acetic acid and its deuterated isomers

Kinetics of the ^•OH-initiated reactions of acetic acid and its deuterated isomers have been investigated performing simulation chamber experiments at T = 300 ± 2 K. The following rate constant values have been obtained (± 1σ, in cm³ molecule⁻¹ s⁻¹): k ₁(CH₃C(O)OH + ^•OH) = (6.3 ± 0.9) × 10⁻¹³, k ₂(CH₃C(O)OD + ^•OH) = (1.5 ± 0.3) × 10⁻¹³, k ₃(CD₃C(O)OH + ^•OH) = (6.3 ± 0.9) × 10⁻¹³, and k ₄(CD₃C(O)OD + ^•OH) = (0.90 ± 0.1) × 10⁻¹³. This study presents the first data on k ₂(CH₃C(O)OD + ^•OH). Glyoxylic acid has been detected among the products confirming the fate of the ^•CH₂C(O)OH radical as suggested by recent theoretical studies.     

A kinetic analysis of thermal decomposition of polyaniline/ZrO<Subscript>2</Subscript> composite

Synthesis, characterization and thermal analysis of polyaniline (PANI)/ZrO₂ composite and PANI was reported in our early work. In this present, the kinetic analysis of decomposition process for these two materials was performed under non-isothermal conditions. The activation energies were calculated through Friedman and Ozawa-Flynn-Wall methods, and the possible kinetic model functions have been estimated through the multiple linear regression method. The results show that the kinetic models for the decomposition process of PANI/ZrO₂ composite and PANI are all D₃, and the corresponding function is ƒ(α)=1.5(1−α)^2/3[1−(1-α)^1/3]−1. The correlated kinetic parameters are E _a=112.7±9.2 kJ mol⁻¹, lnA=13.9 and E _a=81.8±5.6 kJ mol⁻¹, lnA=8.8 for PANI/ZrO₂ composite and PANI, respectively.     

Kinetics and mechanism of the acid-catalysed hydrolysis of the carbonatotetraimidazolecobalt(III) ion

Summary The kinetics of the acid-catalysed hydrolysis of the [(imidazole)₄Co(CO₃)]⁺ ion was found to follow the rate law -dln[complex]/dt = k ₁ K[H⁺](1 + K[H ⁺]) in the 25–45 °C range, [H⁺] 0.05–1.0 m range and I = 1.0m. The reaction sequence consists of a rapid protonation equilibrium followed by the one-end dissociation of the coordinated carbonato ligand (rate-determining step) and subsequent fast release of the monodentate carbonato ligand. The rate parameter values, k ₁ and ITK, at 25 °C are 6.48 × 10⁻³s⁻¹ and 0.31m ⁻¹, respectively, and activation parameters for k ₁ are ΔH ₁ ^≠ = 86.1 ± 1.2kJ mol⁻¹ and ΔS ₁ ^≠ = 2.1 ± 6.3 J mol⁻¹K⁻¹. The hydrolysis rate increases with increase in ionic strength. The different ways of dealing with the data fit are presented and discussed. The kinetic results are compared with those for the similar cobalt(III) complexes.