Martin Tjahjono

Three approaches to total quantitative phase analysis of organic mixtures using an external standard

Three different approaches for a total quantitative phase analysis of organic mixture data were presented and subsequently tested on a set of ten ternary powder mixtures consisting of α-glycine, α-lactose monohydrate and paracetamol form I. In each of these methods, an external standard was used (in the present study, diamond) to determine the diffractometer constant, which was employed to place the crystalline intensities of all other samples on an absolute scale. In Method A, pure component diffractograms were also measured. In Methods B and C, no pure component diffractograms were used. Using Methods A–C, both the absolute crystalline compositions and all the amorphous compositions of the samples were determined. These methods outperform the quantitative phase analysis provided by conventional Rietveld analysis. An average error of less than 0.5 wt% was achieved with the present approaches, whereas the average error from conventional Rietveld analysis was ca 1.3 wt%.

Combined on-line transmission FTIR measurements and BTEM analysis for the kinetic study of a consecutive reaction in aqueous–organic phase medium

Combined on-line transmission FTIR spectroscopy and band-target entropy minimization (BTEM) analysis were employed in order to monitor and analyze the kinetics of the alkaline hydrolysis reaction of diethyl phthalate (DEP) in aqueous-ethanol solvent mixture. This reaction is irreversible and involves two consecutive steps with the formation of the observable mono-ion intermediate species. The pure component mid-FTIR spectra of the reactive species involved in this reaction, namely DEP, mono-ion intermediate and di-ion product were successfully reconstructed using BTEM. Their corresponding concentrations were also calculated and subsequently employed to derive the kinetic rate parameters. The effect of temperature and the solvent mixture compositions on these two consecutive reaction steps were also discussed. The temperature variation study showed that both reaction rate coefficients increased with temperature. Both rate coefficients were also affected by the solvent mixture compositions and reached minimum values at certain water-ethanol solvent composition (circa 60% (v/v)). This study shows the utility of combined on-line transmission FTIR spectroscopy and chemometric techniques for the present, rather complex, consecutive organic reaction. Moreover, the present type of approach could facilitate better understanding of a wide variety of organic reactions that are performed in aqueous and mixed aqueous-organic solvents.

Combined online spectroscopic, calorimetric, and chemometric analysis: reaction enthalpy determinations in single and parallel reactions.

Calorimetry and signal processing: Vibrational spectroscopies, heat-flow microcalorimetry, and multivariate analysis are combined to decouple the reaction enthalpies of parallel reactions [picture: see text]. This methodology allows the evaluation of reaction enthalpy from complex systems without recourse to conventional kinetic modeling. Simultaneous in situ/online spectroscopy and heat-flow measurements as well as multivariate analyses are performed, apparently for the first time, to determine heats of reaction for single and parallel reactions. Two different vibrational spectroscopy techniques, namely Raman and FTIR spectroscopy, are used in conjunction with flow-through TAM III microcalorimetry. With respect to the spectroscopic analysis, the reaction spectra are first analyzed to determine the pure-component spectra and the corresponding concentrations without recourse to external calibration. With respect to the calorimetric analysis, a soft modeling approach is employed to determine the heats of reaction without recourse to any conventional kinetic models. This combined approach is implemented to determine the extents of reaction as well as the corresponding heats of reaction at 298.15 K and 0.1 MPa for a) the hydrolysis of acetic anhydride (single reaction) and b) the hydrolysis of methyl paraben and ethyl paraben in alkaline solution (both single and parallel reactions). In the latter case, the heat-flow contributions from the two simultaneous reactions are successfully decoupled. Taken together, these results demonstrate proof of concept for the present approach. The newly developed methodology appears to be quite general and particularly useful for investigating complex reaction systems. This is particularly true for multiple simultaneous reactions and reactions where the detailed kinetic expressions are not available, or cannot be easily determined. The use of extents of reaction is also very helpful where there is high variability in reaction rates, that is, due to the presence of impurities, changes in catalyst activity, or concentrations, temperature, and pH.

Kinetic study of a complex triangular reaction system in alkaline aqueous-ethanol medium using on-line transmission FTIR spectroscopy and BTEM analysis.

The kinetics of the base-catalyzed reaction of methyl 4-hydroxybenzoate in aqueous-ethanol solvent medium was studied and analyzed via combined on-line transmission FTIR spectroscopy and Band-Target Entropy Minimization (BTEM) technique. This reaction is considered complex since it involves simultaneous hydrolysis and ethanolysis reactions of methyl 4-hydrozybenzoate (MP) to form ethyl 4-hydroxybenzoate (EP) as an intermediate and sodium 4-hydroxybenzoate as a final product. The pure component spectra of the reactive species involved in the reaction were reconstructed using BTEM technique. Their corresponding real concentrations were calculated and subsequently used for analyzing the kinetics of this triangular reaction system. The effects of temperature and solvent mixture compositions were studied. In general, the results show that the rates of both hydrolysis and ethanolysis reactions increase with temperature. Addition of ethanol to the solvent mixture also reduces the rates of the hydrolysis reactions. The effect of solvent mixture on the rate of ethanolysis reaction is more complex and influenced by at least two competing factors, namely the concentration of ethoxide ion in the solution and the stabilization effect on the reactant. The enthalpy and entropy activation parameters, ΔH(‡) and ΔS(‡), of both the hydrolysis and ethanolysis reactions were determined using the Eyring equation and the activation parameters confirm the associative nature in the elementary steps in these reactions. Finally, it is shown that the dominant synthetic pathway in this triangular system changes from direct hydrolysis of methyl 4-hydrozybenzoate to the indirect pathway via ethanolysis and then hydrolysis depending on the solvent mixture composition.

A multicomponent calibration approach to the microabsorption problem involving inorganic mixtures

Microabsorption may present a serious obstacle to performing accurate quantitative phase analysis by the Rietveld method for samples that contain phases with high X-ray absorption contrast. In this study, a multicomponent calibration approach is introduced to reduce the systematic bias that is not accounted for in conventional Rietveld analysis. In order to demonstrate this approach, six ternary inorganic mixtures containing components with diverse mass absorption coefficients were prepared. Two of the six mixtures were chosen as a calibration set to obtain the corresponding calibration parameters. These parameters were used to predict accurately the compositions of the remaining mixtures. Additionally, several other issues concerning sample preparation, the choice of the calibration set and the inclusion of complimentary techniques to determine the calibration parameters are addressed. The present approach offers practical advantages over the frequently used Brindley method, since it does not require any additional information concerning particle size and morphology.