Non-parametric Kinetics Method Research Articles

Thermal behaviour and kinetic study of some triazoles as potential anti-inflammatory agents

Thermogravimetric (TG), differential thermogravimetric analysis and differential scanning calorimetry had been used to characterize the thermal stability of four new heterocyclic compounds with triazolic structure. The four analysed compounds have similar thermal behaviours, namely the thermal mal curves of these new compounds show three thermal events. These compounds were thermally stable up to 110 °C. Above this temperature, the evolution of hydrochloric acid took place as observed by EGA. Identification and the monitoring of gaseous species released during thermal decomposition of pure triazoles in air atmosphere have been carried out by coupled TG–FTIR. Between 110 and 220 °C the main gaseous product is HCl which was identified on the basis of these FTIR spectra. Arguments for a rapid thermooxidation of the four molecules were brought by EGA by identifying the substances which arise from both the destruction of side chains and of triazolic ring. The kinetic analysis of the destruction process of triazolic structure was investigated using the TG data in air for the substance’s decomposition in non-isothermal conditions. The isoconversional methods, Kissinger–Akahira–Sunose, Flynn–Wall–Ozawa and Friedman, were applied to determine the activation energy from the analysis of four curves measured at different heating rates. In order to obtain realistic kinetic parameters, even if the decomposition process is a complex one, the non-parametric kinetics method was also used. A good agreement between the data obtained from the four applied methods was found.

Non‐parametric kinetic analysis of the oxidation of TiN and TiC nanoparticles

AbstractThe non‐parametric kinetics (NPK) method was developed for simulation purposes by applying macroscopic kinetics to complex reactions and transformations. This is able to describe a reaction and provide information about its temperature function, such as Arrhenius equation, and the type of reaction involved. To determine whether the method is applicable to reactions involving nanoscale materials, the NPK method is applied to study the oxidation of titanium nitride and carbide and the results are compared with those already obtained. NPK reproduces both reactions without any problems. It provides consistent results in the case of nitride, but in the case of carbide it suggests that more transformations are involved in the reaction, most likely including diffusional control of the reaction. © 2011 Wiley Periodicals, Inc. Int J Chem Kinet 44: 147–154, 2012

Analysis of the relative strength of the singular values obtained from the non-parametric kinetic method

The non-parametric kinetic method (NPK) is a method for the processing of thermoanalytical data, which does not make any assumption about the functionality of the reaction rate with the degree of conversion or with the temperature. This method has not been widely used due to its mathematical sophistication and difficulty of automation. The original NPK method uses only the first (maximum) singular value whereas additional information could be drawn from the remaining singular values. A hypothetical application of the NPK, which uses all the significant singular values (modified version of the NPK), is the separation of two or more steps of a complex decomposition reaction. Using simulated data, we have demonstrated that the modified version of the NPK is not useful to discriminate among the decomposition steps of a consecutive complex decomposition reaction scheme. Nevertheless, the analysis of the relative strength of the singular values is useful to assess the degree of separability of the temperature and conversion functions, which are the outcome of the NPK. Taking into account the relative magnitude of the first singular value with regard to the remaining singular values, we have proposed an automated two-scan version of the NPK method which guarantees two separable functions. As the separability of both temperature and conversion functions is the imperative assumption of the single-step kinetics approximation, the two-scan NPK method can be used as a testing method for those methods based on this approximation, the model-free and model-fitting methods.

Thermal behaviour of cephalexin in different mixtures

Abstract The thermoanalytical curves (TA), i.e. TG, DTG and DTA for pure cephalexin and its mixtures with talc, magnesium stearate, starch and microcrystalline cellulose, respectively, were drawn up in air and nitrogen at a heating rate of 10 °C min−1. The thermal degradation was discussed on the basis of EGA data obtained for a heating rate of 20 °C min−1. Until 250 °C, the TA curves are similar for all mixtures, up this some peculiarities depending on the additive appears. These certify that between the pure cephalosporin and the excipients do not exists any interaction until 250 °C. A kinetic analysis was performed using the TG/DTG data in air for the first step of cephalexin decomposition at four heating rates: 5, 7, 10 and 12 °C min−1. The data processing strategy was based on a differential method (Friedman), an integral method (Flynn–Wall–Ozawa) and a nonparametric kinetic method (NPK). This last one allowed an intrinsic separation of the temperature, respective conversion dependence on the reacti...

TG, EGA and kinetic study by non-isothermal decomposition of a polyaniline with different dispersion degree

Polyaniline was obtained by oxidizing aniline in hydrochloric acid media with ammonium peroxidisulfate as oxidizing agent. Molar ratio aniline/oxidant was 1 and ani- line/acid ratio: ,a t-5 and 400 C, respectively, 800 mL water. The both compounds were studied using two different experimental strategies: the coupled TG-EGA (FTIR) tech- nique by decomposition in dynamic air atmosphere and the kinetic analysis of TG data obtained at four heating rates (5, 7, 10 and 15 K min -1 ). The kinetic analysis of the TG non-isothermal data was performed with the Flynn-Wall- Ozawa, Friedman's, and modified non-parametric kinetic (NPK) methods. By means of the coupled techniques spec- troscopic arguments on the reaction mechanism were obtained, i.e. the oxidative degradation of the quinoine ring as the first step. The values of the activation energy by the three used methods are in good agreements. According to the NPK method, the termodegradation process consist in physical (diffusion) and chemical steps.

Thermal behaviour of some industrial and food dyes

Thermal behavior of four food dyes, i.e. tartrazine, crysoine, azorubine and amarant was studied under non-isothermal conditions, in dynamic air atmosphere and at heating rates of 5, 10, 15 and 20°C min–1. The TG data were correlated to the FTIR spectra of each sample, before and after the thermal decomposition. Kinetic study by processing the TG data was performed. The main conclusion of this study is that the non-parametric kinetic method allows a separation of the steps of a complex process and that the values of the activation energy obtained by this method agree satisfactory with that of Flynn–Wall–Ozawa estimation.

A kinetic study of the thermal degradation of ammonium species inside a 3D zincophosphate

Ammonium ions remain inside the 3D zincophosphate framework after the hydrothermal crystallization. These species in co-operation with sodium cations exert a specific templating role in the formation of the open-framework lattice. The decomposition of the ammonium species under non-isothermal conditions has been studied by the non-parametric kinetics (NPK) method. The process is characterized by a complex kinetic mechanism and a relatively high activation energy for the main reaction step, E a = 336 kJ/mol. These reflect the fact that the decomposition of the ammonium ions inside the zincophosphate framework involves not only the diffusion of the liberated species through the narrow channels of the microporous framework but also a prior overcoming of strong electrostatic interactions and the breaking of hydrogen bonds.

Thermal stability of food additives of glutamate and benzoate type

Many years ago, thermal analysis earned its place as a current instrumentation technique in assisting/solving the analytical problems of pharmaceuticals. A relative new trend is the study of the thermal stability of food additives in connection with the molecular structure. The studied compounds were: natrium and potassium glutamate, respectively natrium, potassium and calcium benzoate. The thermogravimetric data (TG) were obtained in dynamic nitrogen atmosphere, with open Pt crucible and heating rates of 5, 7, 10 and 12 K min-1, using a Perkin-Elmer TGA7 equipment. In order to estimate the non-isothermal kinetic parameters, the Friedman's differential-isoconversional method and the method suggested by Budrugeac and Segal (based on the compensation effect) were used. A variation of the activation energy vs. conversion was observed by using Friedman's method. The discrimination between the different reaction steps was performed by the non-parametric kinetic method, suggested by Sempere, Nomen and Serra. This is due to a complex process. The thermal stability data are very important for avoiding a possible misuse by processing of the studied food additives.

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Due to the criticism of the non-isothermal kinetic at a single heating rate, in the last period, data obtained at different heating rates are processed by means of elevated methods like Friedman’s (FD) differential-isoconversional method or the one suggested by Budrugeac and Segal (BS). The non-parametric kinetics (NPK) method, suggested by Serra, Nomen and Sempere offers two major advantages: the possibility of separation of two or more steps of a complex decomposition reaction; and the possibility of discrimination between the conversion, with regard to the temperature functions of a rate equation. Comparative data of FD, BS and modified version of NPK method are presented for decomposition of three compounds used as polyisocyanate stabilizer.

Kinetics of thermal decomposition of alkaline phosphates

Summary The thermal behavior of KH2PO4, NaH2PO4 and Na2HPO4 under non-isothermal conditions using TG method with different heating rates was studied. The values of the reaction rate were processed by means of Friedman’s differential-isoconversional method. A dependence of the activation energy vs. conversion was observed. Therefore a procedure based on the compensation effect (suggested by Budrugeac and Segal) was applied. A less speculative data processing protocol was offered by the non-parametric kinetics method suggested by Serra, Nomen and Sempere. Three steps were observed by non-isothermal heating: a dehydration, a dimerization and a polycondensation. The differences in the intimate reaction mechanism are determined by the initial number of water molecules.

“Model-free” kinetic analysis?

All kinetic analyses aim to determine a sufficient number of kinetic parameters, usually at least an apparent Arrhenius activation energy and pre-exponential factor, and a conversion function or kinetic model (making up a ‘kinetic triplet’), so that accurate extrapolations of kinetic behaviour can be made. “Model-free” methods of kinetic analysis postpone the problem of identifying a suitable kinetic model until an estimate of the activation energy has been made. A major reason for doing this is that misidentification of the kinetic model has a marked effect on the values obtained for the Arrhenius parameters in both isothermal and non-isothermal kinetic analyses. Some aspects of this problem are discussed. The non-parametric kinetics (NPK) method [1,2] is a “model-free” method of kinetic analysis that does not seem to have received the attention that it deserves. This is probably because of its mathematical sophistication and the fact that the matrix and non-linear regression calculations involved are not readily automated. The principle of the method appears to be that of “forcing” a set of non-isothermal data into the set which should have been obtained if the experiments had been carried out isothermally. The method deserves wider testing and also raises some interesting aspects of the philosophy behind non-isothermal kinetic analysis.

Progress in Non-parametric Kinetics

The non-parametric kinetics (NPK) method has been recently developed for the kinetic treatment of thermoanalytical data. The most significant feature of this method is its ability to provide information about the reaction kinetics without any assumptions either about the functionality of the reaction rate with the degree of conversion or the temperature. This paper presents the results of the application of the method to adiabatic calorimetry. Some data have been obtained by numerical simulation, but also the thermal decomposition of DTBP, a well known first order reaction, has been studied, being the obtained results in good agreement with literature.

A new method for the kinetic study of thermoanalytical data:: The non-parametric kinetics method

A new method, called non-parametric kinetics (NPK), for the treatment of non-isothermal thermoanalytical data has been developed. The most significant feature of this method is its ability to provide a kinetic model that fits the experimental data, without any assumptions either about the functionality of the reaction rate with the degree of conversion or the temperature. The thermal decomposition of dibenzoyl peroxide has been studied in order to validate the NPK method, and the results are compared with those of the traditional ones.

Population pharmacokinetics and pharmacodynamics: potential use for gathering dose-concentration-response.

The population approach is a general term covering different aspects of kinetic and dynamic data collected mainly from drug-treated patients and new techniques allowing evaluation of sparse observations from each subject. Such data originate from clinically relevant conditions and can give information on several qualities of a drug. An example is given with the tricyclic antidepressant nortriptyline for which the kinetics and the concentration-effect relationship have been thoroughly documented previously with conventional techniques. We have evaluated retrospective data from a therapeutic drug monitoring service using a nonparametric population kinetic method (NPML) that allows description of kinetic outliers and nonlinear relationships between kinetic parameters and covariates. In addition, drug interactions, nonlinear kinetics and dosing habits were studied with other techniques corroborating previous results and adding new information. The concentration-effect relationship could not be evaluated from our data as information on efficacy and adverse effects was of too low quality. However, several controlled studies have defined a therapeutic concentration interval and a discussion on dosing strategies is based on this interval. Collection of sparse data in patients during phases II-IV of drug development as a complement to conventional studies is highly recommendable.