Comparative kinetic analysis on thermal degradation of some cephalosporins using TG and DSC data

Chemistry Central Journal

Adriana Fuliaş³  Gabriela Vlase¹  Titus Vlase¹  Codruţa Soica³  Alina Heghes³  Marius Craina²  Ionuţ Ledeti³ 

[1] West University of Timişoara, Research Centre for Thermal Analysis in Environmental Problems, Pestalozzi Street 16, Timişoara, RO-300115, ROMÂNIA

[2] University of Medicine and Pharmacy “Victor Babeş”, Faculty of Medicine, Eftimie Murgu Square 2, Timişoara, RO-300041, ROMÂNIA

[3] University of Medicine and Pharmacy “Victor Babeş”, Faculty of Pharmacy, Eftimie Murgu Square 2, Timişoara, RO-300041, ROMÂNIA

关键词: NPK method;    DSC;    TG/DTG;    Non-isothermal conditions;    Kinetic parameters;    Cephalosporin;   

Others  :  787923
DOI  :  10.1186/1752-153X-7-70

 received in 2013-01-04, accepted in 2013-02-26,  发布年份 2013

【 摘 要 】

Background

The thermal decomposition of cephalexine, cefadroxil and cefoperazone under non-isothermal conditions using the TG, respectively DSC methods, was studied. In case of TG, a hyphenated technique, including EGA, was used.

Results

The kinetic analysis was performed using the TG and DSC data in air for the first step of cephalosporin’s decomposition at four heating rates. The both TG and DSC data were processed according to an appropriate strategy to the following kinetic methods: Kissinger-Akahira-Sunose, Friedman, and NPK, in order to obtain realistic kinetic parameters, even if the decomposition process is a complex one.

The EGA data offer some valuable indications about a possible decomposition mechanism. The obtained data indicate a rather good agreement between the activation energy’s values obtained by different methods, whereas the EGA data and the chemical structures give a possible explanation of the observed differences on the thermal stability. A complete kinetic analysis needs a data processing strategy using two or more methods, but the kinetic methods must also be applied to the different types of experimental data (TG and DSC).

Conclusion

The simultaneous use of DSC and TG data for the kinetic analysis coupled with evolved gas analysis (EGA) provided us a more complete picture of the degradation of the three cephalosporins. It was possible to estimate kinetic parameters by using three different kinetic methods and this allowed us to compare the E_a values obtained from different experimental data, TG and DSC. The thermodegradation being a complex process, the both differential and integral methods based on the single step hypothesis are inadequate for obtaining believable kinetic parameters. Only the modified NPK method allowed an objective separation of the temperature, respective conversion influence on the reaction rate and in the same time to ascertain the existence of two simultaneous steps.

【 授权许可】

   
2013 Fuliaş et al.; licensee Chemistry Central Ltd.

【 图 表 】

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