Advancement in optimization tactic achieved by newly developed chromatographic response function: application to LC separation of raloxifene and its impurities

In this paper a new chromatographic response function (CRF) is designed and proposed for utilization in the optimization strategies. The function capability to represent the overall quality of a experimentally obtained chromatograms was compared to the other two objective functions and proved to give more accurate and reliable results. The new CRF has improved concept of separation and time term estimation. It reflects all important defects of the chromatogram such as the appearance of asymmetrical or overlapping peaks and prolonged elution time and allows the appropriate weighting of each of them. The LC separation of raloxifene and its four impurities was evaluated through the central composite design experimental plan choosing the new CRF to be the only output of the system. The function demonstrated the ability to judge the impact of the complex interactions of the selected chromatographic parameters (acetonitrile content in the mobile phase, sodium dodecyl sulfate concentration in the water phase, pH of the mobile phase and column temperature) on the mixture behavior and led to the determination of the optimal separation conditions. The newly developed CRF proved to have the advanced performances and it presents the important step forward in the optimization of the chromatographic separation.     

Synthesis and cationic ring-opening polymerization of mono- and bifunctional spiro orthoesters containing ester groups and depolymerization of the obtained polymers: An approach to chemical recycling for polyesters as a model system

A spiro orthoester having an ester moiety, 2-acetoxymethyl-1,4,6-trioxaspiro[4.6]undecane (4) was synthesized, and its cationic polymerization and depolymerization of the obtained polymer (5) were carried out. The monomer 4 underwent cationic polymerization with a cationic catalyst to afford the corresponding poly(cyclic orthoester) 5. The obtained polymer 5 could be depolymerized with a cationic catalyst to regenerate the monomer 4 in an excellent yield. Further, bifunctional spiro orthoesters (6, 8, 9) having diester moieties were synthesized from terephthalic acid, succinic acid, and 1,4-cyclohexanedicarboxylic acid, and their acid-catalyzed reversible crosslinking–decrosslinking was examined. The bifunctional monomer 6 derived from terephthalic acid underwent cationic crosslinking to afford the corresponding network polymer (7), which could be also depolymerized to regenerate the original bifunctional monomer 6. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 2551–2558, 1999     

Thermal analysis applied to the characterization of degradation in soil of polylactide: II. On the thermal stability and thermal decomposition kinetics

The disposal stage of polylactide (PLA) was assessed by burying it in active soil following an international standard. Degradation in soil promotes physical and chemical changes in the polylactide properties. The characterization of the extent of degradation underwent by PLA was carried out by using Thermal Analysis techniques. In this paper, studies on the thermal stability and the thermal decomposition kinetics were performed in order to assess the degradation process of a commercial PLA submitted to an accelerated soil burial test by means of multi-linear-non-isothermal thermogravimetric analyses. Results have been correlated to changes in molecular weight, showing the same evolution as that described by the parameters of thermal stability temperatures and apparent activation energies. The decomposition reactions can be described by two competitive different mechanisms: Nucleation model (A2) and Reaction Contracting Volume model (R3). The changes in the kinetic parameters and kinetic models are in agreement with the calorimetric and dynamic-mechanical-thermal results, presented in the Part I of the study [1].     

Effect of sample size on isothermal crystallization measurements performed in a differential scanning calorimeter: A method to determine avrami parameters without sample thickness effects

Isothermal crystallization studies of low-density polyethylene (LDPE) and high-density polyethylene (HDPE) using differential scanning calorimetry (DSC) were performed using different sample thicknesses to determine the effect of non-ideal heat-transfer. Polyethylene was chosen because of its importance, its extensive coverage in the literature, and its fast crystallization kinetics. Thermal gradients were found to significantly affect the measured crystallization exotherm; slower crystallization rates were observed for thicker samples measured at lower temperatures (greater supercoolings). Differences between different sample thicknesses disappeared at higher temperatures, consistent with finite heat-transfer rates being responsible for the effect. A power-compensation and a heat-flux DSC were used; these experiments also enabled the determination that the performance of the latter was acceptable for this study. Finally, thickness-independent Avrami parameters have been calculated.     

A statistical degradation model for the service life prediction of aircraft coatings: With a comparison to an existing methodology

An advance on the model used by Guseva et al. [1] for estimating the service life of organic coatings under service conditions from accelerated test results has been developed. Instead of modelling just the times to failure, this new approach uses the complete degradation curve and allows for a more general specification of the failure time distribution. This modified model was then applied to the estimation of the service life (defined as gloss loss) for aircraft coatings and the results were compared to those obtained by Guseva et al. It was found that when this model was applied to the naturally weathered data, gloss loss (and thus failure times at a given level of gloss loss) followed a generalised gamma distribution, rather than the Weibull distribution identified by Guseva et al. Further, the new approach suggested a reduction in the warranty time of about one month. When the model was applied to the accelerated test data, it produced more accurate extrapolations of the median failure time associated with the naturally weathered data - (49.3 months compared to a measured 52 months obtained at the naturally weathered site). In fact, the extrapolated distribution obtained by this new approach was much closer to the distribution for the naturally weathered data than the extrapolated distribution obtained by Guseva et al.     

Multilinear gradient elution optimization in reversed-phase liquid chromatography based on logarithmic retention models: application to separation of a set of purines, pyrimidines and nucleosides

The analytical solutions of the fundamental equation of the multilinear gradient elution are derived in two cases, when the dependence of the logarithm of the solute retention (lnk) upon the volume fraction of organic modifier (φ) is a three-parameter logarithmic expression, and when a simple linear relationship between lnk and lnφ is adopted. The derived theoretical expressions for retention times under multilinear gradient conditions are embodied to simple algorithms for fitting gradient data and especially for resolution optimization. Their performance was examined by using a mixture of 16 model compounds chosen among purines, pyrimidine and nucleosides in eluting systems modified by acetonitrile. It was found that the accuracy of the predicted gradient retention times is very satisfactory even if the simple logarithmic expression for the retention behavior of solutes, i.e. the linear dependence of lnk upon lnφ, is used.