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Experimental design methodology was used to optimize the linear gradient elution chromatography. The effect of initial mobile phase composition (phi(in)), initial isocratic time (t(in)), and gradient time (t(G)) on the retention times of phenyl thiohydantoin aminoacids (PTH-amino acids) was investigated. The experiments were performed according to Box-Behnken experimental design to map the chromatographic response surface. Then multiple linear regression and support vector machine (SVM) methods were used to fit the retention times of solutes. Results shows the SVM models have better ability to predict retention time and used for grid search in factor space. The SVM models were verified, as good agreement was observed between the predicted and experimental values of retention time in the optimal condition.

Half-wave potentials (E1/2) are an important electrochemical property of organic compounds, which depends on both solute and solvent. In this work, a quantitative structure–property relationship (QSPR) study was carried out to predict the reduction E1/2 behavior of 15 substituted nitrobenzenes in five solvents, including acetonitrile, N,N-dimethylformamide, dimethyl sulfoxide, methanol, and tetrahydrofuran. For selection of the most relevant descriptors, a stepwise multiple linear regression (MLR) technique was used. Five descriptors that appeared in the MLR model were: minimum charges of the oxygen atom in the nitro group, Guttmann acceptor number of the solvent, dipole moment of solute, dipole moment of the solvent, and Hammet substitution constant (σ). The leave-one out cross validation method was used to evaluate the credibility of the model. Statistical parameters derived from this test are: R2 = 0.960, Q2 = 0.959, and SPREES = 0.046. These indicate the suitability of the constructed model.

Short CommunicationOptimization of the separation of chlorophenols with stepwise gradient elution in reversed phase liquid chromatography An optimization technique based on gradient elution was used to separate eleven chlorophenols by reversed phase liquid chromatography. The separation was based on gradient elution with a stepwise variation pattern of the volume fraction of organic modifier, u, in the mobile phase. Initially, two-, three-, and four-parameter equations which describe the dependence of ln k9 upon u, were examined for their ability to fit the experimental data. It was found that, among these equations, the four-parameter equation gave the best fit of the experimental data. In addition to separation optimization, a non-linear least squares program with a grid search for initial estimates was used to determine the best variation pattern. The best variation pattern was obtained with u 1 = 0.27, u 2 = 0.39, u 3 = 0.62, t 1 = 33 min, and t 2 = 11 min. This pattern allowed the chromatographic separation of the chlorophenols with a good resolution and a total analysis time of 51 min. Good agreement was observed between predicted and experimental values of the retention times under optimal condition.

The chemometrics approach was applied to the optimization of separation of quinolines in micellar liquid chromatography (MLC). The effect of four experimental parameters on chromatographic retention time was investigated by means of multivariate analysis. The factors considered were the concentration of sodium dodecyl sulfate (SDS), the organic modifier concentration and the length of its alkyl chain, and pH of the mobile phase. The experiments were performed according to a face centered cube response surface experimental design. In order to optimize the separation a Pareto-optimality method was employed. The models were verified, because a good agreement was observed between the predicted and experimental values of the chromatographic response function in the optimal condition. The obtained regression models were characterized by both descriptive and predictive ability (R 2 ≥0.97 and 2 cv R ≥0.92) and allowed the chromatographic separation of the quinolines with a good resolution and a total analysis time of 50 min.