Evaluation of polarity indicators and stationary phases by principal component analysis in gas–liquid chromatography

Principal component analysis (PCA) was performed on a data matrix consisting of eight polarity indicators (scales) and 30 stationary phases. Calculations were carried out on the correlation matrices of values characterizing polarity/selectivity of liquid phases (columns). It was found that three principal components account for more than 99% of the total variance in the data, indicating that no single polarity variable is applicable on alone. The plots of component loadings and component scores showed significant groupings of polarity indicators and of stationary phases, respectively. The polarity indicators can be divided into two groups: (i) the sum of the first five McReynolds constants, Kovátsʹ coefficients, Castelloʹs ΔC values; (ii) Snyderʹs selectivity parameters. The latter differ from each other and from the other polarity indicators considerably. The physical meaning attributed to the most influential abstract factors, are as follows: Factor 1, polarity (according to McReynolds, Kováts and Castello); Factor 2, hydrogen donating and accepting ability; Factor 3, dipole interactions. Sequential analyses showed that polarity represents a nonlinear function among the phases.