Evaluation of liquid chromatography column retentivity using macromolecular probes. III. Partition properties of C18 phases traced by polymers

Application of polymeric probes was proposed for evaluation of partition properties of the high performance liquid chromatographic stationary phases. The approach was tested with selected silica gel C-18 column packings. Polystyrene (PS) and poly(n-butyl methacrylate) (PnBMA) narrow molar mass standards of low polarity were applied to avoid adsorption of macromolecules on silanols and other polar groups present within column packings. Polar eluent components further reduced contingency of silanophilic interactions. The major eluent component was dimethylformamide (DMF), a thermodynamically poor solvent for polymer probes, which strongly promoted enthalpic partition of macromolecules in favor of the C18 bonded phase. Methyl ethyl ketone (MEK) and diethyl malonate (DEM) were also tested as the partition promoting eluent components. With polystyrenes, MEK was rather inefficient as a partition promoter while DEM was similarly active as DMF. A thermodynamically good solvent for polymer probes, viz. tetrahydrofuran (THF) was added to eluent to reduce and control the extent of partition. The differences in elution behavior of column tested indicate their unlike partition properties.