Poly(butylene terephthalate) based novel stationary phase (SP), composed of planar aromatic phenyl group together with ester group monomer units, was designed for supercritical fluid chromatography (SFC) use. As expected from its structure, this phase shows planarity recognition of isomeric aromatics and closely similar compounds. Interestingly, for most analytes, the retention behavior of this SP is significantly distinct from that of the 2-ethylpyridine based SPs which is among the most well-known SFC dedicated phases. Although the poly(butylene terephthalate) is coated on silica gel, the performance of the column did not change by using extended range modifiers such as THF, dichloromethane or ethyl acetate and column robustness was confirmed by cycle durability testing.

A novel poly(4-vinylpyridine) based stationary phase was investigated for its performance under supercritical fluid chromatography (SFC) mode. Due to its unique structure, this stationary phase has high molecular planarity recognition ability for aromatic samples possessing the same number of aromatic rings and π-electrons. Taking advantage of the planarity recognition ability observed, separations of structurally similar polycyclic aromatic hydrocarbons and steroids were achieved. This novel stationary phase afforded good peak symmetry for both acidic and basic active pharmaceutical ingredients even when excluding the use of additives such as acids, bases, and salts. These findings may be attributed to the polymeric pyridyl groups covalently-attached on silica gel, which will effectively shield the undesirable interaction between residual silanol groups on the surface and the analytes. Moreover, the properties of pyridyl group on the selector can be reversibly tuned to cationic pyridinium form by eluting trifluoroacetic acid containing modifier. Column robustness toward cycle durability testing was also confirmed.

To understand the selectivity of the crown ether type chiral stationary phase (CSP), the retention selectivity for aniline and the positional isomers of substituted anilines were studied. In various substituted isomers, except nitroaniline, a remarkable decrease of retention due to steric hindrance was observed for the 2-substituted isomer. To determine the detailed molecular recognition mechanism, quantum chemical calculations were performed for the aggregates between the crown ether and the anilines. The results suggested that the 20-Crown-6, which includes a phenyl-substituted 1,1′-binaphthyl moiety, interacts with alkyl and aryl amines in an unconventional form different from the proposed one for 18-Crown-6.

Owing to their high selectivity and low toxicity, synthetic cyclic peptides hold promise as bioactive therapeutics. The corresponding impurity analysis typically relies on reversed-phase high-performance liquid chromatography (RP-HPLC), which, however, often provides inaccurate results because of the abundance of chemically similar impurities. To bridge this gap, hydrophilic-interaction liquid chromatography (HILIC), a technique orthogonal to RP-HPLC, was herein used with an ultraviolet detector to analyze the impurities of four cyclic peptides. Each of these peptides comprises nine amino acids (both natural and nonnatural) and features neutral, acidic, basic, or zwitterionic residues incorporated at positions 3 and 6. Three polymer-based HILIC columns (acidic, basic and zwitterionic) were newly employed, and seven mobile phases were used to investigate the effects of additives and pH. Derringer's desirability functions based on five criteria (purity, impurity factor, peak symmetry factor, theoretical plate number, and retention time) were employed to identify optimal screening conditions. Ammonium acetate was identified as an effective additive, and polymeric selectors with vinylpyridine and phosphoryl choline residues were shown to be effective irrespective of the peptide features. Optimized HILIC conditions were established for each peptide, and the corresponding impurity elution profiles were compared with those obtained by RP-HPLC using a column filled with octadecylsilyl-functionalized silica. RP-HPLC and HILIC were revealed to be mutually orthogonal, i.e., most impurities with small RP-HPLC retention times had large HILIC retention times, and vice versa. The results help make the purity evaluation of synthetic peptides more accurate, thus paving the way for their efficient purification.