Study of the aberrant retention behavior of a semi-crystalline polyamide in reversed-phase liquid chromatography
Year: 2025
Type: article
Abstract: The elution behavior of semi-crystalline polyamides (PAs) in reversed-phase liquid chromatography (RPLC) was examined. The aliphatic polyamide 4,6 (PA46) yielded a single broad chromatographic peak. However, the partly aromatic polyamide X (PAX) displayed a deviating elution profile, with both early- and late-eluting portions. RPLC experiments, encompassing varying injection and gradient conditions, showed changes in the relative abundance of the early and late-eluting portions of PAX. These bands were suspected to be due to the formation of amorphous and crystalline phases, respectively. Following RPLC analysis, the PAs were fractionated and the fractions were reinjected into the same RPLC system using unaltered conditions, and also subjected to size-exclusion chromatography. This revealed that the reinjected amorphous portion of PAX again showed two bands in RPLC. If the early- and late-eluting fractions are related to crystallinity, then (largely) amorphous and (largely) crystalline phases must be formed upon injection.To investigate our hypothesis for the underlying cause of the elution-profile variations, the crystallinity of the materials was examined. Differential scanning calorimetry (DSC) demonstrated that reducing the crystallinity of PAX decreased the relative abundance of the late-eluting fraction, approaching the behavior of aliphatic polyamides. Additional characterization by X-ray diffraction and static-light-scattering analyses confirmed the semi-crystallinity of the two solid PA samples. Although both small particles and larger aggregates were observed in solutions, these findings could not be attributed to the observed differences in elution profile of the PAs. Cloud-point measurements indicated that the solubility of both PA46 and PAX was largely independent of temperature. RPLC elution of the single broad PAX peak was observed only at low column temperatures, which occurred below the depressed melting point (analogous to the cloud point).The semi-crystallinity of PAX significantly influences its elution behavior in RPLC analysis. By optimizing the RPLC conditions to ensure the complete dissolution of the crystalline phase, it is possible to obtain chromatograms from which useful chemical information can be extracted.
Source: Journal of Chromatography A
Language: English
Subfield: Spectroscopy
Field: Chemistry
Domain: Physical Sciences
Open Access status: hybrid
Estimated APC paid: $4,040
OpenAlex ID: W4408906343