Separation and quantification of the linear and cyclic structures of polyamide-6 at the critical point of adsorption

The linear and cyclic structures of polyamide-6 were separated by liquid ch romatography at critical conditions (LCCC) and identified with different ma ss spectrometric (MS) techniques and quantitated by LCCC with evaporative l ight-scattering detection (ELSD). Electrospray ionization MS was not suitab le to identify the higher cyclic structures. For this purpose, matrix-assis ted laser desorption ionization time-of-flight MS performed better and cycl ic and linear structures were oligomerically resolved and separately identi fied in the mass spectrometer. The highest cyclic structure present and det ected was the cyclic pentacontamer. It could be demonstrated that cyclic an d linear oligomers follow different ionization and fragmentation routes/pat terns. Quantification with ELSD of the components separated by LCCC using a universal calibration curve or an iterative procedure was developed. An ar ea correction to account for different peak widths of coeluting components improves precision and accuracy of the calibration curve and improves quant itation accuracy for the samples analyzed. With these corrected values, no molecular mass dependency was observed for the cyclic and linear structures . Under critical conditions, the linear and cyclic structures of polyamide- 6 were separated, identified and quantified. (C) 2001 Published by Elsevier Science BN.