Determination of caprolactam and residual vinyl caprolactam monomer in soluplus by mixed mode gel permeation chromatography.

Soluplus, a graft copolymer of polyethylene glycol, vinyl caprolactam and vinyl acetate, is designed to solubilize poorly soluble active pharmaceutical ingredients. A straightforward aqueous gel permeation chromatography method that exploits both size exclusion and adsorption modes of separation was used to separate and quantify the related residual vinyl caprolactam monomer and caprolactam impurity present in Soluplus. This methodology offers a single step analysis of caprolactam and the residual vinyl caprolacatam monomer, yielding similar results to reversed-phase chromatography measurements, which are time-consuming and may involve multi-step sample preparation.