Stable cross-linked polyacrylamide stationary phase based on atom transfer radical polymerization for hydrophilic interaction liquid chromatography

Crosslinked and uncrosslinked polyacrylamide stationary phases were prepared on porous silica gel (SiL-PAAm) by atom transfer radical polymerization (ATRP), and their hydrophilic interaction liquid chromatography (HILIC) separation performance and stability were evaluated systematically. After aminosilylation and esterification with 2-bromoisobutyryl bromide on silica gel, surface-initiated ATRP with acrylamide or acrylamide/N,N’-methylenebisacrylamide mixtures at molar ratios of 1:0.1 and 1:0.2 was carried out, and SiL-PAAm-0, SiL-PAAm-10, and SiL-PAAm-20 HILIC materials were obtained. SiL-PAAms were characterized by FT-IR, TGA and nitrogen adsorption–desorption isotherms. It was confirmed that these three SiL-PAAms had very similar specific surface area of 130–143 m 2 g −1 , pore size of 8.67–8.89 nm, and PAAm bonding amount of 177–181 mg g −1 . Their HILIC performances were evaluated and compared by separating nucleosides, vitamins, sugars, and amino acids, respectively. It was found that SiL-PAAms exhibited significantly stronger retention and higher separation selectivity than both bare silica and commercial amide columns. However, an excessive increase in the crosslinking degree also led to a decrease in retention strength. Additionally, the SiL-PAAm-10 and SiL-PAAm-20 exhibited significantly reduced column bleeding and enhanced reproducibility, far surpassing both SiL-PAAm-0 and commercial amide columns. Generally, the suitably crosslinked PAAm by ATRP has been proven as one highly efficient and robust HILIC stationary phase for the chromatographic separation of a wide range of polar compounds.