Extraction performance-structure relationship of polyamidoamine dendrimers on silica for online solid-phase...

Polyamidoamine dendrimers with different generations (G1-G5) were synthesized in situ on silica progressively via Michael addition and amidation reactions. A sequence of materials was characterized by elemental analysis and Brunauer-Emmett-Teller test, the content of each element (C, H and N) was increased but the surface area was reduced gradually from G1 to G5. These materials were separately packed in a stainless steel column (10 × 4.0 mm, i.d.) for SPE. These SPE columns were combined with high performance liquid chromatography (HPLC) to establish an online SPE-HPLC analysis. According to the chemical structures of materials, polycyclic aromatic hydrocarbons (PAHs) and bisphenols as model analytes were selected to investigate the extraction performance and the extraction mechanism, so as to reveal the extraction performance-structure relationship of G1-G5. The extraction performance was improved with the increase of functional groups from G1 to G4 or G5, the hydrophobic effect played main role accompanied with possible weak hydrophilic, hydrogen-bonding and electrostatic interactions in extraction mechanism. The adsorption capacity, enrichment factor, partition coefficient and extraction efficiency for PAHs and bisphenols reached to 17.52 µg g^-1 and 2.70 µg g^-1, 5353 and 3002, 5066 and 1197, and 90.09% and 60.05% respectively. Compared with commercial SPE materials, these dendrimer-grafted silica materials were inferior to C18, but better than silica. Furthermore, the G4 and G5 were separately selected to develop two online SPE-HPLC analytical methods for determining trace PAHs and bisphenols in real water samples, and satisfactory results were obtained.