Sol–gel immobilized short-chain poly(ethylene glycol) coating for capillary microextraction of underivatized polar analytes

Sol–gel coating with covalently bonded low-molecular-weight (MW < 300 Da) poly(ethylene glycol) (PEG) chains was developed for capillary microextraction (CME). The sol–gel chemistry proved effective in the immobilization of low-molecular-weight PEGs thanks to the formation of chemical bonds between the organic–inorganic hybrid sol–gel PEG coating and the fused silica capillary inner surface. This chemical anchorage provided excellent thermal and solvent stability to the created sol–gel PEG coating as is evidenced by its high upper limit of allowable conditioning temperature (340 °C) and its practically identical performance before and after rinsing with various solvents. The prepared sol–gel PEG coating provided simultaneous extraction of moderately polar and highly polar analytes from aqueous samples without requiring derivatization, pH adjustment or salting-out procedures. Detection limits on the order of nanogram per liter (ng/L) were achieved in CME–GC–flame ionization detection experiments designed for the preconcentration and trace analysis of both highly polar and moderately polar compounds extracted directly from aqueous media using sol–gel short-chain PEG coated microextraction capillaries.