Monolithic and packed particle materials for in-line pre-concentration in capillary electrophoresis for 4-hydroxy-3-methoxy-methamphetamine and terbutaline

In-line solid-phase extraction (SPF) for capillary electrophoresis (CE) was investigated using a synthesized monolith and a commercial packing material. Terbutaline (TER) and 4-hydroxy-3-methoxy-methamphetamine (HMMA) with benzyl alcohol as the electro-osmotic flow marker were employed as model compounds. Two types of methacrylate-based monoliths, namely methacrylic acid-ethylene dimethacrylate and butylmethacrylate-ethylene dimethacrylate were examined. Preliminary results indicated that a nonaqueous separating medium is more suitable for these methacrylate monoliths than a purely aqueous medium (non-reproducible elution). However, coupling of the methacrylic acid-ethylene dimethacrylate with non-aqueous capillary electrophoresis could not provide good precision for the three model compounds. A packed-silica C18 SPE was also adopted by simply packing the C18 particles in situ in the separation capillary. Using an aqueous running buffer (10 mM phosphate buffer (PPB), pH 7), acceptable precision could be obtained with this type of SPE material. With a 10 min loading time and 20 min total analysis time, the pre-concentration factors were 333 and 1000 for TER and HMMA, respectively. The %RSD were less than 4.5 and 0.3 for the peak areas and migration times, respectively, for both HMMA and TER (n = 20).