Abstract: A sample pre-concentration method that combined field-amplified sample injection (FASI) induced by acetonitrile with transient isotachophoresis was applied to achieve effective concentration and the separation of cations in high-salt samples. Several important factors are discussed, such as buffer systems, terminating ions, column effective length and injection time of sample and terminating solution. A capillary column of 50 μm i.d.×65 cm (effective length of 50 cm) was employed. Solutions of 400 mmol/L LiAc-HAc (pH 4.5) and 400 mmol/L β-alanine-HAc (pH 4.5) were used as buffer solution and terminating electrolyte, respectively. The injection times of sample solution and terminating electrolyte were 270 and 90 s, respectively. Compared with conventional electrokinetic injection, the sensitivity of the proposed method was improved about 280-fold. The detection limits of propranolol and metoprolol achieved 2×10-3 and 8×10-3mg/L, respectively.

Key words: acetonitrile, capillary zone electrophoresis, field-amplified sample injection, high-salt sample , transient isotachophoresis