The field-amplified sample injection behavior of cationic tripropylamine(TPA) and anionic proline(Pro) at a positive voltage in capillary electrophoresis with tris(2,2′-bipyridyl)ruthenium(Ⅱ) electrochemiluminescence(ECL) detection system was studied. In the case of TPA, where the sample solution was prepared in pure water, ECL sensitivity can be improved by 100 times compared to conventional electroinjection method when a positive voltage was applied. Under the same positive voltage condition, anionic Pro prepared in electrolyte solution can also be injected and concentrated in the column when a water plug was injected before sample introduction. The sensitivity and efficiency were enhanced by 10 and 46 times, respectively. The behavior of cationic TPA can be explained by conventional field amplified sample injection(FASI)theory. When the ratio of resistivities of sample matrix to that of separation buffer is less than 1(γ1), the conventional FASI theory can also be used to explain the improved sensitivity and theoretical plates of Pro. The sensitivity, plate, velocity(v ep), amplified factor(v ep/v 0 ep) and peak variance(σ 2) of Pro reach maximum at optimized water plug length and buffer concentration of the sample matrix.
