On-line pre-concentration techniques in capillary electrophoresis for environmental analysis

Abstract

This work focused on the development of on-line sample pre-concentration techniques to improve detection sensitivity in capillary electrophoresis (CE) for environmental analysis. Several on-line enrichment methods were established for acidic compounds with various pKa values, including a strong acid (nitrate), weak acids (haloacetic acids, phenoxy acids, pKa 0.6-4.8) and very weak acids (phenols, pKa 7.5-10.6) in different sample matrices.In CE, the sample matrix plays an important role in developing on-line pre-concentration techniques. For enrichment of nitrate in seawater sample, a leading-type transient isotachophoresis was employed, in which natural chloride in the sample functioned as a leading ion. The co-ions in the background electrolyte (BGE) functioned as a terminating ion. Weakly acidic compounds (haloacetic acids, phenoxy acids and phenols) were usually dissolved in NaOH solution during off-line sample pretreatment. These compounds in NaOH solution were pre-concentrated with either a low-pH BGE or BGEs with weak bases as counter-ions.