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SummaryTwo modes of capillary electrophoresis (CE), capillary zone electrophoresis (CZE) and micellar electrokinetic chromatography (MEKC), were investigated for the separation of 12 aromatic sulphonate compounds. In CZE, although the voltage applied, the buffer concentration and the pH were optimized for effective separation of the compounds studied, under the best conditions four of the five amino compounds coeluted, as did naphthalene-l-sulphonic acid and naphthalene-2-sulphonic acid. In MEKC, sodium dodecyl sulphate (SDS) and Brij 35 were chosen as the anionic and nonionic surfactants and the effect of the concentration of micelles was examined. The effect of adding methanol as the organic modifier was also investigated with each of these micellar systems. All the analytes, including the isomers, were completely separated by use of MEKC with Brij 35 but when SDS was used only 11 compounds were separated because two amino compounds coeluted.

We investigated the on-line preconcentration of a test mixture of 15 substituted and unsubstituted naphthalene(NSs) and benzenesulfonates (BZSs) by large-volume sample stacking (LVSS). Analyses were carried out by capillary zone electrophoresis (CZE) with on-column UV detection. In particular, we focused on how experimental variables such as the inside diameter of the capillary, the volume of sample introduced and polarity switching influenced the enrichment procedure. The best results were obtained when 300 nl were injected and stacked using a bubble cell capillary. Under these conditions, LVSS increased the detector response of conventional hydrodynamic injection by a factor of 40. The limits of detection of the method were between 5 and 10 microg l(-1). Determinations were reproducible, in terms of peak area and migration time, under such conditions. The performance of the method was examined by determining NS and BZS in real samples, such as tap, river and surface waters and inflow/outflow waters from a water treatment plant. Real samples were injected directly into the CZE column with little or no preparation.

We investigated the separation of a test mixture of nine substituted and unsubstituted naphthalenedisulfonate isomers by capillary electrophoresis with a UV diode array detector. In particular, we focused on how the composition of the running buffer affected the separation selectivity. When capillary zone electrophoresis was carried out, the best results were obtained when organic solvents such as ethanol or propan-2-ol were added. Eight peaks were baseline separated but in no case were all the unsubstituted isomers separated. Therefore, capillary electrophoretic separation of the compounds was examined in the presence of micellar agents, such as sodium dodecyl sulfate, polyethylene glycol dodecyl ether (Brij 35) and cetyltrimethylammonium bromide. All the substituted isomers and two of the unsubstituted isomers were well resolved within 20 min by micellar electrokinetic capillary chromatography when Brij 35 was used as micellar agent. Separations were reproducible, in terms of peak area and migration time, under these conditions.

SummaryCoelectroosmotic micellar electrokinetic chromatography (coelectroosmotic MEKC) has been investigated for the separation of twelve aromatic sulfonate compounds. The advantage of this method is that it combines the efficient separation characteristic of MEKC and the short analysis time of the coelectroosmotic mode. MEKC was performed with either cetyltrimethylammonium bromide (CTAB) or polyethylene glycol dodecyl ether (Brij 35) surfactants as pseudostationary phases and 2-propanol as organic modifier. The electroosm0tic flow (EOF) was reversed by adding two types of EOF modifier, an alkylammonitro salt (cetyltrimethylammonium bromide, CTAB) or a cationic polyelectrolyte (hexadimetrine bromide, HDB). The surfactant concentration, applied voltage, and temperature were optimized, the influence of 2-propanol on the MEKC resolution of the compounds was studied. The effect of the osmotic modifier on the separation was also investigated.

SummaryCoelectroosmotic capillary zone electrophoresis (CZE) has been investigated as a means of rapid analysis of twelve aromatic sulphonate compounds. The main factors affecting reversal of electroosmotic flow (EOF) -type of osmotic modifier and concentration -were studied. Two types of osmotic modifier, an alkylammoniun salt (cetyltrimethylammonium bromide, CTAB) and a cationic polyelectrolyte (hexadimetrine bromide, HDB) were investigated. The composition of the running buffers was optimized according to the characteristics of each osmotic modifier. A concentration of HDB as low as 0.0001% (w/v) was used successfully to provide a stable and reversed EOF.

We explored isotachophoresis-capillary zone electrophoresis (ITP-CZE) with diode array detection on a single capillary to find out how to increase the injection volume and decrease the detection limits of aromatic sulfonates in CZE. The ITP was performed by applying a negative voltage in conjunction with hydrodynamic backpressure programming, and the terminating buffer was removed before the CZE separation, which resulted in highly sensitive determinations. The ITP increased the signal response of conventional hydrodynamic injection by a factor of 100, whereas the separation efficiency was unaffected. The limits of detection of the method were between 3 and 5 nugL(-1). The method was successfully used to determine these compounds in water samples. Experimental conditions for capillary electrophoresis-mass spectrometry were optimized and applied to determine aromatic sulfonates in water samples. These techniques enables the 2-naphthalenesulfonate to be determined in water samples.

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