NAPHTHALENESULFONATES AS ELECTROLYTES FOR CAPILLARY ELECTROPHORESIS OF INORGANIC ANIONS, ORGANIC-ACIDS, AND SURFACTANTS WITH INDIRECT PHOTOMETRIC DETECTION

Naphthalene- mono-, di-, and trisulfonates (NMS, NDS, NTS) are introduced as electrolytes for capillary electrophoresis with indirect photometric detection (IPD) for a wide range of inorganic anions, organic acids, and aliphatic anionic surfactants. Several parameters such as the concentration of the UV-absorbing electrolyte, berate buffer, and organic modifier as well as temperature are found to influence sensitivity, resolution, and efficiency. However, the migration times of anions are affected only to a minor extent. A separation of 22 inorganic anions and organic acids in about 18 min using NDS is straightforward. A similar separation is possible using NTS in about the same time; however, the peak shapes of low mobility anions are slightly poorer. A close mobility match between an electrolyte and analyte can improve detection limits by at least 5-fold for certain inorganic anions such as fluoride and orthophosphate. Similar results are also obtained for organic acids such as formate and tartarate with NTS and NDS, respectively. Detection limits for the inorganic anions (16-300 mu g/L), and organic acids (40-100 mu g/L), are obtained at 284 and 288 nm with IPD using NTS or NDS. At 214 nm, these detection limits can be further improved by at least 2-fold. NMS having a significantly lower mobility is particularily well suited for the rapid separation in 6 min of C-4-C14SO4- or SO3- type surfactants. NDS was the best electrolyte for the separation of all three classes of anions.