Methanol and dimethylformamide were evaluated for the separation of a series of inorganic anions. As these solvents were added to an aqueous electrolyte, the electroosmotic flow went through a minimum at 70-80% (v/ v) organic solvent and then increased as the composition approached that of the pure solvent Reproducibility of electroosmotic flow was good (%RSD = 1.1 for dimethylformamide), and Joule heating was not as important as in water systems. The effect of electrolyte concentration on electroosmotic flow was similar to that expected for aqueous solutions, but significant differences in separation selectivity were observed, with many ions showing reversed separation order compared to aqueous systems.

Six electrolytes were used to evaluate the performance (background noise) of amperometric detection with four electrode materials (C, Pt, Au, Ag). Both filament and disk electrodes ( -25-µ diameter) were placed either internal or external to the capillary. The large potential fields in the capillary were sufficient to cause oxidation and reduction of the electrolytes, often with bubble formation, along the length of the electrode placed inside the capillary, and electrodes could be dramatically altered when they were exposed to these potential fields. Measurement of the potential fields around the ends of capillaries with different internal diameters showed that the potential field had negligible effects on background noise for capillary internal diameters of <25 µ . Normal peak-to-peak noise observed with a simple potentiostat design was in the range of 0.05-0.1 pA for end-capillary detection (i.d. < 25 µ ). Potential fields were significant (~1 V) at the end of 75-µ capillaries, and the use of grounded detection zones gave only moderate improvements in peak-to-peak noise.The attractive potential of electrochemical detection in capillary electrophoresis (CE) has been shown for a wide range of analytes, including inorganic ions, small organic molecules, and large biomolecules.1-12 Attractive features of amperometric detection with ultramicroelectrodes include small detection volume, high sensitivity, good selectivity, and low cost. Most initial detector designs1 234 5™6 were based on the principle that to reduce detector noise from the potential field at the end of the capillary, the current in the capillary had to be connected to ground prior to the analyte reaching the working electrode. Indeed, the opinion has been expressed3 that some short-circuiting technique, such as cracking the capillary in front of the working electrode, is a requirement for effective electrochemical detection. These "grounded" detection cells can reduce the amount of the separation current passing through detection zone, but construction of such cells is difficult. It has also been noted4-6 that the background noise in these grounded systems is still affected by the (1) Curry,

The potential of nonaqueous capillary electrophoresis (CE) for the separation of hydrophobic solutes has been examined for a series of alkanesulfonates (C 2 -C 16 ), alkyl sulfates (C 8 -C 18 ), and linear alkyl benzenesulfonates. Sample loss and band broadening observed in aqueous CE separations was not observed in nonaqueous systems. Changes in separation selectivity induced by solvation and ion pair effects were examined. Separation selectivity was affected by changes in solvation and by a change from protic (methanol) to aprotic conditions (addition of acetonitrile). The addition of alkali metal ion caused changes in migration time via ion pairing but had only small effects on separation selectivity. However, the adjustment of the hydrophobicity of the electrolyte counterion was effective for separation optimization. The analytical features of these nonaqueous systems and applications to samples of shampoo, liquid detergent, and laundry detergents were also briefly examined. Alkanesulfonates and alkyl sulfates were separated in 0.01 mol/L sodium p-toluenesulfonate and 0.005 mol/L ptoluenesulfonic acid in methanol and in methanol/acetonitrile mixtures with indirect UV detection at 214 nm. Linear alkyl benzenesulfonates were separated in methanol and methanol/acetonitrile mixtures with tetramethylammonium as a counterion and direct detection at 214 nm.

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