Capillary electrochromatography with 1.5 μm ODS-modified non-porous silica spheres

Abstract

SummaryThe particle realization of electrochromatography on capillaries packed with 1.5 /am ODS-modified nonporous silica spheres is demonstrated. In order to realize stable separation conditions it is crucial to add sodium dodecylsulphate (SDS) to the mobile phase and to pressurize both buffer vials at 10 bar. The presence of SDS stabilizes the current and makes the electro-osmotic flow in the packing more uniform so that no air bubbles are generated at high field strengths. The capillary columns are extremely efficient and on a 24 cm long column about 120,000 plates can be generated (a reduced plate height of about 1.3). The columns are very stable and no loss in efficiency was found after using a column continuously for two months.bolic. Further the electroosmotic flow depends only on the nature of the surface of the particles and is thus independent of the size of the channels. This means that in electrochromatography in principle reasonable flow rates can be generated on capillary columns length packed with sub-micron particles.In the last years the practical problems encountered with capillary electrochromatography (CEC), e.g., bubble formation and difficulties with the preparation of the terminal frits, have been solved satisfactorily [6][7][8][9][10] and the applicability of the technique with 3-5/am particles has been demonstrated now frequently [7,16]. So far only a few number of papers have been appeared dealing with smaller particles. Knox and Grant [6] and Yamamoto et.al [17] demonstrated CEC with nonporous silica particles of 1.6/am and Smith and Evans [7] used 1.8/am porous Zorbax particles. In this paper we report the results of an investigation to apply electrochromatography on capillaries packed with 1.5/am ODS modified non-porous silica particles. Attention will be given to the preparation of the column, the effect of the addition of SDS on the performance and the effect of the composition of the mobile phase on the efficiency. Illustrative chromatograms will be shown.

Separation of related opiate compounds using capillary electrochromatography

“…Another approach is to add a surfactant such as SDS to the mobile phase. This method is easy and very effective for reducing bubble formation in CEC separations, as described previously by several research groups [38,39]. For the prevention of bubble formation in the CEC separation of opiates, therefore, we added 5 mM SDS, whose concentration is lower than the CMC of 8.1 mM [40].…”

Evaluation of 1.5 μm reversed phase nonporous silica in packed capillary electrochromatography and application in pharmaceutical analysis

“…The porous material showed 12±15 times higher k values and 50 times greater loading capacity compared to the nonporous silica, although efficiency was lower. During their study concerning RP-NPS, Seifar and co-workers [32] encountered problems with the packed bed drying out as higher voltages were applied. In order to prevent this and stabilize the EOF, they added 1±5 mM of SDS.…”

Continuous bed columns containing sol-gel bonded large-pore octadecylsilica for capillary electrochromatography

“…the electroosmotic flow EOF and the use of long w x columns, respectively. Seifar et al 7 performed CEC separations and obtained an efficiency of 500,000 plates per meter with a 32r24 cm = 50 m i.d. column packed with 1.5 m nonporous ODS.…”