The use of sol–gel frits to minimize suction effects in capillary electrophoresis–nebulizer interfaces for plasma spectrometry†

A major experimental consideration, and often a difficulty when interfacing capillary electrophoresis (CE) with plasma mass spectrometry via a pneumatic nebulizer, is the suction effect caused by the natural aspiration of the nebulizer. This has a marked affect on the CE experiment, since it may lead to peak overlap and, ultimately, a completely degraded separation. Placing a sol–gel frit in the sample introduction end of the capillary in a CE system, interfaced with a pneumatic nebulizer at the outlet end of the capillary, minimizes the suction effect. A two-tube oscillating capillary nebulizer (OCN) was used in this study because of its very low liquid flow capacity and potential for interfacing to ICP-MS. To test the fritted capillary for possible application to CE-ICP-MS, standard ultraviolet (UV) absorbance detection was used for the CE separation of metallothionein and ferritin with a grounded nebulizer interface at one end of the capillary. With the capillary frit and OCN interface, reasonably true electropherograms were obtained when compared to the CE separation performed in the traditional mode without a frit and with a buffer reservoir in place at the outlet. Also, during this study it was found that a make-up buffer was necessary to maintain electrical contact to the outlet of the fritted electrophoretic capillary when using the OCN.