An experimental consideration and common 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 is a significant effect in terms of the CE experiment, since it can seriously degrade the separation of analytes. In this study, a pneumatic microconcentric nebulizer was studied as a CE interface with inductively coupled plasma mass spectrometry (ICP-MS). A self-aspirating sheath flow interface technique was used to reduce the suction effect of the nebulizer by using a separation of metallothionein I and ferritin. However, the sheath flow or make-up buffer technique has not been studied sufficiently with respect to all the effects on the CE analysis. In this evaluation, a sol-gel frit was placed in the sample introduction end in this CE system, and the contribution of the suction effect to both sample response from sample loading and elution times was observed. It was found that the studied microconcentric nebulizer could be used effectively with the self-aspirating sheath flow technique; however, the contribution of the suction effect to sample loading to the CE system is very high. The peak area response difference of an open capillary vs. a sol-gel fritted capillary was approximately one order of magnitude greater. Also, the fritted capillary experiments showed that the contribution to migration time from aspiration of the nebulizer through the CE capillary is very significant.
Clayton B'Hymer, Jason A. Day, and Joseph A. Caruso, "Evaluation of a Microconcentric Nebulizer and Its Suction Effect in a Capillary Electrophoresis Interface with Inductively Coupled Plasma Mass Spectrometry," Appl. Spectrosc. 54, 1040-1046 (2000)