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Electrochemical interaction between electrospray interface and separation column in the coupling of capillary electrophoresis with mass spectrometry
Alessandro Saba, A. P. Bruins
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Abstract
The current flowing through a separation column in CE generates reaction products at the inlet and outlet electrodes. OH- ions generated at the cathode can migrate into the CE column, change pH and thereby electro osmotic flow. These phenomena can be most clearly observed if the volume of inlet and outlet buffer reservoir is small. In the case of MS coupling, the CE/MS interface mimics the outlet buffer reservoir. When a coaxial make-up liquid is used, the outlet buffer reservoir has a small virtual volume, controlled by the make-up flow. Such volume is essentially zero for a sheathless interface. The effects of electrochemically generated ions has been studied and modifications to a coaxial CE/MS interface are investigated in order to eliminate interaction between interface and column.\nCE system: PRINCE Technologies programmable injector for CE. Mass spectrometer: NERMAG R 3010 triple quad with home made ESI source and CE/MS interface. The following parameters are monitored with a Sciex API 3 MS data system and a MacLab data acquisition system: mass spectra, UV absorbance, CE current, curtain plate current, orifice plate current, and skimmer current.\nThe effect of OH- ion migration into the column is reflected in the CE current. We have studied the effect of make-up liquid composition. It appears that a certain concentration of acid is needed to balance the OH- ions. The construction of the CE/MS interface has been modified. The stainless steel capillary which is normally present in a coaxial interface for ESI acts as the out let electrode for the CE column. This SS capillary was replaced by a fused silica capillary, and the outlet electrode was positioned in the make-up liquid line. The effect of position of this electrode is investigated, together with the effects of make-up flow rate and make-up solution composition. The correlation between experimental parameters and signals read by the data systems will be presented.