Development and Application of a Dual Detection Concept (Amperometry-Mass Spectrometry) for Capillary Electrophoresis

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The high complexity of samples in medical and environmental applications and the increasing number of analyses in shorter time-scales demand new developments of powerful instrumental analytical systems. Separation techniques coupled to dual detection methods are capable of generating a large amount of information in one run because of the separation of analytes and the combined data from both detection methods.In this project, a dual detection concept for hyphenation of capillary electrophoresis (CE) - a separation method based on the migration of charged species in an electrical field, which allows for short separation times and low consumption of samples and solvents - with amperometric detection (AD) and mass spectrometry (MS) is planned. AD is well suited for quantification in capillary electrophoresis due to its unmatched sensitivity at low amounts of sample as they occur in capillary electrophoresis. However, it is not possible to identify substances or to spot comigrations. In contrast, MS can identify unknown substances based on their mass spectra and corresponding molecular formulas. However, the limits of detection (depending on the analytes) obtained with CE-MS are typically in the range of 10-6 M which is about two magnitudes of order higher than currently obtained in CE-AD. With the newest generation of potentiostats the limits of AD can even be lowered. In addition, due to the complexity of electrospray ionization quantification has usually to be based on the use of isotope labelled standards, which can be expensive and are not always available. Thus, the CE-AD/MS concept provides complementary data and information.As both detectors cannot be placed one after the other due to their destructive properties, a new concept has to be developed to split the high voltage-driven flow through the separation capillary onto both detectors. The instrumental development of an optimized coupling device for CE-AD/MS should enable a precise control of both microfluidic flow streams. Ferrocene derivatives can serve as internal standards to calculate effective mobilities of the analytes. In this way an unambiguous assignment of AD and MS signals can be achieved even if migration times tend to shift.The amount of analyte in the sample can be quantified by AD, which is very sensitive and easy to handle, while substance identification and peak purity can be validated by MS to avoid false results. Additionally, due to the complementary detection principles, substances that cannot be detected with one detector can often be detected with the other so that a broader range of components in complex samples can be analyzed.Thus, the novel CE-AD/MS concept provides a high information density and universality so that it can contribute to the analysis of complex samples.