Development and characterization of a capillary gap sampler as new microfluidic device for fast and direct analysis of low sample amounts by ESI-MS.

Direct hyphenation of miniaturized sampling devices to electrospray ionization-mass spectrometry (ESI-MS) is attractive because ESI-MS is compatible with microfluidics and allows comprehensive sample analysis, yielding information that is orthogonal to that available from optical methods. We present a "capillary gap sampler" as a platform for directly connecting microfluidics to μ-ESI-MS. The sampler was designed to be robust, light and compact, and to allow precise and fast liquid handling. Sample introduction in the range of a few nanoliters is performed via an open liquid bridge as a new microfluidic element. This allows minimum contact of the sample with system surfaces during the infusion process. The system shows good performance characteristics such as symmetrical peak shapes, low sample carryover (below 1%), and total injection cycle times of less than 15 s. This new device thus has the potential for rapid analysis of biomedical and pharmaceutical samples with limited sample amounts in a high-throughput mode.