A comparative study between a miniaturized liquid junction built in a capillary gap and semi-open capillaries for nL sample infusion to mass spectrometry
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This study introduces a novel design for a microfluidic element used in a high-throughput screening mass spectrometer autosampler. The original design of the sampler consists of a liquid bridge formed in a micrometer gap between two capillaries. This liquid bridge is used to receive the sample, which is later ionized and analyzed by mass spectrometry. However, this liquid bridge is difficult to establish and maintain for long time periods, making the screening of large libraries of compounds a tedious task. The improvement described here consists in replacing the liquid bridge by a single pierced capillary, called “semi-open capillary”. The fabrication of semi-open capillaries is explained. To achieve an optimum structure, two different machining methods were tested, laser ablation and electro-discharge micromachining. The advantages of this design over the previous one include reduction of the dead volume and that of the sample dilution, as well as higher stability. Characterizations of the repeatability and the limit of detection (LOD) show that the optimized semi-open capillary leads to nearly twofold lower LOD when compared to the original liquid bridge.
KeywordsHigh-throughput screening Capillary gap sampler Semi-open capillary Laser ablation Electro-discharging machining Sensitivity
We gratefully thank Dr. Christof Fattinger (Roche) for his support in sampler development and Professor Ying Zhu (Department Chemistry, Zhejiang University) for helping in optimizing the structure of the hole. Moreover, we thank the Scientific Center for Optical and Electron Microscopy (ScopeM), a central technology platform of ETH Zurich, for providing us with resources and services in electron microscopy, the ETH Physics workshop for performing EDM for semi-open capillary preparation, and the SuSoS company in Dübendorf for providing us with a PFAND solution and for recording XPS data. Finally, we thank the Swiss National Science Foundation (SNSF) for funding this project (Grant Nos. 200020-159929 & 200020-178765).
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