A comparative study between a miniaturized liquid junction built in a capillary gap and semi-open capillaries for nL sample infusion to mass spectrometry

Abstract

This study introduces a novel design for the microfluidic element used in a high throughput screening (HTS) mass spectrometer autosampler. The original design of the sampler consists of a liquid bridge formed by a micrometer gap between two capillaries. This liquid bridge is used to receive the sample, which downstream is ionized and analyzed by mass spectrometry. The improvement described here consists in replacing the liquid bridge that is difficult to establish and maintain for long time periods by a single pierced capillary, called a “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 (EDM). The advantages of this design over the previous one is reduction of the dead volume and sample dilution, as well as higher stability. Characterization of the repeatability and limit of detection (LOD) show that the optimized semi-open capillary leads to nearly two-fold lower LOD when compared to the liquid bridge.