Microfluidic self-aspiration sonic-spray ionization chip with single and dual ionization channels for mass spectrometry

Abstract

The coupling of microfluidic chip-based ionization to mass spectrometry (MS) has recently gained considerable attention in the mass spectrometry community. In consideration of the miniaturization, integration, and universal disadvantages of microfluidic chip-based ionization coupled with MS, this study proposed a novel microfluidic self-aspiration sonic-spray ionization chip. The proposed ionization chip was fabricated using three-layer soft lithography technology without the need to fabricate the spraying tips. Simulations were performed to validate and optimize the microfluidic structure for self-aspiration. Corresponding experimental results were obtained by characterizing and comparing the MS signals of different microfluidic chip structures coupled with an ion-trap MS. MS signals of different gases for sonic-spray ionization of different liquid samples were also compared. The results indicated that the proposed microfluidic chip can implement the ionization of liquid samples, depending simply on the gas applied on the sheath flow channel, with a much lower gas pressure. Moreover, a dual-channel self-aspiration sonic-spray ionization chip was implemented, which might realize internal calibration for MS. We preliminarily proved the intensity enhancement by applying the same sample in both channels and reduced the ion suppression by applying different samples in different channels. This microfluidic chip significantly improved the integration of ionization and simplified the operation of such a device, making it particularly suitable for coupling with portable MS in the future.