A chip-based supersonic microfluidic nebulizer for efficient sample introduction into inductively coupled plasma - Mass spectrometry

Abstract

As the use of microfluidic chips for handling biological samples is increasing, so is the need for combining them with powerful analytical techniques for metal determination such as inductively-coupled plasma mass spectrometry (ICP-MS). So far, coupling a microfluidic chip to an ICP-MS has been demonstrated mainly through the use of conventional pneumatic micro-flow nebulizers. However, disadvantages associated with the use of such nebulizers entail dead volume issues and liquid suction exerted on the outlet channel of the chip. Herein, we propose that a microfluidic chip, bearing a pneumatic nozzle for liquid nebulization, has the potential to advance metal determination in chip-based ICP-MS. More specifically, we demonstrate for the first time that the coupling of a chip-based supersonic microfluidic nebulizer (chip-μf-Neb) to an ICP-MS can be conveniently achieved through the use of a spray chamber with a laminar flow makeup gas. Operation of the combined system was evaluated at low liquid flow rates across 0.5-20 μL min^-1, while nebulization and makeup argon (Ar) gas flow rates were optimized with respect to maximizing indium (In) sensitivity and minimizing oxide formation; a maximum sensitivity of 40000 cps (μg L^-1)^-1 was achieved at 10 μL min^-1. The system was further evaluated for its performance in single-particle analysis, featuring a transport efficiency of 46% for Ag nanoparticles. Finally, the capabilities for conducting single-cell analysis were demonstrated with the detection of ⁸⁰Se and ⁷⁵As in individual Chlamydomas reinhardtii cells, which were previously incubated in 20 μM of selenate and 300 μM of arsenate, respectively. Efficient operation at low liquid flow rates along with the absence of self-aspiration render this nebulizer a promising tool for combining the powerful field of microfluidics with metal quantitation by means of ICP-MS.

Keywords: Chip-based nebulizer; Inductively coupled plasma; Mass spectrometry; Microfluidics.