PNNL

Abstract

We report the first observations of aqueous surfaces by a time-of-flight secondary ion mass spectrometer (ToF-SIMS) via a self-contained microfluidic module compatible in vacuum. The interface uses a microfluidic channel with a 3 µm diameter window into the flowing fluid beneath it. This window supports the liquid against the vacuum by the liquid’s surface tension and limits the high-density vapor region traversed by the probe beams to only a few micrometers. We demonstrate detections of aqueous surfaces such as deuterium water and sodium iodide (NaI) solution through the small aperture by ToF-SIMS. Even more, molecular signals (M-H-) of glutamic acid (C5H8NO4-) are observed. ToF-SIMS coupled with the novel interface provides a molecular recognition capability, making it a great choice to detect short-lifetime reaction intermediates in aqueous solutions. This novel microfluidic interface makes multimodal vacuum based analysis of liquid surface possible.