Probing Aqueous Surfaces by TOF-SIMS - - Spectroscopy
 Home   Mass Spectrometry   ICP-MS   Infrared   FT-IR   UV-Vis   Raman   NMR   X-Ray   Fluorescence  
Issue Archive
Special Issues
The Application Notebook
Current Issue
Submission Guidelines
Digital Edition
Subscribe to the Digital Edition
The Wavelength
Subcribe to The Wavelength
Subscribe to the MS E-news
Market Profiles
Information for Authors
Lab TV
Advertiser services
Contact Us
Atomic Perspectives
Chemometrics in Spectroscopy
Focus on Quality
Laser and Optics Interface
Mass Spectrometry Forum
The Baseline
Molecular Spectroscopy Workbench

Probing Aqueous Surfaces by TOF-SIMS

Special Issues

We report the first observations of aqueous surfaces by time-of-flight secondary ion mass spectrometry (TOF-SIMS) via a self-contained microfluidic module compatible with a vacuum. The interface uses a microfluidic channel with a 3-Ám 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 detection of aqueous surfaces such as deuterium water and sodium iodide (NaI) solution through the small aperture by TOF-SIMS. A molecular signal (C5H8NO4 = [M-H]-) of glutamic acid also was observed. TOF-SIMS coupled with the 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 surfaces possible.

This article describes a breakthrough using a microfluidic interface to conduct sensitive time-of-flight secondary ion mass spectrometry (TOF-SIMS) analysis and study liquid surfaces in situ under vacuum conditions. Applications in TOF-SIMS so far have been limited to solid surfaces or low-vapor-pressure liquid surfaces.

TOF-SIMS has been applied in applications such as polymers (1), pharmaceuticals (2), semiconductors (3), environmental chemistry (4), inorganic surfaces (5), corrosion and monitoring of organic coating processes, catalysis (6), investigation of surface contamination (7), geology (8), and archaeology (9). However, a lot of chemistry takes place at the interface of liquid phases with gases in environmental, industrial, and biological systems. The surfaces of these aqueous phases and films (when <1-nm thick) have unique kinetics and thermodynamics that are distinct from those of the bulk materials (10–12). Although TOF-SIMS has already been used to investigate ionic liquids (13), lubricants (14,15), and liquid crystals (16,17), which all have very low vapor pressure, no one has been able to analyze high-vapor-pressure aqueous solutions (to the best of our knowledge). Because TOF-SIMS is vacuum-based, one cannot easily probe these high-vapor-pressure interfaces. Our goal is to permit studies of high-vapor-pressure liquid surfaces in TOF-SIMS.

Figure 1: A schematic of the TOF-SIMS instrument.
TOF-SIMS offers great sensitivity and attractive spatial resolution as an advanced vacuum-based surface analytical technique. It uses a focused ion beam to raster over the surface, ejecting molecules, atoms, and molecular fragments (neutral and ionic) from the top layer, and a TOF mass spectrum is obtained for each pixel (see Figure 1). TOF-SIMS gives high mass resolution (mm > 10,000) and high lateral resolution (<100 nm), a great advantage in exploring complex samples. Automated charge compensation permits the study of insulators. Simultaneous auxiliary ion sputtering permits depth profiling and 3D chemical maps. Negative or positive emitted ions can be monitored. Sensitivity is typically in a range of 0.1–10 ppm.

In this article, we will describe the first aqueous surface detections by TOF-SIMS enabled by a microfluidic interface designed for operation in vacuum conditions. We demonstrate new TOF-SIMS applications using different liquid samples prepared in the laboratory. Directions for using this unique technique in future developments are also presented.

Rate This Article
Your original vote has been tallied and is included in the ratings results.
View our top pages
Average rating for this page is: 10
Headlines from LCGC North America and Chromatography Online
Agilent NA - Screen Beer by GC/MS Static Headspace with the Agilent J&amp;W DB-624 Ultra Inert Capillary Column
Waters NA - Multi-Residue Pesticide Analysis in Ginseng Powder
Agilent EU - Screen Beer by GC&ndash;MS Static Headspace with the Agilent J&amp;W DB-624 Ultra Inert Capillary Column
Agilent NA - Analysis of Pesticide Residues in Chicken Muscle with QuEChERS and Triple Quadrupole GC
Agilent NA - Optimizing Sample Preparation for LC/MS/MS of Pesticide Residues in Herbal Teas
Source: Special Issues,
Click here