Analysis of biomolecules on surfaces is essential to various applications of biosensors and biomolecule engineering. Matrix-assisted laser desorption/ionisation (MALDI) is now an established technique for mass spectrometry of biomolecules. Different matrix-analyte preparation protocols have been shown to influence the desorption or ablation process resulting in either high or low metastable fragmentation. It has been speculated that following laser ablation the velocities of the analyte and matrix can be regarded as a valuable and meaningful characteristic of the MALDI process. However, the interaction and distribution of the analyte with respect to the matrix is poorly understood. Here we study the distribution of a selection of biomolecules as a function of matrix material using high resolution imaging X-ray photoelectron spectroscopy (XPS).
An AXIS spectrometer was used to probe the surface chemistry of a widely used ionic liquid. The elemental surface composition was analysed and information was gained regarding the various chemical environments of the surface elements. Traditional surface analysis techniques such as ARXPS were exploited to determine the orientation of the mobile molecules in the uppermost layer of the liquid. The stability of the liquids under X-ray irradiation was also investigated.
XPS imaging is an important tool for investigating the lateral distribution of surface chemistry on the micron scale. Photoelectrons emitted from core electronic levels of surface atoms may be focused to form a two dimensional image on a suitable detector to allow the lateral distribution of the photoelectrons to be determined. AXIS spectrometers have a pulse counting delay line detector (DLD) system which allows images to be quantified. Spectra may be generated from every pixel in an image hence the chemical state of a sample surface may be quantitatively determined at high lateral and high energy resolution. In this example silicon dioxide particles dispersed on the surface of a silicon wafer were analysed to demonstrate the flexibility of XPS imaging.
Evaluation of Anti-Adhesive Coatings on Medical Textiles by XPS
XPS is a well-established method for the chemical characterisation of material surfaces. Key developments in recent years, including imaging, have resulted in a wider range of applications. Manufacturers and suppliers of both commercial and technical textiles are now exploiting XPS as an ideal tool to aid the development and optimisation of the types of surface coating/treatment demanded by industry and consumers.
Here we investigate the oxidation of Co(OH)2 using the catalysis cell. The catalysis cell allowed us to treat the sample under high temperature high pressure conditions similar to those found in industrial reactors. Careful analysis of the XPS spectra generated after each successive treatment shows that once calcined above 200 ºC the surface of the catalyst changes from hydroxide to oxide. Peak fitting the Co 2p region identified Co to be present as Co3O4.
Overlapping photoelectron lines and Auger features are a common problem in analysis of complex materials. The standard approach of switching to an achromatic Mg X-ray source is sometimes undesirable due to the introduction of X-ray satellites into the spectrum. In this example we show how Kratos’ automatic monochromatic Ag Lα X-ray source may be used to excite a satellite free spectrum and allow unambiguous determine the oxidation state of a Ni/Co/Mn alloy.
Application Note on the reduction in preferential sputtering of TiO2.