Speciation analysis of oxides with static secondary ion mass spectrometry.

Speciation analysis of inorganic solids, without dissolution of the sample, aims at specific molecular information. Two potentially useful microanalytical techniques emerge, namely, laser microprobe mass spectrometry (LMMS) and static secondary ion mass spectrometry (S-SIMS). This paper focuses on the molecular characterisation of oxides by application of the S-SIMS method. For this purpose, mass spectra of pure oxides were acquired under static conditions. Analytical parameters such as repeatability, accuracy and resolution were assessed. Also, the peak patterns in the mass spectra are discussed in connection with the older Plog model, describing the relative ion yield as a function of the cluster size. Finally, a comparison is made with the mass spectra from a S-SIMS library and with those obtained by Fourier transform LMMS. Copyright 1999 John Wiley & Sons, Ltd.

Automated Particle Analysis of Populations of Silver Halide Microcrystals by Electron Probe Microanalysis under Cryogenic Conditions.

An automated particle analysis routine is implemented on an electron microprobe for analyzing the chemical composition and projective area of populations of individual silver halide microcrystals. An LN2 cryostage is used to prevent material degradation due to reaction with the impinging electron beam. The background in the EDX spectra is lowered by depositing the microcrystals on a carbon-coated copper grid, mounted in a transmission holder. The ILα/AgLα net X-ray intensity ratio, obtained from a spectrum-fitting algorithm, is used to determine the crystal composition by means of a standard-based calibration curve. The uncertainty on the concentration measurement of individual microcrystals is calculated using the uncertainties on the net X-ray counts and the uncertainties on the calibration curve. The area measurement is optimized by introducing a gray value histogram correction on each individual measurement. Overlapping microcrystals are scrapped from the analysis by defining a maximum shape factor, against which the shape factor of the microcrystal is tested. To minimize problems with drift of the cryostage, spectrum acquisition is carried out immediately after a single microcrystal has been located, based on the backscattered electron image. Several applications are discussed.

Acquisition and quantification of ion images with a camera-based detection system and classical quantification algorithms.

The quantitative analytical characteristics of a camera-based detection system for secondary ion microscopy are studied in detail. Through multiple exposures, ion images with large dynamic ranges are obtained. The quantification of these images by the sensitivity factor method and the matrix ion species ratio method is described and evaluated by the analysis of steel and aluminum standard reference materials.

On the use of laser microprobe mass spectrometry for the analysis of organic biomolecules.

Laser microprobe mass spectrometry has been applied to a variety of organic polyfunctional molecules, covering a wide range of polarity and mass spectrometric behaviour. The technique apparently combines desorption under relatively soft conditions with extensive fragmentation and hence allows much structural information from intactly released thermolabiles to be obtained. The mass spectra appear unfamiliar in comparison to conventional techniques. Interpretation is attempted in a purely empirical way by means of the evidence from our database and tentative hypotheses to rationalize the desorption and ionization by laser microbeam irradiation of organic solids. Selected examples are presented to illustrate the potential and limitations of the method in the field of biomolecules, such as pyridoxine and pyridoxal phosphate, nucleosides, nucleotides and related analogues, drugs and the corresponding N-oxides.

Structural characterization of drugs and oxygenated metabolites by laser microprobe mass spectrometry (LAMMA).

Laser microprobe mass analysis (LAMMA) was used for the structural characterization of polyfunctional drugs and their oxygenated metabolites, in particular the N-oxides. The spectra usually yield the molecular weight as well as intense fragments. The structural information is characteristically distributed between the positive and negative ions. To rationalize the unfamiliar fragmentation, tentative pathways are introduced. Key elements are the formation of odd-electron molecular (and fragment) ions, the correlation between cations and anions, as well as the three-dimensional representation of structures. The combination of mild desorption and abundant fragmentation makes LAMMA a valuable tool in the study of N-oxides.

In-depth limitation of the Lamma 500 for the in situ localization of organic compounds in biological embedded tissue samples.

The objective of this study was exploration of the potential, offered by the laser microprobe mass spectrometer (LAMMA), for the in situ localization of organic targets in embedded tissues by means of structurally relevant ions. A series of model systems was designed to evaluate stepwise the analytical problems involved. A preliminary screening pointed to the position of the target in comparison to the actual sample surface as a determining parameter. Refined simulations were carried out with sandwich samples, consisting of an epon carrier (thickness 1 micron), coated with microcrystalline targets and covered with a layer between 5 and 50 nm of different materials (epon, carbon, formvar). In addition to the stimulated conversion of molecular into fragment ions, the presence of a barrier leads to a drastic loss of sensitivity (20-50 x) and unacceptable degradation of the mass spectrometric quality (resolution, calibration).