Instrumentation for SIMS

In its most elementary form, a SIMS system consists of a source of primary ions, a sample holder, secondary ion extraction optics, a mass spectrometer, and an ion detector, all housed in a UHV compartment. Systems are also equipped with data processing and output systems. A schematic diagram 

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Jede, R., Ganschow, O., Kaiser, U. (1992) Instrumentation for SIMS. In Practical Surface Analysis, edited by Briggs, D., Seah, M. Chichester, UK John Wiley Sons, pp. 19-104. 

Jede R, Ganschow O, Kaiser U (1992) Instrumentation for SIMS. In Briggs D, Seah MP (eds) Practical surface analysis volume 2— ion and neutral spectroscopy, 2nd edn. Wiley, New York... 

LC-PB-MS is especially suited to NPLC systems. RPLC-PB-MS is limited to low-MW (<500 Da) additives. For higher masses, LC-API-MS (combined with tandem MS and the development of a specific mass library) is necessary. Coupling of LC via the particle-beam interface to QMS, QITMS and magnetic-sector instruments has been reported. In spite of the compatibility of PB-MS with conventional-size LC, microbore column (i.d. 1-2 mm) LC-PB-MS has also been developed. A well-optimised PB interface can provide a detection limit in the ng range for a full scan mode, and may be improved to pg for SIM analyses. 

True profile analysis requires scanning over the whole mass range for the acquisition of all data on excreted compounds. Quantitation has been more challenging on a quadrupole instrument because total ion current peaks are seldom a single component and extracted-ion chromatograms (EICs) when recovered from scanned data are of poor quality due to the lower sensitivity of scanning GC-MS. Thus, we developed profile analysis based on SIM of selected analytes but tried to ensure the components of every steroid class of interest were included. For ion traps the fundamental form of data collection (in non-MS/MS mode must be full -scans). Thus, the quantitative data produced are EICs obtained from scanned data. The EICs are of the same ions used for SIM in quadrupole instruments and the calibration external standards are the same. 

A few SIMS and SNMS instruments for surface analysis187-189 are commercially available on the analytical market. These are SIMS instruments using a double-focusing sector field mass spectrometer (e.g., CAMECA IMS-7f), time-of-flight secondary ion mass spectrometers (ToF-SIMS IV from CAMECA, Cedex, France, or ToF-SIMS 5, the ToF-SIMS 300 from ION-TOF, Munster, Germany and the PHI TRIFT IV from Physical Electronics, USA) and quadrupole based SIMS (SIMS 4550 and 4600 CAMECA, Cedex, France) or the quadrupole based SNMS instruments with SIMS option (INA-X, SPECS GmbH, Berlin, Germany). 

Commercially available GC-MS systems present major differences in their detection and recording system. Many quadrupole instruments use SIM for the determination of analytes at trace levels. With this type of instrumentation, more than 1-10 ng of the analyte is required to record a full-scan mass spectrum. In contrast, instruments based on ion-trap technology can record a full-scan mass spectrum on an analyte at pg level. With SIM, a limited number of ions are monitored during a selected time interval of the chromatogram. The presence of the analyte is determined by the presence of these diagnostic ions at the correct retention time and in the correct abundance ratio (33). 

In 1949 Herzog and Viehbock reported a novel ion source for mass spec-trography (Fig. 4.2) [9]. This source provided separate accelerating fields for the primary and secondary ions and thus became the first modem instrument designed specifically for SIMS. The design included acceleration of the positive secondary ions from an equipotential surface through an electric field acting as an electron-optic lens. 

Mass spectral data shall be obtained using a low resolution instrument that utilizes 70 volts (nominal) electron energy in the electron impact mode. The system shall he capable of selected ion monitoring (SIM) for at least 18 ions per cycle, with a cycle time of 1 second or less. Minimum integration time for SIM is 25 milliseconds per m/z. The integration time used to analyze... 

Until recently, analytical investigations of surfaces were handicapped by the lack of suitable methods and instrumentation capable of supplying reliable and relevant information. Electron diffraction is an excellent way to determine the geometric arrangement of the atoms on a surface, but it does not answer the question as to the chemical composition of the upper atomic layer. The use of the electron microprobe (EMP), a powerful instrument for chemical analyses, is unfortunately limited because of its extended information depth. The first real success in the analysis of a surface layer was achieved by Auger electron spectroscopy (AES) [16,17], followed a little later by other techniques such as electron spectroscopy for chemical analysis (ESCA) and secondary-ion mass spectrometry (SIMS), etc. [18-23]. All these techniques use some type of emission (photons, electrons, atoms, molecules, ions) caused by excitation of the surface state. Each of these techniques provides a substantial amount of information. To obtain the optimum Information it is, however, often beneficial to combine several techniques. 

In mass spectrometric studies, WT have been applied mainly in two areas including secondary ion mass spectrometry (SIMS) and instrumentation design. SIMS is a type of surface technique for trace analysis, determination of elemental composition, and the identity and concentrations of adsorbed species and elemental composition as a function of depth [46]. The application of wavelet denoising techniques to SIMS images has been studied by Grasserbauer et al. [47-50], and details about these studies are presented in another chapter of this book. 

Secondary-ion mass speciromelry (SIMS) is the most highly developed of Ihe mass spectromelric surface methods, with several manufacturers offering Instruments for this technique. SIMS has proven useful for determining both Ihe atomic and the molecular composition of solid surfaces. ... 

Operation of a SIMS instrument resembles both that of an isotope ratio mass spectrometer and an electron microscope. Most SIMS instruments include an optical microscope so that the sample can be directly viewed during analysis, which allows for accurate positioning of the area of interest on the sample. Data can be in the standard mode used for other types of mass spectrometers in which ions are produced and the mass spectrum is analyzed by scanning or peak-hopping. This mode is sometimes called the microprobe mode in SIMS. Another application for SIMS is the acquisition of ion-images. This mode is called the microscope mode because the SIMS is operated as an ion microscope. 

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