SIM method

Although detailed methods depend on the instrument used, sources and ionization method are the major difference between SIMS and TIMS methods. SIMS methods... 

The Surflex-Sim method operates significantly differently [104]. Each of the molecules is surrounded by a set of observer points that characterizes the local character of the surface and potential interactions. Two similar molecules will have a common subset of comparable observer points. A optimal alignment occurs when the differences in pharmacophore character and molecular surface inferred from the observer points are minimized between two molecules. To speed up the algorithm, large molecules can be fragmented into parts which are then compared, and then tested for consistency. This feature also makes the method capable of identifying alignments when one molecule is much smaller than the other. 

The impact of an ion beam on the electrode surface can result in the transfer of the kinetic energy of the ions to the surface atoms and their release into the vacuum as a wide range of species—atoms, molecules, ions, atomic aggregates (clusters), and molecular fragments. This is the effect of ion sputtering. The SIMS secondary ion mass spectrometry) method deals with the mass spectrometry of sputtered ions. The SIMS method has high analytical sensitivity and, in contrast to other methods of surface analysis, permits a study of isotopes. In materials science, the SIMS method is the third most often used method of surface analysis (after AES and XPS) it has so far been used only rarely in electrochemistry. 

In order to detect possible impurities or doping agents at rather low concentrations the SIMS method should be chosen. Compared to XPS the detection limit of SIMS is... 

Special equipment required Column chemistry limited Carry-over Viscous heating Detection at low wavelength (blending noise) Increased care due to high pressure Rapid SIM method development Isomer separation SIM with highest complexity Separations with challenging matrices, e.g. LFCs... 

The last few years have shown increasing applications of TOF-SIMS in forensic science. Preliminary studies in the visualization and analysis of fingerprints indicate that the TOF-SIMS method opens new perspectives for the examination of fingermarks, especially in the imaging of fingermarks in various ions. 

Dynamic recovery, 2 330 Dynamic reversibility of noncovalent interactions, 24 61 Dynamic scattering device, 15 115 Dynamic sealing, for pumps, 21 81-82 Dynamic SIMS method, 24 107-108 Dynamic uncertainties, 26 1019, 1021-1023... 

Static SIMS method, 24 107, 108 Static uncertainties, 26 1019-1021 Statins, 2 821-822, 5 137, 138-140t, 142-143... 

Pb UPD on polycrystalline An electrode in 0.1 M perchloric acid solution has been studied by Henderson et al. [484]. In this study, CV, electrochemical quartz crystal microbalance (EQCM), and probe beam deflection methods have been used. It has been found that Pb UPD proceeds in three steps. The first step comprised water ejection from the gold surface. This step was followed by metal UPD accompanied by the removal of the adsorbed OH. Also, Zeng and Bruckenstein have studied UPD and adsorption of Pb on pc-Au electrodes, applying XPS and TOF-SIMS method in case of 0.1 M NaCl electrolyte [485], and EQCM in case of 0.1 M NaCl04 and 0.1 M NaCl electrolytes [486]. In the presence of chloride anions, the adsorption of Pb—Cl complex has been found. 

A new gas chromatography (GC) method was developed to characterize artemether 28a and its metabolites in body fluids. The extracts were derivatized and then separated on an optimized capillary GC system and identified by chemical ionization MS using ammonia as the reagent gas <1998JCH(B)101>. A sensitive, selective, and reproducible GC-MS-SIM method has also been developed for the determination of artemether 28a and dihydroartemisinin 29a in plasma, using artemisinin 9a as an internal standard <1999JCH(B)251>. 

Table 3.1.5 Analyte concentrations for the calibration curve used in the GC-MS SIM method. ISTD Internal standard...

Table 3.1.9 Acquisition windows and ion species monitored by the GC-MS SIM method. The window start times may vary slightly and are column and instrument specific ... 

Quantitative Analysis. The derivatization/SIMS method can also be applied quantitatively. For example, two ketones, acetone and dg-acetone, were mixed in various concentrations in the range of 0.1 to 10 mg/mL and in the ratios of dg/dg = 10/1, 1/1,... 

Ion beams provide useful information either as a diagnostic tool or as a precision etching method in adhesion research. The combination ISS/SIMS method used along with other techniques such as SEM provides a powerful tool for elemental analysis of surface composition. These results, as well as earlier work in this laboratory, indicate that the surface composition can be significantly different from the bulk due to contamination, selective chemical etching and segregation. These same techniques also provide an analysis of the mode of failure in adhesive joints. Many failures classified as "adhesive" on the basis of visual inspection are frequently mixed mode failures or failures at a new interface containing elements of both adhesives and adherend. 

Kovarsky et al have used the SIMS method to determine the mole fraction in InGaN [8], Their technique is based on a comparison of the relative signal intensities of CsM+ (M = In, Ga) and does not require reference samples. The SIMS results were independently confirmed by XRD, energy dispersive X-ray fluorescence spectroscopy, EPMA and SNMS, and the absolute value of the InN mole fraction has a relative accuracy <15%. 

Robinson, J.R. and M. Sims Method and System for Extracting a Solute from a Fluid Using Dense Gas and a Porous Membrane U S, Patent 5,490,884 February 13, 1996. 

In essence, any steroid can be estimated by SIM methods as long as a suitable derivative and an adequate internal standard are available. However before embarking on such a procedure, the analyst must be convinced that a particular assay cannot be usefully made by a cheaper and faster method. Although GC-MS has a great range of specificity and adequate sensitivity, both of which make the development of an assay... 

Figure 1.23. The identification of the herbicide paraquat, as its reduction product, in the post-mortem bile of a murder victim using SIM methods. Arrowed points indicate channel offset and correspond to the elution time of the authentic substance. M/M-2 (m/e 192 m/e 190) ratios at, A, source temperature 280°C and B, source temperature 205°C were consistent with those in the authentic compound C. represents a control bile extract [502]...

Neurosteroids are steroids that are synthesized de novo in the central nervous system (androsterone, dihydrotestosterone, testosterone, allopregnanolone, isopregnanolone, and pregananole). After extraction of plasma and cerebrospinal fluids, using solid-phase extraction (SPE), and derivatization with carboxymethoxime, pentafluoro-benzyl, and trimethylsilyl, the derivatized samples were injected into a GC-MS system for quantitative evaluation with a selected ion monitoring (SIM) method. Details of the method have been described in Ref. [25]. 

The MS/MS spectra extracted from the SI run just described also serve as the basis for automatically generating the quantitative SRM methods for these compounds. The most intense product ion from the full-scan MS/MS spectra obtained under the different ionization modes is selected for the SRM transition, and the method is automatically written in that ionization mode. The software approaches this method development procedure as an actual analyst would. SRM transitions that involve a simple loss of water or ammonia are not favored. If an SRM transition of suitable intensity cannot be obtained, then a SIM method is created instead. The [M -+ H]" " or [M — H] ion is favored for SIM. If these ions are not present above a user-defined threshold, then the software can create a SIM method that monitors an adduct. The SI method incorporates multiple scan types across LC peaks where the concentration of the analyte of interest rapidly changes. This rapid change in concentration presents a problem of how to determine which mode of operation and ions... 

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