SIM acquisition

Table 7.1 reports the ions commonly used in SIM acquisition for the quantification of trimethylsilyl (TMS) and f-butyldimethylsilyl (TBDMS) derivatives. 

FIGURE 24.5 Chromatogram (selected part) of red wine spiked with 500 ng/L of 2,4,6-trichloroanisole obtained after SPME extraction and simultaneous scan/SIM acquisition on a GC/MS system (7890A/5975C MSD, Agilent Technologies). (A) Total ion current (TIC) of scan run (rn/z = 33-233) (B) TIC of SIM run (m/z = 195,197,210) (C) ion abundances in SIM mass spectrum. Peak of 2,4,6-trichloroanisole on chromatogram B marked with an arrow. 

Prepare two replicates of sample (2 mL), add IS, and analyze the samples according to the procedure described in this unit. The chlorinated compound investigated (DCM, TCE, and PCE) and IS should be undetectable if not, check for contamination (see Sections 29.1.1 and 29.1.2). Additionally, no interferences should be detected at the same retention time as the substances investigated otherwise, there should be no fragment ions (m/z) in common with those selected for DCM, TCE, and PCE under selected ion monitoring (SIM) acquisition. 

Set up a SIM acquisition method using the retention times and the most abundant characteristic ions (see Table 29.3). Use the SIM method in all further experiments. 

Anthraquinoids (purpurin, munjistin) [154] Madder Greek painting materials, Hellenistic period (second to third century b.c.) and Roman period (second century a.d.) ESI operating in negative-ion mode, single qnadmpole analyzer with SIM acquisition mode... 

Theobromine, caffeine [148] Cacao APCI operating in positive-ion mode, single qnadmpole analyzer with SIM acquisition mode... 

Boros et al. [85] investigated the floral nectar of different Datura species as a potential source of intoxication. Atropine and scopolamine were quantified by HPLC on an Ascentis Express Cig column (50 x 2.1 mm) packed with 2.7 pm fused-coie particles and monitoring using the SIM acquisition mode by ESl-MS/MS detector. 

Two general modes of data acquisition are available in MS full-scan acquisition and selective ion monitoring (SIM). In full-scan analysis, a continuous series of mass spectra is acquired during the chromatographic run. For high-efficiency open capillary GC columns, sufficiently fast scanning is required in order to acquire a sufficient number of data points (typically 10 to 20) to adequately describe the chromatographic peak profile. However, in routine quantitative analysis of a limited number of components, better results in terms of lower detection limits are achieved by the use of SIM, in which the intensity of a (number of) ion(s) is monitored. The choice between full-scan and SIM acquisition in a particular application depends on the required detection limit and information content. 

Standard analyte Remark RT (min.) Ions selected for SIM acquisition Analyte number a ro... 

The described internal standard method is suitable for the quantification of more than 200 components, using a single-quadrupole GC-MS. The extraction process with acetonitrile is followed by a clean-up including a salting-out step and solid phase extraction. The compound detection is done by SIM using the retention time and selected ion abundance ratios as qualifiers for identification. Two runs are required to determine the complete set of pesticides given in Table 4.10 according to the required SIM acquisition windows described as FV-1 and FV-2. 

A database also allows instant access to the spectrum of a molecule by searching its name or CAS (Chemical Abstract Service) number. Suppose we must verify immediately that water has not been contaminated by toluene. We plan to use a GC-MS coupling device equipped with a quadrupole. The best way to proceed is by injecting toluene to determine its retention time (under the correct chromatographic conditions) and the main ions of its mass spectrum. One must then analyze the water (after liquid-liquid extraction with an organic solvent or directly by solid phase microextraction coupled with GC-MS) in SIM on the two or three main ions of toluene to reach a limit of detection that is as low as possible. If toluene cannot be injected in the laboratory, quick access to its El spectrum is available in databases. Ions for SIM acquisition will then be chosen from the reference spectrum. 

In quadrupole-based SIMS instruments, mass separation is achieved by passing the secondary ions down a path surrounded by four rods excited with various AC and DC voltages. Different sets of AC and DC conditions are used to direct the flight path of the selected secondary ions into the detector. The primary advantage of this kind of spectrometer is the high speed at which they can switch from peak to peak and their ability to perform analysis of dielectric thin films and bulk insulators. The ability of the quadrupole to switch rapidly between mass peaks enables acquisition of depth profiles with more data points per depth, which improves depth resolution. Additionally, most quadrupole-based SIMS instruments are equipped with enhanced vacuum systems, reducing the detrimental contribution of residual atmospheric species to the mass spectrum. 

Like XPS, the application of AES has been very widespread, particularly in the earlier years of its existence more recently, the technique has been applied increasingly to those problem areas that need the high spatial resolution that AES can provide and XPS, currently, cannot. Because data acquisition in AES is faster than in XPS, it is also employed widely in routine quality control by surface analysis of random samples from production lines of for example, integrated circuits. In the semiconductor industry, in particular, SIMS is a competing method. Note that AES and XPS on the one hand and SIMS/SNMS on the other, both in depth-profiling mode, are complementary, the former gaining signal from the sputter-modified surface and the latter from the flux of sputtered particles. 

To answer this question, we must consider the ways in which the data are acquired. An RIC is generated, post-acquisition, from consecutive full scans in which a small amount of time is spent monitoring each ion, as discussed above. The data produced in a SIM experiment are generated by monitoring only a small number of ions, thus taking advantage of the increased time spent monitoring each ion. 

GC-MS operated in electron impact (El) mode was only sporadically used for the determination of some UV filters such as 4-MBC, EHMC, and OC. Separation was achieved on a 60 m x 0.25 mm i.d. DB-5 column, with 0.25-pm film thickness. For quantification of the compounds, data acquisition was performed in selected ion monitoring (SIM) mode recording three characteristic ions per compound. GC-MS allowed the differentiation between the two isomers (cis/trans) for 4-MBC and EHMC. 

Positive results from the in vitro micronucleus test indicate that the test substance induces chromosome damage and/or damage to the cell division apparams, in cultured mammahan somatic cells. Immunochemical labehng (FISH fluorescence in sim hybridization) of kinetochores, or hybridization with general or chromosome specific centromeric/telomeric probes can provide useful information on the mechanism of micronucleus formation. Use of cytokinesis block facilitates the acquisition of the additional mechanistic information (e.g., chromosome nondisjunction) that can be obtained by FISH techniques. The micronucleus assay has a number of advantages over metaphase analysis performed to measure chromosome aberrations (see OECD TG 487 draft). 

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