SIM mode

Determination of C -C cai bonyl compounds, phthalic acid alkyl esters, mutagen MX and its geometric isomer E-MX, chlorophenols, organochlorine pesticides (OCPs) - a-, P-, J-, 5-HCH, DDE, DDD, DDT, total isomeric-specific content of polychlorinated byphenyls (PCBs) (tri-, tetra-, penta-, hexa-, hepta-, octachloroisomers) in SCAN and SIM mode was canned out. MDE of procedure for OCPs makes up 0.01-0.1 and PCBs - 0.17-0.38 ng/1 at enrichment factor K = (1.50-4.00)T0. ... 

To determine the residue levels of dinitroaniline herbicides, GC/NPD or GC/ECD is used in general. An aliquot of GC-ready sample solution is injected into the gas chromatograph under the conditions outlined below. Further confirmatory analysis is carried out using gas chromatography/mass spectrometry (GC/MS) in the selected-ion monitoring (SIM) mode. 

GC/MS in the SIM mode was carried out for confirmation of all positive and ambiguous results obtained from GC analysis. GC/MS was effective as a multiresidue screening method for crops the mean recovery of trifluralin from green bean, cilantro, apple, tomato, and green onion at a fortification level of 0.25 mg kg was 55% and the LOD was 0.05 mg kg . ... 

Specificity is unsurpassed. Traditionally, MS was performed on very large and expensive high-resolution sector instruments operated by experienced specialists. The introduction of low-resolution (1 amu), low-cost, bench-top mass spectrometers in the early 1980s provided analysts with a robust analytical tool with a more universal range of application. Two types of bench-top mass spectrometers have predominated the quadrupole or mass-selective detector (MSD) and the ion-trap detector (ITD). These instruments do not have to be operated by specialists and can be utilized routinely by residue analysts after limited training. The MSD is normally operated in the SIM mode to increase detection sensitivity, whereas the ITD is more suited to operate in the full-scan mode, as little or no increase in sensitivity is gained by using SIM. Both MSDs and ITDs are widely used in many laboratories for pesticide residue analyses, and the preferred choice of instrument can only be made after assessment of the performance for a particular application. 

LC/MS is used as a multi-residue analytical method. The recovery of imidacloprid from tomato was 90-105% for 0.05 and 0.5mgkg . The LOD for imidacloprid was < 10 pg kg in the full-scan mode and 1 pg kg in the selected-ion monitoring (SIM) mode. ... 

High sensitivity (low pg levels in PCI scan mode 1 fg in NCI SIM mode)... 

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. 

Figure 9.1 GC MS chromatograms acquired in the SIM mode of a laboratory blank (a) and an amino acid standard solution with concentrations at the quantitation limit (b). i.s.l, Hexadecane internal standard i.s.2, norleucine internal standard...

Figure 9.1a reporting GC-MS results taken on laboratory blank in a GC-MS procedure [87] shows negligible amino acid contamination. Indeed, quantitating a protein as the sum of 14 amino acids, a value of about 200 ng is the minimum required threshold to positively consider the protein identification. Figure 9. lb reports the chromatogram of an amino acid standard solution acquired in the SIM mode and corresponds to the quantitation limit that is a content of about 700 ng in the sample at a confidence level of 95%. This seems amenable when working at the trace level. 

Analysis of dyed fibres allows identification of real colouring components of natural dyestuffs taking part in the dyeing process. Wool threads dyed with madder (Rubia tinc-torum) as well as Our Lady s bedstraw (Galium verum), were studied by HPLC DAD ESI MS" (SIM mode).[8] Chromatograms of the extracts from wool dyed with madder... 

Isotope dilution gas chromatography-mass spectrometry has also been used for the determination of ppb of total chromium in seawater [181-183]. The samples were reduced to ensure Cr111 and then extracted and concentrated as tris (l,l,l-trifluoro-2,4-pentanediono) chromium (III) [(Cr(tfa)3>] into hexane. The Cr(tfa)2 mass fragments were monitored into a selected ion monitoring (SIM) mode. 

Fig-1 SPE-LC-ESI-MS analysis (SIM mode) of two wastewater samples, spiked at different levels of concentration. Compounds (1) ciromazine, (2) oxamil, (3) metomil, (4) carbendazime, (5) thiabendazole, (6) imidacloprid, (7) acetamiprid, (8) thiacloprid... 

Fig. 2.6. Chromatogram showing the simultaneous analysis of 16 PAHs (A), 7 chlorobenzenes (B), 10 organochlorine pesticides (C), and 7 PCBs (D). Column RapidMS (10 ml x 530 jim i.d., 0.12 pm df, Varian, The Netherlands. GC oven 50°C (lmin) to 190°C (3 min) at 30°C/min to 280°C at 40°C/min. MS time-selected SIM mode with dual ion confirmation. Analyte concentration levels were between 50 and 175 ppb [38].

The problems relating to increased contamination levels and/or insufficient sensitivity may be overcome by using matrix-solid phase dispersion, MS detection in selected ion monitoring (SIM) mode, and/or large volume injection. An example of combined analysis that utilizes specific detection is shown in Fig. 2.6. It entails simultaneous analyses of PAHs, PCBs, chlorobenzene, and organochlorine pesticides in soil. 

Fig. 2.1.2. Mass chromatograms in the SIM mode using protonated molecular ions of LAS trifluoroethyl esters, (a) LAS standard mixture and (b) LAS found in a sediment. Peak labels indicate the position of the benzene sulfonate moiety on the linear alkyl chain. Reproduced with permission from Ref. [18]. 1997 by American Chemical...

Tsuda et al. [16] determined NP and OP in bioaccumulation experiments with freshwater fish. The analytes were extracted with acetonitrile and the lipid in the sample extract was eliminated by partitioning between hexane and acetonitrile. After Florisil PR column clean-up, the sample extract was analysed by GC-MS in the SIM mode. 

The adduct formation can be largely controlled and directed into the formation of a single selected species by adequate choice of the ionisation mode (possibly at the expense of sensitivity), the eluent composition (buffer addition, pH adjustment, type of organic modifier) and by optimisation of the ion source parameters influencing the stability of individual (adduct) ions. In contrast to the variations in adduct or cluster formation, which principally can be diagnosed by recording more than one (adduct) ion in SIM mode, the occurrence of ion suppression requires more careful diagnosis. 

The operation of magnetic sector (Chap. 4.3), linear quadrupole (Chap. 4.4), or quadrupole ion trap (Chap. 4.5) mass spectrometers in the repetitive scanning mode is useful for the identification of the components of a mixture. If quantitation is a major issue (below), selected ion monitoring (SIM) is preferably employed the term multiple ion detection (MID) and some others are also in use. [33] In the SIM mode, the mass analyzer is operated in a way that it alternately acquires only the ionic masses of interest, i.e. it jumps from one m/z value to the next. [34-39] The information obtained from a SIM trace is equivalent to that from a RIC, but no mass spectra are recorded. Thus, the scan time spent on a diagnostically useless m/z range is almost reduced to zero, whereas the detector time for the ions of interest is increased by a factor of 10-100. [40] An analogous improvement in sensitivity (Chap. 5.2.3) is also observed. 

Example A potential drug and its metabolite in a liver sample are quantified by internal standardization with trideuterated standards for both compounds (Fig. 12.4). [25] Under these conditions it neither presents a problem that both analytes and their isotopic standards are almost co-eluting from the LC column, nor does the completely unspecific TIC play a role. If required for sensitivity reasons, this analysis could also have been performed in the SIM mode using the m/z values of the RICs shown. 

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