Selected ion mode

Using MS detection relaxes the constraints on LC resolution, because additional separation occurs in the mass domain. In principle, LC-MS may yield a complete 2D distribution of a polymer according to chemical composition and molar mass. If MS detection is employed, the efficient cleaning in the LC step makes it possible to use total ion monitoring and even to identify unknown compounds from the sample. As extracts often contain interfering compounds, mass spectrometry in selective ion mode is a practical detector. Fully automated multidimensional LC-MS-MS-MS systems are available. 

Capillary columns may provide the best method for the separation of phenols prior to their quantification (Eichelberger et al. 1983 Shafer et al. 1981 Sithole et al. 1986). Of the various methods available for detection, the two commonly used methods that are most sensitive are mass spectrometry and flame ionization detection. Although electron capture detectors provide good sensitivities for higher chlorine-substituted phenols, they are poor for phenol itself (Sithole et al. 1986). The best method for the quantification of phenol may be mass spectrometric detection in the selected ion mode, but the loss of qualitative information may be significant (Eichelberger et al. 1983). 

B.A. Tomkins and G.A. Sega, Determination of thiodiglycol in groundwater using solid-phase extraction followed by gas chromatography with mass spectrometric detection in the selected-ion mode, J. Chromatogr. A, 911, 85-96 (2001). 

Detection atmospheric pressure chemical ionisation (positive or negative mode), selected ion mode. 

Jansson et al. [52] developed a low resolution method for PCA analyses, based on GC/ECNI-MS in the selected ion mode (SIM). In this method, PCAs were selectively removed from other common environmental contaminants by GPC, and quantification was performed by integrating the response of the Clj (m/z 70) ion, an ion that predominates in the mass spectra of individual PCA congeners at high ion source temperatures [54]. 

These experiments were undertaken in a similar manner to those described by Brady and Sanders for measuring relative binding affinities of metals with steroid derivatives by ESI-MS. Titrations with zinc and copper solutions were carried out on patellamides C and A by sequential addition of 0.25 equivalents of the metal solutions to the peptides (cone. 0.02 mg/mL in MeOH). These titrations were monitored by measuring the formation of the metal species as well as the loss of the uncomplexed peptides, using both the full spectrum and the selected ion mode of the instrument in parallel, as the ionisation efficiency of these species were very different. Once fully complexed zinc species were obtained for each peptide, copper solution was then titrated into these at a rate of 0.25 equivalents to again observe the competition effects. 

GC/MS is a powerful tool for identihcation and confirmation of the various components of olive oil. With GC/MS in the selective ion mode, unresolved GC peaks can be identified and accurately quantitated. For example, an apparent p-sitosterol peak in the sterol fraction was resolved into clerosterol (m/z 218) and A-5-avenas-terol (m/z 314), and both sterols measured regardless of inadequate GC resolution. 

An example of the sensitivity range which can be achieved by GC-MS is illustrated by the detection and semiquantitative determination of N-e-monomethyllysine and lysine in myosin hydrolysates isolated from heart cultures [159]. There are 620 residues of lysine to one of methyl-lysine in myosin. Operating in the selected ion mode these two compounds as their TFA-butyl derivatives can be estimated in a single run of injected sample from 4pmol of myosin. 

We have already made the point that the chromatogram carries a much higher information load than the absorbance value - this is certainly true for molinate which chromatographs well and responds with high sensitivity to both N- and S- selective GC detectors and to GC-MS in the selective ion mode. 

Were matrix interferences present Was the analytical instrument blind to interferences (e.g., GC/MS under selected ion mode) or was sample clean-up effective Is a different method of analysis going to be used from that published If so, will the solvent used for elution still be effective in the new instrumental method ... 

Detection by HP-MSD Model //5970B was in the selective ion mode at 166 M/E and 194 M/E for Z-9-DDA and Z-ll-TDA, respectively. Corresponding retention times were 17.7 and 22.7 min. Sensitivity was <5 ppb for both materials at 80% recovery. Insect control by this biotechnical approach was good, and it eliminated the use of traditional chemical pesticides against grape berry moth. 

Quantitation was with a Hewlett-Packard Model 5970B Mass Selective Detector run in the SIM (Selective Ion Mode) at the major unique M/E for each compound. Retention times of 17.7 min and 22.7 min were recorded for Z-9-DDA (M.W. 198) and Z-ll-TDA (M.W. 254), respectively. Recoveries and sensitivities are found in Table II. Figure 1 illustrates the SIM response for standard materials, while Figures 2 and 3 are of a check material, and a check spiked with pheromone at the 5 ppb level. Figure 4 demonstrates the absence of... 

Jansson et al. (1991) developed a low resolution ECNI-MS method in the selected ion mode (SIM) [59]. CPs were first selectively removed from other potential interferences by GPC and detection was based on the response of the CI2 miz 70) ion. As noted earlier, this ion dominates the ECNI mass spectrum of individual CP congeners at high mass temperature [60]. 

In recent several years, many EPA and ASTM methods have been modified (such as the modified EPA method 8015, 8260 and 8270 and the modified ASTM methods 3328-90, 5037-90 and 5739-95) to improve specificity and sensitivity for measuring spilled oil and petroleum products in soils and waters by environmental chemists. For example, EPA Method 8270 has been modified to increase analytical sensitivity and to expand the analyte list to include petroleum specific compounds such as the alkylated PAHs, sulfur, and nitrogen containing PAHs, and biomarker triterpane and sterane compounds. The principal modification to EPA Method 8270 is the use of the high resolution GC-MS selected ion mode (SIM) analysis that olfers increased sensitivity relative to the full scan mode. Many environmental laboratories have used the modified EPA Method 8270, combined with column cleanup and rigorous QA measures, to identify and quantify low levels of hydrocarbons. 

The GC-MS analysis is conducted by injection of 1 /xL of FI orF2 into a gas chromatograph-mass spectrometer. The MS detector is operated in the scan mode to obtain spectral data for identification of components and in the selected ion mode (SIM) for quantitation of target compounds. An appropriate temperature program is selected to achieve near-baseline separation of all of the target components. Quantitation of the alkalized PAH homologues, other EPA priority PAHs and biomarker compounds are performed by the internal standard method with the RRFs for each compound determined during the instrument calibration. The ions monitored for alkylated PAH and biomarker analyses are listed in Table 27.4 and Table 27.5, respectively. 

It is very useful to quantitatively determine the amounts of compound released from single beads. The CLND, ELSD, and NMR methods are not applieable for the subnanomole amounts of sample released from single beads, so these measurements will need the more sensitive UV or MS detectors. For single eompounds an LC/MS run in selected ion mode is an extremely sensitive and speeific analytical method. 

For rapid scanning of GC output and to maximize sensitivity, mass analyzers are normally operated in selected ion mode, where only a few pre-selected ions are monitored at any one time. Electron ionization at 70 eV is normal although increased response has been observed in some systems using helium carrier gas when operated at lower ionization energies (10-20 eV). There is a growing interest in the use of negative ion chemical ionization as this technique is very sensitive to certain halocarbons, notably those containing bromine or iodine. 

QqQs have attained their workhorse status in quantitative analyses due to their unique combination of ruggedness and rehabUity, data acquisition rate, duty cycle (fraction of total operating time spent measuring the ions of interest in selected ion modes) and tandem MS capabilities, notably the ability to perform multiple reaction monitoring (MRM), also called selected reaction monitoring (SRM). 

Identification Based on the Viking GC/MSD. The VIKING GC/MSD will sample the vapors of the Munitions Treatment Vessel (MTV) of the MMD-1. The VIKING GC/MSD analysis is performed in selective ion mode (SIM). The SIM mode designates the ions of interest for each chemical agent being monitored. The ions used in the SIM analysis for the MMD-1 test are as follows ... 

The sensitivity and selectivity of GC-MS was used for the development and validation of a novel analytical method for the rapid and simultaneous detection of scopolamine and atropine in buckwheat Fagopyron esculentum) samples and related food products [98]. Low detection and quantification limits were achieved in the selected-ion mode (SIM) by derivatization (silylation) of the analytes. The LOD for atropine and scopolamine were found to be 0.3 and 1 pg kg, respectively, while the LOQ were 1 and 6 pg kg , respectively, which corresponds to less than one D. stramonium seed per million buckwheat fruits. 

Most of the GTI detection and quantitation must be done by HPLC/MS or GC/MS using a selective ion mode. " MS gives the greatest opportunity to rule out interference that may occur using HPLCAJV and GC/FID detections thus, HPLC/UV or GC/FID detection must always be assessed as an alternative. Lui et al. demonstrated the development of a hyphenated MS-based analysis to control the level of GTIs for a pazopanib process. The LC/MS techniques were not robust enough to transfer to QC laboratories. By setting proper controls of GH impmities upstream in the process, HPLC/UV could be used for the analysis. This made the methods more suitable for transfer to a QC lab. 

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