Mass solid probe

Because an increase in resolution causes a decrease in sensitivity, it is best to operate at the lowest resolution commensurate with good results. Some instrument data systems will allow calibration with an external reference material such as perfluorokerosene and then use of a secondary reference material for the internal mass reference. Tetraiodothiophene, vaporized using the solids probe inlet, is recommended as the secondary reference. The accurate masses are 79.9721, 127.9045, 162.9045, 206.8765, 253.8090, 293.7950, 333.7810, 460.6855, and 587.5900. For a higher mass standard, use hexaiodobenzene. Because the mass defect for these internal reference ions are so large, a resolution of 2000 is ample to separate these ions from almost any sample ions encountered in GC/MS. 

The range of compounds from which electron ionization spectra may be obtained using the particle-beam interface is, like the moving-belt interface, extended when compared to using more conventional methods of introduction, e.g. the solids probe, or via a GC. It is therefore not unusual for specffa obtained using this type of interface not to be found in commercial libraries of mass spectra. 

The main features of DCI-MS and DCI-MS/MS are given in Table 6.14. DCI has gained rapid popularity because it is relatively simple to adapt to almost any mass spectrometer and gives results similar to FD, but in a more simple manner. It is not a substitute for FD, but it is less expensive and generally produces more fragmentation information than FD. For many compounds, molecular ions will be obtained where conventional solids probes would not do the job. DCI is known for the specificity provided by choosing reagent gas with different proton affinities. The major... 

State-of-the-art ToF-MS employs reflection lenses and delayed extraction [176] to improve resolution by minimising small differences in ion energies, and in these cases up to 12000 mass resolution (FWHM, m/z 600) is available. This is sufficient for most modern applications. Solid probe ToF-MS (or direct inlet high-resolution mass spectrometry, DI-HRMS) is a breakthrough. DIP-ToFMS is a thermal separation technique. Advantages of DIP-ToFMS are ... 

Direct solid-state polymer/additive mass analysis has involved various ionisation modes El (Section 6.2.1), Cl (Section 6.2.2), DCI (Section 6.2.2.1), FAB (Section 6.2.4), FI (Section 6.2.5), FD (Section 6.2.6) and LD. Survey mass spectra obtained with soft ionisation methods (FI-MS, CI-MS) provide diagnostic overviews of chemical composition. The supplemental tandem (MS/MS) and atomic composition (AC-MS) techniques are used to make specific identifications of various organic ingredients. Direct analysis of polymer systems for more than a few thousand daltons has only just begun. Ionisation methods employed are FD, ESI and MALDI. Solid-probe ToF-MS (or DI-HRMS) is a breakthrough [188]. 

Mass spectrometry combines exquisite sensitivity with a precision that often depends more on the uncertainties of sampling and sample preparation than on those of the method itself. Mass spectrometry is a supreme identification and recognition method in polymer/additive analysis through highly accurate masses and fragmentation patterns quantitation is its weakness. Direct mass spectrometry of complex polymeric matrices is feasible, yet not often pursued. Solid probe ToF-MS (DI-HRMS) is a breakthrough. Where used routinely, mass spectrometrists are usually still in charge. At the same time, however, costs need to be watched. 

Figure 8. Accurate mass chromatograms—CI(CH,) analysis (solids probe) of an ambient filter spiked with H,SO and ammonium sulfate salts...

Figure 12. Class searches from solids probe analysis of ambient filter samplenegative ion CI(CH ) accurate mass fragmentograms...

Many manufacturers now offer other sample injection systems compatible with the vacuum lock used for the solids probe. These include small (e.g., 75-ml) heatable batch inlet systems, usually accessible via syringe (gas syringe or GC microliter syringe for liquids), which can be particularly useful as inlets for mass reference compounds. Other probes are designed as flexible, easily removed connections to a gas chromatograph via some form of interface. 

The electron impact ionization mass spectrum of cortisone acetate was obtained using solid probe introduction, using a Shimadzu QP-Class-5000 gas chromatography mass spectrometer system. The most prominent ions observed, and their relative intensities, are shown in Table 6. 

Tetrakis(acetato)ditungsten(II) is a very air-sensitive, bright yellow, diamagnetic solid. It is moderately soluble in THF and acetonitrile but solutions in the latter solvent decompose after several hours. The 360 MHz XH NMR spectrum (in THF-d8) consists of a single methyl resonance at S 2.91. The mass spectrum (solid probe, electron impact, 40-70-eV ionizing voltage) shows the parent ion multiplet at m/e 604. Other spectroscopic data and physicochemical properties are described in the literature.8... 

Deactivated catalysts (5.4-5.5 mg) were loaded at ambient conditions into a 0.1 cm id X 2.0 cm quartz tube having one sealed end. Catalyst was held in place with a plug of Amersil quartz wool. Both quartz wool and tubes were baked out at 500°C for one hour prior to use. The loaded tube was placed into the electrically heated tip of the solids probe of a DuPont model 21-491 mass spectrometer operated at 1 X 10 7 torr. The solids probe was located in the mass spectrometer so that its tip, through which desorbing hydrocarbon molecules passed, was immediately adjacent to the ion source. The probe temperature was raised from 38° to 385°C in 22 minutes. Spectral scanning was conducted automatically every 30 seconds from approximately mje 16 to ra/e 650 at 10 sec/decade. 

Figure 8. Comparison of solids probe mass spectra obtained from extract at 825° C and by desorption at 816° C of parent H-mordenite deactivated with...

Species Inside Deactivated Catalysts. The total extract of the adsorbate in deactivated parent H-mordenite was heated using the solids probe of the mass spectrometer. Intense fragment ions at the higher m/e values, previously not observed to be of such intensity in the dynamic de-... 

The following discussion will be concerned primarily with applications of the ms/ms technique in the synfuel area. Attempts will be made to illustrate the unique capabilities of the ms/ms analysis with examples taken from our work on coal liquefaction products. Figure 5 shows the positive ion chemical ionization (PCI) mass spectrum of the coal liquid in question (SRC II mid heavy distillate, total bottoms). This spectrum is actually the normalized sum of approximately 500 individual mass spectra taken while the SRC II was thermally vaporized from a solids probe into the source of a mass spectrometer, and represents the molecular weight profile of this distillate fraction. Since isobutane Cl gives to a first approximation only protonated molecular ions (and no fragment ions), the peaks represent the individual components in the SRC II arranged incrementally by molecular weight. 

Despite these difficulties the use of the silica gel technique for the solid probe/quadrupole mass spectrometer system holds promise for the analysis of some nutritionally important metals Both zinc and copper have been extracted successfully from serurn and zinc has also been extracted from urine and feces by using an anion exchange purification Biorad A61X8 (100-200 mesh) chloride form) anion exchange resin has been used to separate copper and zinc from acidic solutions (6) We have adapted this method to the separation of these two metals from acidic solutions of AAS standards urine serum and deproteinated fecal homogenate by elution with sucessively dilute acid solutions Recovery of an isotopic spike ai subsequent mass spectral analysis has been demonstrated with a Zn spike added to 1ml aliquots of a Fisher Certified AA Standard (zinc concentration Img/ml) Results of this experiment are shown in Table III ... 

Mass spectrometry of zinc Isotopes has been realized using either chelates on a solids probe(10,11,17) or thermal Ionization of purified solutions(12). Both of these approaches require a chemical separation of all of the metals and this separation must be accomplished In an environment free of contamination from the metal(s) of Interest In the part-per blllion range (19). Neutron activation also requires a set of separation steps. In this case the requirement for a contamination-free environment Is the same but the chemical separation Is mainly to remove sodium and chlorine (2). 

The first pump removes air at a rate of 500 1/min and the second at about 300 1/min. The pressure in the first vacuum-lock is maintained at about 1 to 20 torr and that in the second about 0.1 to 0.5 torr. As a consequence the mass spectrometer source can be easily operated at about 10 torr. Flash vaporization of the solute occurs by radiant heating in a small chamber that butts directly onto the solid probe entrance to the ionization chamber and the vapor passes through a small hole directly into the ion source. The flash heater is either a nichrom coil or a quartz heater tube. The slots in the vacuum-locks are made of sapphire strips. An example of the use of the belt interface to monitor the separation of a pesticide mixture is shown in figure 20. 

Solid-probe mass spectrometric analysis (31) showed that the benzene-ether extracts consist mainly of organic acids. Therefore, these extracts were deriva-tized with dimethylsulfate-de to yield methyl-da-labeled derivatives. The derivatives were analyzed by GCMS and high resolution MS using techniques that have been described previously (31). Authentic samples of phenolic acids deriva-tized with dimethylsulfate-dg or diazomethane were also analyzed by GCMS for reference. The distribution of the organic acids as methyl esters was determined by measuring areas of GC fiame ionization detector peaks with a correction for the effective carbon number for each compound. 

The electron impact ionization spectrum of sulfacetamide was obtained at 70 eV using a solid probe insertion and is shown in Figure 5. The spectrum was run on a Finnigan Mat 112S double focusing mass spectrometer connected to a PDP 11/34 (DEC) computer system. It shows a molecular ion peak M+ at m/z 214. Since the molecule contains one sulfur atom, M+2 peak appears at m/z 216. The proposed fragmentation pattern and prominent ions are given in Table IV. 

Although mass spectrometers are of widespread utility, it is also important to understand their limitations. Particular instruments are usually designed and dedicated to a narrow range of tasks dictated by their linkage to specific modes of sample presentation (e.g., solids probe, liquid chromatograph, gas chromatograph, or a proton transfer reaction drift tube) and methods of ionization (e.g., electrospray or electron impact). A well-equipped MS laboratory will therefore contain a variety of instruments with different capabilities. 

After concentration, this extract was examined by EIMS using a heated solids probe. The probe was heated from ambient to 500CC at 50°C min whilst the VG AutoSpecE mass spectrometer was scanned from 950 to 25 amu at 5 s per decade in El mode at low resolution. The sample was also analysed using the standard GC-EIMS conditions. The TLC plate was left on the bench for 2 days, at which point all of the spots had changed colour to match the darkest spot. 

Li, N., Assmann,)., Schuhmann, W., and Muhler, M. (2007) Spatially resolved characterization of catalyst-coated membranes by distance-controlled scanning mass spectrometry utilizing catalytic methanol oxidation as gas-solid probe reaction. Analytical Chemistry, 79 (15), 5674-5681. 

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