Direct inlet mass spectrometry

Also, direct determination of additives by means of laser desorption in solid polymeric materials rather than in polymer extracts has been reported [266], Takayama et al. [267] have described the direct detection of additives on the surface of LLDPE/(Chimassorb 944 LD and Irgafos P-EPQ) after matrix (THAP)-coating. As shown in Scheme 7.13, direct inlet mass spectrometry is also applicable to transfer TLC-MS and TLC-MS/MS analyses without the need for prior analysis. For direct sample introduction a small amount of the selected... 

Case Studies Direct inlet mass-spectrometry (DI-MS)... 

In addition to GC/MS, high performance liquid chromatography (HPLC/MS) has been used to analyse natural resins in ancient samples, particularly for paint varnishes containing mastic and dammar resins [34]. A partial limitation of chromatographic techniques is that they do not permit the analysis of the polymeric fraction or insoluble fraction that may be present in the native resins or formed in the course of ageing. Techniques based on the direct introduction of the sample in the mass spectrometer such as direct temperature resolved mass spectrometry (DTMS), direct exposure mass spectrometry (DE-MS) and direct inlet mass spectrometry (DI-MS), and on analytical pyrolysis (Py-GC/MS), have been employed as complementary techniques to obtain preliminary information on the... 

CP/MAS NMR Cross polarisation/magic-angle DI-MS, DIMS Direct inlet mass spectrometry... 

Breimer, M. E., G. C. Hansson, K.-A. Karlsson, G. Larson, H. Leffler, W. Pimlott, B. E. Samuelsson, N. Stromberg, S. Teneberg, and J. Thurin Sequencing of Large Oligosaccharides by Direct Inlet Mass Spectrometry. Application to Cell Surface Glycolipids. Int. J. Mass Spectrom. Ion Physics. 48, 113 (1983). 

Kotiaho, T., Gylling, S., Lunding, A. and Lauritsen, F.R. (1995) Direct determination of styrene and tetrachloroethylene in olive oil by membrane inlet mass spectrometry. J. Agric. Food Chem., 43, 928-930. 

Li, X., Xia, L., Yan, X. Application of membrane inlet mass spectrometry to directly quantify denitrification in flooded rice paddy soil. Biol. Fertil. Soils 50, 891-900 (2014)... 

Riter et al. applied Membrane Inlet Mass Spectrometry (MIMS) coupled to a miniature mass spectrometer equipped with a cylindrical ion trap (CIT) analyzer to monitor the flavor components directly from human breath [6], Johnson et al. measured ethanol concentrations on-line in fermentation broths from a 9000-L fermentation reactor for a period of four days [7], However, data reported in the above papers referred to experiments lasting no more than a few days. 

Radicals can also be studied directly by mass spectrometry using a molecular beam inlet. It is difficult to design a satisfactory molecular beam probe and there are problems connected with the calibration of the spectrometer but a number of successful studies have been made (Foner and Hudson, 1954 Fristrom and Westenberg, 1965 Homann et al, 1963). 

Marai, L., Myher, J. J. and Kuksis, A. (1983) Analysis of triacylglycerols by reversed phase high performance liquid chromatography with direct liquid inlet mass spectrometry. Can. J. Biochem. Cell Biol, 61, 840-59. 

Another type of ion is formed almost uniquely by the electrospray inlet/ion source which makes this technique so valuable for examining substances such as proteins that have large relative molecular mass. Measurement of m/z ratios usually gives a direct measure of mass for most mass spectrometry because z = 1 and so m/z = m/1 = m. Values of z greater than one are unusual. However, for electrospray, values of z greater than one (often much greater), are quite coimnonplace. For example, instead of the [M + H]+ ions common in simple Cl, ions in electrospray can be [M + n-H]- where n can be anything from 1 to about 30. 

The mass spectra of mixtures are often too complex to be interpreted unambiguously, thus favouring the separation of the components of mixtures before examination by mass spectrometry. Nevertheless, direct polymer/additive mixture analysis has been reported [22,23], which is greatly aided by tandem MS. Coupling of mass spectrometry and a flowing liquid stream involves vaporisation and solvent stripping before introduction of the solute into an ion source for gas-phase ionisation (Section 1.33.2). Widespread LC-MS interfaces are thermospray (TSP), continuous-flow fast atom bombardment (CF-FAB), electrospray (ESP), etc. Also, supercritical fluids have been linked to mass spectrometry (SFE-MS, SFC-MS). A mass spectrometer may have more than one inlet (total inlet systems). 

For non-volatile sample molecules, other ionisation methods must be used, namely desorption/ionisation (DI) and nebulisation ionisation methods. In DI, the unifying aspect is the rapid addition of energy into a condensed-phase sample, with subsequent generation and release of ions into the mass analyser. In El and Cl, the processes of volatilisation and ionisation are distinct and separable in DI, they are intimately associated. In nebulisation ionisation, such as ESP or TSP, an aerosol spray is used at some stage to separate sample molecules and/or ions from the solvent liquid that carries them into the source of the mass spectrometer. Less volatile but thermally stable compounds can be thermally vaporised in the direct inlet probe (DIP) situated close to the ionising molecular beam. This DIP is standard equipment on most instruments an El spectrum results. Techniques that extend the utility of mass spectrometry to the least volatile and more labile organic molecules include FD, EHD, surface ionisation (SIMS, FAB) and matrix-assisted laser desorption (MALD) as the last... 

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 ... 

Various methods of analysis exert different thermal stress on a material (Table 6.39). Direct heating in the inlet of a mass spectrometer in order to obtain a mass spectrum of the total pyrolysate is an example of thermochemical analysis. Mass spectrometry has been used quite extensively as a means of obtaining accurate information regarding breakdown products produced upon pyrolysis of polymers. Low residence times allow detection of high masses. 

Regert, M. and C. Rolando (2002), Identification of archeological adhesives using direct inlet electron ionization mass spectrometry, Anal. Chem. 74(5), 965-975. 

M. Regert, C. Rolando, Identification of archaeological adhesives using Direct Inlet Electron Ionization Mass Spectrometry, Analytical Chemistry, 74, 965 975 (2002). 

Quite often a normal electron ionization mass spectrum appears insufficient for reliable analyte identification. In this case additional mass spectral possibilities may be engaged. For example, the absence of the molecular ion peak in the electron ionization spectrum may require recording another type of mass spectrum of this analyte by means of soft ionization (chemical ionization, field ionization). The problem of impurities interfering with the spectra recorded via a direct inlet system may be resolved using GC/MS techniques. The value of high resolution mass spectrometry is obvious as the information on the elemental composition of the molecular and fragment ions is of primary importance. 

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