Spectrometric system, components

By coupling GC with MS as the detection system (either ion trap or quadrupole mass spectrometer), structural information can be obtained regarding unknown or unexpected components. Another advantage of using mass spectrometric detection is that it can distinguish analytes tagged with stable isotopes, offering the possibility to use them as... 

HPTLC is a very fast and convenient assay to separate samples components and is often used in Organic Chemistry and in Synthetic approach. Unknown substances, after different display assay, were generally scraped off from the TLC/HPTLC plate, diluted into a tube and transferred into the MS system for structural elucidation and characterization. Now, a TLC-MS interface was developed by CAMAG, which can semi-automatically extract zones of interest and on-line direct them into any brand of a HPLC-MS system. The TLC-MS interface is connected by two fittings to any HPLC instrument coupled with mass spectrometer, without other system configuration adjustments or mass spectrometer modifications. By this way, the unknown substances can be directly extracted from a TLC/HPTLC plate, eluted and resolved by HPLC system and sensitive and selective mass spectrometric signals are obtained within a minute per substance zone [33],... 

If the separation mechanisms are independent, then the probability of component overlapping is quite small components, unresolved in first separation according to one parameter, will probably be separated during the second separation. In the case where the two chromatographic separations are preceded by a solvent extraction step, the latter should be considered as a part of the multidimensional system, yielding a 3D system [1], An additional dimension is also represented by a mass spectrometric detector and hence, even 4D systems are achievable. 

Routine spectrometric analyses currently run in industry may involve mixtures of up to 20 or 30 components. The solution of systems of 20 or 30 simultaneous equations by hand calculations is so tedious an operation, and so subject to human error, that it is impractical to accomplish it on a routine basis. The necessary calculations are, however, a well-defined arithmetic procedure easily adapted to digital calculators. Analog computers can also be used in solving simultaneous equations but are subject to accuracy limitations. 

The mass spectra of the gases evolved from the deuterated SWNT sample heated in vacuum were measured with the MI 1201V mass spectrometer. Gas ionization in the ion source of the spectrometer was produced with a 70-eV electron beam. To obtain the gas phase, the sample was placed in a quartz ampoule of a pyrolyzer that was connected to the injection system of the mass spectrometer through a fine control valve. Then the ampoule was evacuated to a pressure of about 2-x 10-5 Pa in order to remove the surface and weakly bound impurities from the sample. After the evacuation, the ampoule was isolated from the vacuum system and the sample was heated to 550°C in five steps. At each step, the sample was kept at a fixed temperature for 3 h then the fine control valve was open and the mass-spectrometric analysis of the gas collected in the ampoule was performed. After the analysis, the quartz ampoule was again evacuated, the valve was closed, and the sample was heated to the next temperature. The measurements were carried out over the range 1 < m/z < 90, where m is the atomic mass and z is the ion charge. The spectrometer resolution of about 0.08% ensured a reliable determination of the gas-phase components. 

Martens-Lobenhoffer et al. [119] used chiral HPLC-atmospheric pressure photoionization tandem mass-spectrometric method for the enantio-selective quantification of omeprazole and its main metabolites in human serum. The method features solid-phase separation, normal phase chiral HPLC separation, and atmospheric pressure photoionization tandem mass spectrometry. The internal standards serve stable isotope labeled omeprazole and 5-hydroxy omeprazole. The HPLC part consists of Agilent 1100 system comprising a binary pump, an autosampler, a thermo-stated column component, and a diode array UV-VIS detector. The enantioselective chromatographic separation took place on a ReproSil Chiral-CA 5 ym 25 cm x 2 mm column, protected by a security guard system, equipped with a 4 mm x 2-mm silica filter insert. The analytes were detected by a Thermo Scientific TSQ Discovery Max triple quadrupole mass spectrometer, equipped with an APPI ion source with a... 

The Knudsen cell mass spectrometric method is well established and has been described in many reviews, as can be seen in references (6-10). It is an important method for equilibrium vapor studies of high temperature systems for temperatures up to approximately 3000 K. There is no other method presently available that permits the measurement of bond energies of minor molecular vapor components at such high tein)eratures. 

We have developed several new measurement techniques ideally suited to such conditions. The first of these techniques is a High Pressure Sampling Mass Spectrometric method for the spatial and temporal analysis of flames containing inorganic additives (6, 7). The second method, known as Transpiration Mass Spectrometry (TMS) (8), allows for the analysis of bulk heterogeneous systems over a wide range of temperature, pressure and controlled gas composition. In addition, the now classical technique of Knudsen Effusion Mass Spectrometry (KMS) has been modified to allow external control of ambient gases in the reaction cell (9). Supplementary to these methods are the application, in our laboratory, of classical and novel optical spectroscopic methods for in situ measurement of temperature, flow and certain simple species concentration profiles (7). In combination, these measurement tools allow for a detailed fundamental examination of the vaporization and transport mechanisms of coal mineral components in a coal conversion or combustion environment. 

The ultimate in selectivity in HPLC detection is seen with the use of mass-spectrometric detection, and for many applications this could be seen as the ideal detection method. However, more mundane considerations such as size of the instrumentation and limited budgets combine to reduce HPLC-MS to a relatively small number of applications which most effectively exploit its unique properties. When such practical constraints are taken into account, the real detector coimected to the HPLC system usually turns out to be a device that is a compromise, and its performance characteristics need to be taken into account during the development of many analyses just as much as the performance of the column or any other component of the HPLC system. For example, lack of detection selectivity may require extra method development to completely resolve an interfering peak, or lack of sensitivity could force the inclusion of an extraction-concentration step in an analytical method to achieve detectable levels of analyte. 

Of all the systems which have been utilized for the analysis of pesticide residues, combined gas chromatography-mass spectrometry afiFords a particularly useful approach because positive identification of the components of a mixture can be made without prior separation at sensitivities compatible with the limited quantities of residues generally available. From the results of recent studies involving the application of this technique, it has been demonstrated that available residue analytical methods provide efficient isolation and adequate cleanup of extracts of human, animal, and environmental media in most cases to permit gas chromatographic-mass spectrometric analyses with maximum confidence. Additionally, it has been shown that this combined technique will conveniently provide definitive and conclusive confirmation of residue identity as well as characterization of residues and their metabolites of unknown structure. 

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