Mass spectrometer continuous flow

The CO-TPD measurements were performed in a flow reactor, described elsewhere [12]. A quadropole mass spectrometer continuously analysed the gas composition after the monolith... 

Figure 13.7 Setup for mass specirrmietry-based quantitative real-time analysis. The outlet flow of a cwtinuous stirred enzyme membrane reactor (EMR) is continuously analyzed by multiple reaction monitoring in an electrospray ionization triple quadrupole mass spectrometer after flow reduction (SI), dilution (T) and another flow reduction (S2) (S6j. Reprinted by permission from Macmillan Publishers Ltd Nature Chemical Biology [Bujara, M., SchumperU, M., Pellaux, R., Heinemann, M., Panke, S. (2011) Optimization of a Blueprint f

For use in GC-MS systems, attention should be paid to the injection at the necessary high flow rates in connection with the maximum permitted carrier gas loading of the mass spectrometer. As the injection system is always cold, moisture can accumulate from samples or insufficiently purified carrier gas (Figure 2.75). Because of this, the sensitivity of the mass spectrometer could be compromized. The effect is easy to detect because the mass spectrometer continually registers the water background and because the on-column injector can easily be opened at a particular time so that the carrier gas can pass out via the splitter. 

By passing a continuous flow of solvent (admixed with a matrix material) from an LC column to a target area on the end of a probe tip and then bombarding the target with fast atoms or ions, secondary positive or negative ions are ejected from the surface of the liquid. These ions are then extracted into the analyzer of a mass spectrometer for measurement of a mass spectrum. As mixture components emerge from the LC column, their mass spectra are obtained. 

By allowing any solution, but particularly the eluant from a liquid chromatographic column, to flow continuously (dynamically) across a target area under bombardment from fast atoms or ions (FAB or FIB), any eluted components of a mixture are ionized and ejected from the surface. The resulting ions are detected and recorded by a mass spectrometer. The technique is called dynamic FAB or dynamic LSIMS. 

If samples are introduced continuously, then the measurement of isotope ratios can also be continuous as long as sample is flowing into the flame, and several m/z ratios can be examined with almost any kind of mass spectrometer,... 

Most electrical signals flowing between a mass spectrometer and an attached computer are of the analog type viz., the associated voltage varies continuously with time. 

Nonfractionating continuous inlet. An inlet in which gas flows from a gas stream being analyzed to the mass spectrometer ion source without any change in the conditions of flow through the inlet or by the conditions of flow through the ion source. This flow is usually viscous flow, such that the mean free path is very small in comparison with the smallest dimension of a traverse section of the channel. The flow characteristics are determined mainly by collisions between gas molecules, i.e., the viscosity of the gas. The flow can be laminar or turbulent. 

The mobile phase is pumped through the column at a flow rate of, typically, 1 mlmin If we assume an impurity is present at a level of 0.000001%, this is equivalent to such a compound being continually introduced into the mass spectrometer at a rate of ca. 1 ngs ... 

When FAB is utilized for FC-MS, often known as continuous-flow FAB, a matrix material is added to the HPFC eluent, either pre- or post-column, and this mixture continuously flows to the tip of a probe inserted into the source of the mass spectrometer where it is bombarded by the atom beam (Figure 3.3). 

As previously mentioned, the passage of a continuous flow of mobile phase into the mass spectrometer may give rise to a significant amount of background, as can be seen from the TIC trace shown in Figure 3.13(b). A background mass spectrum, obtained after ca. 0.8 min, is shown in Figure 3.14. 

Specific surface areas of the catalysts used were determined by nitrogen adsorption (77.4 K) employing BET method via Sorptomatic 1900 (Carlo-Erba). X-ray difiraction (XRD) patterns of powdered catalysts were carried out on a Siemens D500 (0 / 20) dififactometer with Cu K monochromatic radiation. For the temperature-programmed desorption (TPD) experiments the catalyst (0.3 g) was pre-treated at diflferent temperatures (100-700 °C) under helium flow (5-20 Nml min ) in a micro-catalytic tubular reactor for 3 hours. The treated sample was exposed to methanol vapor (0.01-0.10 kPa) for 2 hours at 260 °C. The system was cooled at room temperature under helium for 30 minutes and then heated at the rate of 4 °C min . Effluents were continuously analyzed using a quadruple mass spectrometer (type QMG420, Balzers AG). 

Several other interface designs were introduced over this period, including continuous flow fast atom bombardment (CFFAB)" and the particle beam interface (PBI)," but it was not until the introduction of the API source that LC/MS applications really came to the forefront for quantitative analysis. Early work by Muck and Henion proved the utility of an atmospheric pressure interface using a tandem quadrupole mass spectrometer. 

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). 

Principles and Characteristics Continuous-flow (or dynamic) FAB/FTB [102] and frit FAB/F1B [103] offer a means of introducing samples in solution into a continuous flow of solvent which terminates at the modified FAB/FIB probe tip, and they extend the applicability of FAB. Samples are injected through a conventional HPLC injection valve, or solutions are simply drawn in by the high vacuum in the ionisation source of the mass spectrometer. These very similar techniques are particularly amenable to coupling with HPLC columns, and ionisation of the sample is unchanged with respect to conventional FAB and FIB/LSIMS. 

The use of IR pulse technique was reported for the first time around the year 2000 in order to study a catalytic reaction by transient mode [126-131], A little amount of reactant can be quickly added on the continuous flow using an injection loop and then introduce a transient perturbation to the system. Figure 4.10 illustrates the experimental system used for transient pulse reaction. It generally consists in (1) the gas flow system with mass flow controllers, (2) the six-ports valve with the injection loop, (3) the in situ IR reactor cell with self-supporting catalyst wafer, (4) the analysis section with a FTIR spectrometer for recording spectra of adsorbed species and (5) a quadruple MS for the gas analysis of reactants and products. 

E. C. Homing, D. I. Carroll, I. Dzidic, K. D. Haegele, M. G. Homing, and R. N. Stillwell. Liquid Chromatograph-Mass Spectrometer-Computer Analytical Systems A Continuous-Flow System Based on Atmospheric Pressure Ionization Mass Spectrometry. J. Chromatogr., A99(1974) 13-21. 

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