Scanning mass spectrometer

In the modem scanning mass spectrometer, it is more convenient that ions arrive at a single point for monitoring (collection), so r (or r ) is kept constant. Therefore, B or V must be varied to bring all ions to the same focus viz., one of the relationships in Equation 24.5 must apply ... 

It is seen from Figure 15 that the analysis time ranges from about 10,000 seconds (a little less than 3 hr) to about 30 milliseconds. The latter, high speed separation, is achieved on a column about 2 mm long, 12 microns in diameter, operated at a gas velocity of about 800 cm/second. Such speed of elution for a multicomponent mixture is of the same order as that of a scanning mass spectrometer. 

Yaccato K, Hagemeyer A, Lesik A, Volpe A, Weinberg WH. 2004. High throughput screening of low temperature SCR and SCD de-NOx catalysts in scanning mass spectrometer. Top Catal 30/31 127-132. 

Rapid scanning mass spectrometers providing unit resolution are routinely used as chroaatographic detectors. Ion separation is accomplished using either a magnetic sector, quadrupole filter or ion trap device. Ions can also be separated by time-of-flight or ion cyclotron resonance mass analyzers but these devices are not widely used with chromatograidiic inlets and will not be discussed here [20]. 

In addition to neutral loss scans, mass spectrometers can be used to detect other compounds in a different manner. Acylcamitines are fatty acid esters of carnitine. The masses of acylcamitines differ by the size of the fatty acid attached to it. The tandem mass spectrometer can detect these selectively as well because they all produce a similar product, in this case an ion rather than a molecule. Because it is an ion, it can be detected by the second mass separation device. The ion has a mass of 85 Da and is common to all acylcamitines. Performing a precursor ion scan of 85 Da (essentially a scan of only molecules that produce the 85 ion) reveals a selective analysis of acylcar-nitines, as shown in Fig. 14.2. Additional scans have been added to more selectively detect basic amino acids, free carnitine, short chain acylcamitines and a hormone, thyroxin (T4) which has amino acid components. 

The procedures for irradiation, collection, and analysis of the volatile compounds have all been described (1, 2, 3, 5, 7, 9, 11). A cryogenically programmed gas chromatograph coupled to a rapid scanning mass spectrometer provided for the analysis of the volatile components isolated from several irradiated meats and lipid substances (6). These studies have now been extended to include other component substances in order to acquire still further understanding of the source of the irradiation-induced volatile compounds from among the various meat constituents. 

Mutlib, A., Lam, W., Atherton, J., Chen, H., Galatsis, P., and Stolle, W. (2005). Application of stable isotope labeled glutathione and rapid scanning mass spectrometers in detecting and characterizing reactive metabolites. Rapid Commun. Mass Spectrom. 19 3482-3492. 

Fig. 3.5 (a) Scanning mass spectrometer (b) schematic of scanning probe tip and its operation. 

A catalyst design strategy based on ternary metal oxides with catalytic and chemical constraints limited the desired set of catalyst compositions to about 100000, a number that could be tested in the scanning mass spectrometer [46]. A feed gas mixture of C2H6, 02, and Ar (4 1 5) was created using a set of digital... 

Micro structured wells (2 mm x 2 mm x 0.2 mm) on the catalyst quartz wafer were manufactured by sandblasting with alumina powder through steel masks [7]. Each well was filled with mg catalyst. This 16 x 16 array of micro reactors was supplied with reagents by a micro fabricated gas distribution wafer, which also acted as a pressure restriction. The products were trapped on an absorbent plate by chemical reaction, condensation or absorption. The absorbent array was removed from the reactor and sprayed with dye solution to obtain a color reaction, which was then used for the detection of active catalysts by a CCD camera. Alternatively, the analysis was also carried out with a scanning mass spectrometer. The above-described reactor configuration was used for the primary screening of the oxidative dehydrogenation of ethane to ethylene, the selective oxidation of ethane to acetic acid, and the selective ammonoxidation of propane to acrylonitrile. 

Figure 3.35 Ethylene produced by oxidative dehydrogenation of ethane over Mo-V-Nb and Ni-Ce-Ta oxide catalyst libraries. The detection of ethylene was performed in a scanning mass spectrometer using a photothermal deflection method. Inactive Mo-V-Nb oxide catalyst (a) active Ni-Ce-Ta oxide library (b) [7] (by courtesy of Kluwer Academic Publishers).

To scan the large number of catalysts, a scanning mass spectrometer was used. By applying this analytical technique, measurement, of both the activity and selectivity of more than 100 catalysts in a library within 3 h is possible. 

Figure 3.49 Schematic of experimental set-up fora scanning mass spectrometer-assisted catalyst screening device [80] (by courtesy of AlChE).

Figure 3.50 Intensity of the C02 signal measured by a scanning mass spectrometer. Reaction conditions reaction temperature, 350 °C stochiometric Co and 02 ratio ...

Since a scanning mass spectrometer was used for measuring the conversion, 144 experiments were carried out within 2 h [80],... 

Is the required precision beyond the capabilities of a scanning mass spectrometer If so, then an ICP-MS fitted with a multicollector array will be the minimum requirement. 

Tandem systems can operate in two ways and the method selected depends on the relative speed of sample generation from the chromatograph and the speed at which the sample can be scanned in the spectrometer. If the spectroscopic data can be obtained rapidly, as with a fast scanning mass spectrometer, then the column eluent or a portion thereof, can be fed directly into the spectrometer, assuming certain precautions are taken and the appropriate interface is used. 

Phillips and Schiff used this source of O atoms in conjunction with a rapid scanning mass spectrometer to investigate reaction (48) they found... 

Mass spectroscopic runs were made on a CEC 21-103C spectrometer. GC/ MS runs were made on a DuPont 21-491 system composed of a PE 900 GC and a DuPont 21-491 magnetic scanning mass spectrometer. The samples were run on a 10-ft by 1/8-in. SE 30 column. 

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