Special Interfaces

There are other LC/MS interfaces that are less commonly used than ESI and APCI, but are often employed by researchers for analysis of nonpolar or neutral compounds, including particle beam and atmospheric pressure photoionization (APPI). 

1 Atmospheric Pressure Photoionization. Photoionization has been used in mass spectrometry to ionize a variety of compounds [3]. The forma- 

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MACCS-II enables direct interface with other database management systems, such as the Relational Database Management System (RDBMS) and Oracle, so that databases which contain text and numeric data for which special interfaces are normally needed can be constmcted. Eor example, an Oracle MACCS-II linked system is currendy being used by the National Institute on Dmg Abuse (113) to develop a database that will allow scientists to determine the molecular stmctures of cocaine and other controlled substances as well as designer dmgs. 

Are there any special interfaces required of the power supply This would be any power-down interrupts, etc., that may be required by any of the product s circuits. 

CO2 reference standard. A special interface, employing the necessary oxidation and reduction reaction chambers and a water separator, was used employed. For standards of 5-nonanone, menthol and (/ )-"y-decalactone, they were able to determine the correct ratios, with relatively little sample preparation. The technical... 

Detection of the effluent in a 2D system is carried out at the end of the second dimension s column. UVand LIF are the most widely used and the simplest methods of detection for CE separations because they are performed on-column. MS detection, unlike UV and LIF, is carried out on the effluent as it exits the CE column. The direct coupling of CE with mass spectrometry has shown great potential in proteomic research (Janini et al., 2004). The method of choice for detection of peptides is MS-electrospray ionization (ESI). However, ESI requires a special interface between the CE column and the mass spectrometer that has proven not to be a simple matter (Issaq et al., 2004). 

The plasma is maintained at a temperature of 10 000° C by an external radio frequency current, as described in Section 3.3. At this temperature, many molecular species are broken down, and approximately 50% of the atoms are ionized. So far this is identical to ICP-OES, but for ICP-MS we are not interested in the emission of electromagnetic radiation, but rather in the creation of positive ions. To transfer a representative sample of this plasma ion population to the mass spectrometer, there is a special interface between the plasma and the mass spectrometer. This consists of two sequential cones... 

In either case, there is a need to eliminate significant amounts of gas or liquid as the sample passes into the high-vacuum environment of the mass spectrometer. Thus a special interface is needed to accomplish this. But, indeed, reliable interfaces have been invented as evidenced by the extensive use of these techniques in modern analytical laboratories. See Figure 10.21. Also, see additional discussions in Chapters 12 and 13 (Sections 12.6.7 and 13.6.6), as well as Workplace Scene 13.5. 

For the Z-cell, a special interface is constructed for the detection to take place in the length of the capillary instead of the diameter. Two different lengths of capillary with tapered ends on one side are connected with the interface. This takes some experience, so it is important to test putting the set together by different analysts, both experienced and inexperienced. The device is only useful if you have sufficient separation between the analytes of interest, since a longer plug is in the detection window. Consequently, if the analyte bands are simultaneously in the detection window, resolution is no longer observed. A sensitivity enhancement of a factor 10 is possible. 

In order to satisfy the spedflcation outlined above, a special interface was developed. TTie detailed design of this interface, the transport system, and over-pressure system have been the subject of a previous pubhcation and a patent application [24]. The system devised for the interface is based on modifications to an injection system presented by Heilbronner et al. [2S] for preparative gas chromatography. A commercial version of the preparative unit was developed by Boer [26]. In this appfication. samples are monitored into the injection vessel which is connected to the gas chromatographic column by a length of stainless steel capillary tubing. 

MACCS-II enables direct interface with other database management systems, such as Ihe Relational Database Management System RDBMS) and Oracle, so that databases that contain text and numeric data, for which special interfaces arc normally needed, can be constructed. 

Authenticity evaluation has recently received increased attention in a number of industries. The complex mixtures involved often require very high resolution analyses and, in the case of determining the authenticity of natural products, very accurate determination of enantiomeric purity. Juchelka et al. have described a method for the authenticity determination of natural products which uses a combination of enantioselective multidimensional gas chromatography with isotope ratio mass spectrometry (28). In isotope ratio mass spectrometry, combustion analysis is combined with mass spectrometry, and the 13C/12C ratio of the analyte is measured versus a C02 reference standard. A special interface, employing the necessary oxidation and reduction reaction chambers and a water separator, was used employed. For standards of 5-nonanone, menthol and (R)-y-decalactone, they were able to determine the correct 12C/13C ratios, with relatively little sample preparation. The technical details of multidimensional GC-isotope ratio MS have been described fully by Nitz et al. (29). A MDGC-IRMS separation of a natural ds-3-hexen-l-ol fraction is... 

The theoretical basics of LC-NMR coupling have already been discussed in the previous chapter. Except for one type of experiment, the connection of the chromatographic system and the NMR detection cell via a capillary is not sufficient. Most of the experiments require a special interface with switching valves under software control for reliable and reproducible results. The level of equipment and the application field depends on the types of experiment which are being conducted and will be discussed in the following. 

Mass spectrometer can be used as a detector in HPLC analysis. A special interface between the column and the ion source removes the mobile phase solvent and vaporizes the nonvolatile analytes without destroying or rearranging them. The molecules are ionized, and the ions are directed into a quadrupole mass analyzer or into a magnetic sector spectrometer. 

An ideal interface should not cause extra-column peak broadening. Historical interfaces include the moving belt and the thermospray. Common interfaces are electrospray ionization (ESI) and atmospheric pressure chemical ionization (APCl). Several special interfaces include the particle beam—a pioneering technique that is still used because it is the only one that can provide electron ionization mass spectra. Others are continuous fiow fast atom bombardment (CF-FAB), atmospheric pressure photon ionization (APPI), and matrix-assisted laser desorption ionization (M ALDl). The two most common interfaces, ESI and APCI, were discovered in the late 1980s and involve an atmospheric pressure ionization (API) step. Both are soft ionization techniques that cause little or no fragmentation hence a fingerprint for qualitative identification is usually not apparent. 

Iomega s Zip and Jaz drives are detachable, external hard disks that are used to store a large volume (around 100MB for the Zip, 1 and 2GB for the Jaz) of data on a single, floppy-sized disk. The drives connect to either a parallel port or a special interface card. The major use of Zip and Jaz drives is for transporting large amounts of data from place to place. This used to be accomplished with several floppies. 

Some of the newer printers (primarily laser and LED printers) have a special interface that allows them to be hooked directly to a network. These printers have a network interface card (NIC) and ROM-based software that allow them to communicate with networks, servers, and workstations. 

As an alternative to thermal desorption, analytes can be desorbed from the fibre by using organic solvents at a special interface and subsequently analysed by HPLC [222]. 

Direct, on-line coupling of an NMR spectrometer to an HPLC has required the development of special interfaces called flow probes. These systems can basically work in two ways. One is through an on-flow mode (the solute passes through the system as it passes out of the column and is analyzed), but this process has a low sensitivity even when the HPLC column is overloaded. In another way, which is much more used nowadays, the HPLC control unit is equipped with a valve that invokes a stop flow of the effluent when a compound (detected by a UV detector that is always used in connection with these systems) leaves the column in this case, the flow is stopped in order to have enough time for the acquisition of the NMR spectrum. 

Melted snow and ice samples are nebulised at atmospheric pressure and transported into the plasma by an Ar flow. Ions formed in the high temperature plasma are extracted by a special interface with two concentric cones which allow ions to be accelerated and separated by a mass spectrometric analyser and finally detected by a secondary electron multiplier. 

A counter for measuring changes of the resonance frequency can be a common device widely used in electronics. The resolution of frequency should be at least 1Hz within Is interval, the upper limit of frequency should be near 50 MHz. An important feature is the possibility to connect to a personal computer to allow on-line monitoring of the affinity interaction the easiest way is through the standard serial (RS 232C) and USB ports, the GPIB option will require a special interface... 

One of the biggest problems in the early development of GC-MS was interfacing the column outlet to the mass spectrometer. Packed columns were used, and the high volumes of both sample and carrier gas overwhelmed the MS system, which operates under low pressure, and special interfaces had to be built. The advent of fused silica capillary columns meant that the GC-MS interface could be dispensed with, and the column eluent is introduced directly into the ion source. It is essential that column bleeding be minimized since the mass spectrometer will detect the stationary-phase materials. Bleeding is prevented by chemically bonding alkylsiloxanes to the column wall. Other low bleeding stationary phases are mentioned above. 

The equipment consists of two identical rectangular magnetrons mounted side by side in the sputtering chamber. The two magnetrons are connected with a midfrequency power supply of some ten kHz by a special interface. At any time, one of... 

A new technique that resembles the GC-MS technique described here is high-performance liquid chromatography-mass spectrometry (HPLC-MS). An HPLC instrument is coupled through a special interface to a mass spectrometer. The substances that elute from the HPLC column are detected by the mass spectrometer, and their mass spectra can be displayed, analyzed, and compared with standard spectra found in the computer library built into the instrument. 

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