Mass spectrometers interfaceable

The MC-ICP-MS consists of four main parts 1) a sample introduction system that inlets the sample into the instrument as either a liquid (most common), gas, or solid (e.g., laser ablation), 2) an inductively coupled Ar plasma in which the sample is evaporated, vaporized, atomized, and ionized, 3) an ion transfer mechanism (the mass spectrometer interface) that separates the atmospheric pressure of the plasma from the vacuum of the analyzer, and 4) a mass analyzer that deals with the ion kinetic energy spread and produces a mass spectrum with flat topped peaks suitable for isotope ratio measurements. 

The use of existing LC/MS instruments requires that the investigator appreciate certain limitations associated with the linking of separation techniques to the mass spectrometer interface to optimize signal production and to maintain operating efficiency. These limitations are described in the following sections. 

Bemet, P., Blaser, D., Berger, S., and Schaer, M. (2004). Development of a robust capillary electrophoresis-mass spectrometer interface with a floating sheath liquid feed. Chimia (Aarau) 58, 196-199. 

Nanoflow HPLC—HPLC system with accurately controlled reciprocating and syringe pumps designed to use capillary and small diameter, high-resolution columns as front ends for electrospray and nanospray mass spectrometer interfaces. 

Smith, R. D. Johnson, A. L. 1981. Deposition method for moving ribbon liquid chromatograph-mass spectrometer interfaces. Anal Chem., 53, 739-740. 

Mass spectrometers Interface dependent Interface dependent Universal, within limits imposed by interface Complex, expensive devices highly dependent on an efficient interface electrospray and thermospray interfaces are most common linear response is difficult to achieve... 

The low-voltage, high-resolution mass spectra (LVHRMS) were obtained on a Kratos MS-50 high-resolution mass spectrometer interfaced to a Kratos DS-55 data system. The Rasa coal extract was vaporized directly into the ion source by a direct-insertion probe. Spectra were recorded at probe temperatures of 100°C, 200OC, 300°C, and 350°C. The instrument was scanned from 700 to 60 amu at a scan... 

A Hewlett-Packard Model 5970 Mass Spectrometer interfaced with a Hewlett-Packard Model 5890 Gas Chromatograph was used for sample analysis and identification. Chromatographic conditions were the same as above. All mass spectra were obtained at 70 ev El. 

Further chromatographic peak identification also was carried out by interfaced GC-mass spectrometry (MS) using a Hitachi-Perkin Elmer RMU6L mass spectrometer interfaced through a jet separator (Scientific Glass Engineering Pty., Melbourne, Australia). 

The plasma/mass spectrometer interface allows the import of a stream of ions from the plasma, at atmospheric pressure, into the mass spectrometer, which is under vacuum. The interface has a sample cone and a skimmer cone, usually of nickel and typically with 1.0 mm and 0.8 mm apertures, respectively. The turbomolecular pump is presently the most widely used type in the vacuum system. 

Tandem MS. The thermospray HPLC/MS/MS was performed on a Finnigan MAT TSQ-46C triple quadrupole mass spectrometer interfaced to an INCOS Data System (Finnigan MAT, San Jose, CA). The triple quadrupole was operated with the first and second quadrupoles in the RF mode during HPLC/MS operation. For HPLC/MS/MS analysis, the first quadrupole selected the [M+H] ion of the compound, while the third quadrupole was scanned over the mass range of 12-300 daltons. The second quadrupole serves as a collision chamber. Argon collision gas was added to the enclosed chamber of this quadrupole to give a pressure of 2 mtorr for collisional activation of the sample ions. 

ML Vestal, GJ Fergusson. Thermospray liquid chromatograph mass spectrometer interface with direct electrical heating of the capillary. Anal Chem 57 2373-2378, 1985. 

Morgan, D.G. Harbol, K.L. Kitrinos, RN. Optimization of a Supercritical Fluid Chromatograph-Atmospheric Pressure Chemical Ionization Mass Spectrometer Interface Using an Ion Trap and Two Quadrupole Mass Spectrometers, J. Chromatogr. A 800, 39 9 (1998). 

Filtration is used as a sample-preparation method to remove particulates and debris that can potentially foul the LC lines, column frits, or mass spectrometer interface. Also, it is generally accepted that all workstations and pipetting systems can beneht from sample hltration because of the universal issues related to plasma clot formation that introduce pipetting challenges. Applications that use hltration include the removal of a mass of precipitated protein or of debris from raw plasma before use with any of the traditional sample-preparation techniques, as well as direct injection techniques (turbulent how... 

One important aspect which should he pointed out is that there is a basic incompatibihty between GC and MSD, the mass spectrometer operate at pressures of 10- torr or less, whereas the gas chromatograph effluent operates at about 760 torr. An interface device is necessary to handle the pressure differences. The simplest and most efficient interface in GC/MSD is a direct capillary column interface. The low flow rate of the narrow bore column and the high pumping rate of an oil diffusion pump backed by a suitable direct drive mechanical pump assure pressures less than lO " torr and allow for the direct insertion of the colmnn end into the mass spectrometer. Interfacing megabore... 

Figure 11.17 Schematic diagram of the inductively coupled plasma/mass spectrometer interface. From Dean, J. R., Atomic Absorption and Plasma Spectroscopy, ACOL Series, 2nd Edn, Wiley, Chichester, UK, 1997. Reproduced with permission of the University of Greenwich.

Thernospray HPLC/MS. Urine extracts were analyzed by thermospray/HPLC/MS to Identify the metabolites present. A Finnigan 4500 series mass spectrometer Interfaced with a Vestec Thermospray unit was used to perform the analysis. The aerosol thermocouple of the Interface was replaced with a repeller which was connected to an external power supply. The samples were analyzed under thermospray/fllament chemical Ionization with pulsed +/- Ion detection. A mobile phase consisting of acetonitrlle/0.1 M ammonium acetate with a linear gradient of 9X to 65% over 30 minutes was used In the anlaysls. 

The equipment and procedures have been described in detail elsewhere [2-4]. The apparatus consists of a microbalance which is mounted inside a high vacuum chamber that can be evacuated to a background pressure of lO" torr. A quadrupole mass spectrometer, interfaced to a microcomputer, was used to sample the desorbing products. Approximately 15 mg of sample were spread in a thin layer over a flat sample pan in order to minimize bed effects in desorption [7,8]. The TPD-TGA experiments were performed with a heating rate of 10K/min. Isopropylamine was the molecule which was studied in most detail, and all of it was found to desorb completely during the experiment. 

Routine operation of the mass spectrometer interface tip at high temperature might cause the decomposition of thermally-labile materials. Historically, cholesterol has been used to test the thermal activity of GC-MS interfaces and jet separators. It is very sensitive to dehydration across the 3-4 bond upon contact with "active sites" in the system, yielding a species with molecular weight 368 Da (25). 

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