TOFMS spectrometer

The mass spectrometer is a mass-flow sensitive device, which means that the signal is proportional to the mass flow dm/dl of the analyte, i.e. the concentration times the flow-rate. It is only now possible to realise the high (theoretically unlimited) mass range and the high-sensitivity multichannel recording capabilities that were anticipated many years ago. Of considerable interest to the problem of polymer/additive deformulation are some of the latest developments in mass spectrometry, namely atmospheric pressure ionisation (API), and the revival of time-of-flight spectrometers (allowing GC-ToFMS, MALDI-ToFMS, etc.). 

In recent years several new instruments have been developed based on different mass-spectrometer principles. Two different categories of ICP-MS instruments are currently commercially available low-resolution instruments (using either QMS, ITMS or ToF-MS) and focusing high-resolution instruments (DFS, FTMS). Selected specifications for these two categories are shown in Table 8.63. Both the quadrupole-based and the double-focusing instruments allow a sequential multielement measurement, whereas ICP-ToFMS allows... 

Fig. 15.21 The experimental setup including the laboratory-scale coffee roaster with a sampling unit and a laser mass spectrometer. The homebuilt mobile device consisted of a Reflectron TOFMS analyser, an effusive beam inlet system and a built-in laser operated at 266 nm (Continuum NcL YAG laser SURELIGHT", 266 nm). (Adapted from [203])...

Our ongoing target is the development of fully automated glycan analysis and structural profiling systems, by combining SweetBlot and such versatile mass spectrometers as MALDI-TOFMS and other analytical methods used in general... 

A possible solution to the above problems would be the triple-dimensional analysis by using GC x GC coupled to TOFMS. Mass spectrometric techniques improve component identification and sensitivity, especially for the limited spectral fragmentation produced by soft ionization methods, such as chemical ionization (Cl) and field ionization (FI). The use of MS to provide a unique identity for overlapping components in the chromatogram makes identification much easier. Thus MS is the most recognized spectroscopic tool for identification of GC X GC-separated components. However, quadru-pole conventional mass spectrometers are unable to reach the resolution levels required for such separations. Only TOFMS possess the necessary speed of spectral acquisition to give more than 50 spectra/sec. This area of recent development is one of the most important and promising methods to improve the analysis of essential oil components. 

The ionized part of the resulting cluster beam can be analyzed by a time of-flight mass spectrometer (TOFMS) which has been built up at 90° with respect to the beam direction. At the end the produced clusters land onto a substrate (generally a silicon single crystalline one) in a 10 mbar vacuum chamber. The substrate holder can be cooled down to 77 K. Several samples have been deposited at temperatures between 77 and 300 K. 

In order to identify the oxygen-carrying species responsible for the enhanced performance, it was decided to sample the converter gas phase by mass spectrometry. Since cesium can form suboxides with amu around 1,500 (CsjjOj) and because quadrupole mass spectrometers suffer from a transmission loss as the amu rises, a time-of flight mass spectrometer (TOFMS) was chosen. 

A JASCO HPLC system including a Develosil ODS-HG 5 column (Nomura Chemicals 4.6x150 mm solvent, 10-100% aqueous MeOH containing 0.1% TFA in 30 min flow rate, 1.0 mL/min temp, 40 °C monitor at 325 nm) was used for HPLC analysis and for the purification of luciferin (1) and etioluciferin (3). A Voyager-DE PRO Mass Spectrometer (PerSeptive Biosystems) was employed for measuring MALDI-TOFMS of the purified 3 or 1. 

For the more volatile (alkali) metals it has been possible since the late 1970s to create a beam of cold, naked clusters of 1 < n < 100, where n is the number of atoms per cluster 348, 349). Metal vapor is produced in an oven and then cooled by expansion. The clusters are separated in a time-of-flight mass spectrometer (TOFMS). Later it became possible to handle less volatile (transition) metals through vaporization by a laser beam 347, 350-352). For the mass analysis the neutral clusters are photoionized by a suitable UV laser. 

A time-of-flight mass spectrometer (TOFMS) is an excellent instrument for these studies. The TOFMS produces approximately 10 spectra per sec. It is difficult to record individual mass spectra at this rate, but several data acquisition schemes see below) have been developed which record a finite number of discrete spectra. These techniques follow changes in peak intensity over millisecond intervals, thus recording the mass spectra of compounds whose residence time in the ion source is short. 

The microchannel plate is a spatially resolved array detector formed of 10 -10 continuous-dynode electron multipliers, each only 10-100 ptm in diameter. This detector is used in focal plane mass spectrometers as a replacement for photograph plate detectors and is used in some TOFMS instruments. 

Instrumentation for Analytical Chemistry gives rise to many abbreviations forming acronyms . These are often more encountered than the terms they abbreviate, and they appear extensively in the text. A reader new to the field may become lost or disoriented in this thicket of initials. To aid the student in reading the text, the Acronym Index below translates these and indicates the chapter and page where they are best defined or characterized. These acronyms are frequently compounded, as in UV/VIS (ultraviolet/ visible) or LC-CI-TOFMS (Interfaced Liquid Chromatograph to Time-of-Flight Mass Spectrometer operating in Chemical Ionization mode). The components of such compounded acronyms are listed individually in the index, but not aU the possible combinations. 

An advantage of OPTPD-TOFMS is detection of desorbed products in their one pass from a sample to a mass-spectrometer detector through the ionization region with no possibility for other particles (desorbed but not detected at once) to return here. A regime of desorption and observation was realized in the installation of a chamber of black type ( black is due to specific conditions allowing to detect practically only particles desorbed from sample in the one-pass regime, that is, other processes do not distort the signal) [25]. 

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