Time mass separation

This is the model equation for the calibration of isotope amount ratios based on the log-linear temporal isotope amount ratio regression. Note that a and b are perfectly correlated (p = +1) if Rtp < 1 (inRup < 0) and perfectly anti-correlated (p = —1) if Rk/i > 1 (InRfe/ > 0). It is important to stress that this calibration method is fundamentally different from the conventional mass bias correction la vs. Since the regression model does not invoke the principle of time-mass separation, it does not need either the discrimination exponent or the equality of the discrimination functions [17]. 

Tap Density. Tapping a mass of loose powder, or more specifically, the appHcation of vibration to the powder mass, separates the powder particles intermittently, and thus overcomes friction. This short-time lowering of friction results in an improved powder packing between particles and in a higher apparent density of the powder mass. Tap density is always higher than apparent density. The amount of increase from apparent to tap density depends mainly on particle size and shape (see Table 4). 

In Laser Ionization Mass Spectrometry (LIMS, also LAMMA, LAMMS, and LIMA), a vacuum-compatible solid sample is irradiated with short pulses ("10 ns) of ultraviolet laser light. The laser pulse vaporizes a microvolume of material, and a fraction of the vaporized species are ionized and accelerated into a time-of-flight mass spectrometer which measures the signal intensity of the mass-separated ions. The instrument acquires a complete mass spectrum, typically covering the range 0— 250 atomic mass units (amu), with each laser pulse. A survey analysis of the material is performed in this way. The relative intensities of the signals can be converted to concentrations with the use of appropriate standards, and quantitative or semi-quantitative analyses are possible with the use of such standards. 

In some respects, the time-of-tlight (ToF) analyser is the simplest of the mass separation devices. This system relies on the fact that if all of the ions produced... 

In LGCA models, time and space are discrete this means that the model system is defined on a lattice and the state of the automaton is only defined at regular points in time with separation St. The distance between nearest-neighbor sites in the lattice is denoted by 5/. At discrete times, particles with mass m are situated at the lattice sites with b possible velocities ch where i e 1, 2,. .., b. The set c can be chosen in many different ways, although they are restricted by the constraint that... 

Time of Flight The principle of time-of-flight mass spectrometry (TOFMS) is very simple and makes use of the energy equation E = mv2/2 where m is mass and v is velocity. As illustrated in Figure 11.1, all ions are accelerated to constant energy E. The ions then enter a drift tube where they travel at velocity v. Because each ion mass m travels at a different velocity, the ions of different mass separate the lighter ones run ahead of the heavier ones. This separation means that each ion mass hits the detector at a different time. Ions of the same... 

The most commonly used mass separators are quadrupoles, ions traps and time-of-flight analyzers, for which the principle of mass separation is discussed below. Additionally, other types such as magnetic sector field or Fourier-trans-form cyclotron-resonance instruments are available. 

In a time-of-flight (TOF) analyzer the time of flight of ions between the ion source and the detector is measured [61]. This requires that the time at which the ions leave the ion source is well-defined. Therefore, ions are either formed by a pulsed ionization method or various kinds of rapid electric field switching. The single discontinuous laser pulses at distinct time points used in MALDI can be ideally combined with time-of-flight mass separation. TOF analyzers thus received increasing interest with the development of MALDI MS. The schematic draw of a linear MALDI-TOF MS is shown in Fig. (9). 

To begin, suppose that there exists a particle, P, whose nontrivial dynamics is on a time seale Xp. (In deseribing the dynamics as nontrivial, we mean that there is an appreeiable ehange in the given particle s non-averaged phase-spaee points.) Suppose further that the solute particle is moving within an environment of solvent partieles whose nontrivial dynamics is on a time scale Xe Xp, where the inequality is a result of mass separation, size separation, or some other meehanism. The motion of P can then be described as Brownian motion in whieh P is in some effeetive (averaged) uniform environment. 

Fig. 15.14 Analytical techniques for time-resolved headspace analysis. An electronic nose can be used as a low-cost process-monitoring device, where chemical information is not mandatory. Electron impact ionisation mass spectrometry (EI-MS) adds sensitivity, speed and some chemical information. Yet, owing to the hard ionisation mode, most chemical information is lost. Proton-transfer-reaction MS (PTR-MS) is a sensitive one-dimensional method, which provides characteristic headspace profiles (detailed fingerprints) and chemical information. Finally, resonance-enhanced multiphoton ionisation (REMPI) TOFMS combines selective ionisation and mass separation and hence represents a two-dimensional method. (Adapted from [190])...

Fig. 3.19 Mass separated energy distributions of pulsed-laser field desorbed 4He+ and ions obtained with the Penn State pulsed-laser ToF atom-probe when the flight path length was 778 cm. Their onset flight times are separated by 34 ns, exactly that calculated from the system constants and their critical ion energy deficits at 5.5 kV.

Fig. 8.1.1 Simple illustrations of a various mass spectrometers, a The triple-quadrupole tandem mass spectrometer (top panel). The middle set of quadrupoles are part of the collision cell (CC) and do not perform mass separation. MSI and MS2 indicate the first and second quadrupole mass separation devices, respectively. The bold arrow shows the path of ions, b Ion-trap mass spectrometer (middle left). The charged sections of the ion trap are not elliptical as drawn, but rather hyperbolic. The diagram is also two-dimensional, whereas the ion trap is three-dimensional. The ion path is such that ions enter the device and are trapped until a specific voltage ejects these ions, c Time of Flight mass spectrometer with a Reflectron (middle left). Ions are separated by the time it takes to pass through the instrument. The Reflectron improves/focuses the ions, d Hybrid Tandem mass spectrometer (bottom). The diagram shows that a quadrupole instrument can be combined with a different type of mass spectrometer, forming a tandem hybrid instrument...

Finally, it is important to note there are many other instruments and configurations that are often referred to as tandem mass spectrometers. There are hybrid instruments that use another form of mass separation, time-of-flight (TOF) mass spectrometry. TOF mass spectrometry separates ions based on the time it takes to... 

This fundamental equation explains that the velocity of heavier ions (iq of ions with mass m,) is lower than of lighter ions (v2 of ions with mass m2, with m, > m2). Equation (10) is used directly in time resolved measurements, for example in time-of-flight mass spectrometers (ToF-MS). The charged ions of the extracted and accelerated ion beam are separated by their mass-to-charge ratio, m/z, in the mass analyzer. Mass-separated ion beams are subsequently recorded by an ion detection system either as a function of time or simultaneously. Mass spectrometers are utilized for the determination of absolute masses of isotopes, atomic weights, relative abundance of isotopes and for quite different applications in survey, trace, ultratrace and surface analysis as discussed in Chapters 8 and 9. 

Another type of dynamic mass spectrometer is the time-of-flight (ToF) analyzer. In 1946, Stephens presented his concept of the linear time-of-flight mass spectrometer (ToF-MS) as the simplest mass separation technique at an American Physical Society meeting in Cambridge, MA.49 Cameron and Eggers first published the design and showed mass spectra for linear ToF-MS in... 

Dynamic mass separation systems use the fact that ions with different masses (accelerated with the same voltage) possess several velocities and consequently their flight times are different. There are about 50 dynamic separation systems known2 using several types of ion movements (linear straight ahead, linear periodic or circular periodic as a function of the electric or magnetic sector field applied). The simplest dynamic mass separation system is a linear time-of-flight (ToF) mass analyzer, and a widely applied mass separation system is the quadrupole analyzer. 

Long-lived radionuclides occur at extremely low concentrations, especially in environmental samples, therefore several authors have proposed matrix separation and enrichment of the analytes before analysis.21,24,26,3 39 Radiochemical methods often require very careful and time consuming separation and enrichment processes and measurement procedures of a-, (3- and -emitting radioactive species at the trace and ultratrace level using conventional radioanalytical techniques 40-43 Trace/matrix separation, which is performed offline or online in order to avoid possible isobaric interferences, matrix effects and to reduce the detection limits for the determination of long-lived radionuclides, is also advantageous before ICP-MS measurements as the most widely applied mass spectrometric technique. 

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