Rapid Data Acquisition

Another benefit of the fast acquisition time is that qualitative or semiquantita-tive analysis is relatively seamless compared to scanning quadrupole technology, because every multielement scan contains data for every mass. This also makes spectral identification much easier by comparing the spectral fingerprint of unknown samples against a known reference standard. This is particularly useful for forensic work, where the evidence is often an extremely small sample. 

There is no question that TOF ICP-MS, with its rapid, simultaneous mode of measurement, excels at multielement applications that generate fast transient signals. 

Practical Guide to ICP-MS A Tutorial for Beginners, Second Edition 

12th Asilomar Conference on Mass Spectrometry, Pacific Grove, CA, September 20-24, 1996. 

Vanhaecke, L. Moens, R. Dams, L. Allen, and S. Georgitis, Analytical Chemistry, 71, 3297, 1999. 

There are a small number of elements that are recognized as having poor detection limits by ICP-MS. These are predominantly elements that suffer from major spectral interferences generated by ions derived from the plasma gas, the matrix components, or the solvent/acid used in sample preparation. Examples of these interferences include the following  

The cold/cool plasma approach, which uses a lower temperature to reduce the formation of the argon-based interferences, has been a very effective way to get around some of these problems. However, this approach can sometimes be difficult to optimize, is only suitable for a few of the interferences, is susceptible to more severe matrix effects, and it can be time consuming to change back and forth between normal and cool plasma conditions. These limitations and the desire to improve performance have led to the commercialization of collision/reaction cells and collision/reaction interfaces. Designs for collision/reaction cells and collision/ reaction interfaces were based on the early work of Rowan and Houk, who used Xe and CH4 in the late 1980s to reduce the formation of ArO+ and Ar2 species in the determination of Fe and Se with a modified tandem mass spectrometer. This research was investigated further by Koppenaal and coworkers in 1994, who 

FIGURE 10.1 Layout of a typical collision/reaction cell instrument. 

The coUision/reaction interface, which will be discussed later in this chapter, uses a slightly different principle to remove the interfering ions. It does not use a pressurized cell before the mass analyzer, but instead, injects a collision/reaction gas directly into the aperture of the interface skimmer cone. The injection of the collision/reaction into this region of the ion beam produces collisions between the argon gas and the injected gas molecules, and as a result, argon-based polyatomic interferences are destroyed or ranoved before they are extracted into the ion optics. 

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The use of magnetic resonance imaging (MRI) to study flow patterns in reactors as well as to perform spatially resolved spectroscopy is reviewed by Lynn Gladden, Michael Mantle, and Andrew Sederman (University of Cambridge). This method allows even unsteady-state processes to be studied because of the rapid data acquisition pulse sequence methods that can now be used. In addition, MRI can be used to study systems with short nuclear spin relaxation times—e.g., to study coke distribution in catalytic reactors. 

Photodiode detectors have already been cited in this chapter in relation to near-IR fluorescence measurements on singlet oxygen,(8 16 18) in decay-time temperature sensing,(50) in liquid chromatography,(62) the study of proteins labelled with Nile Red,(64) and diode laser spectrometry,(67) Photodiodes are also conveniently packaged for many applications in an array form enabling rapid data acquisition e.g., in spectrophotometry, (35)... 

Note that the number of diffraction peaks decreases with time as the droplet diameter decreases, and the number density of peaks is very nearly proportional to the droplet size. The intensity of the scattered light also decreases with size. The resolution of the photodiode array is not adequate to resolve the fine structure that is seen in Fig. 21, but comparison of the phase functions shown in Fig. 22 with Mie theory indicates that the size can be determined to within 1% without taking into account the fine structure. In this case, however, the results are not very sensitive to refractive index. Some information is lost as the price of rapid data acquisition. 

PDA detectors can be operated at rapid data acquisition rates (up to 40 Hz) and are the most common used. Quadrupole MS systems are capable of supplying sufficient spectra for peak. For reliable component assignment, of course, TOF-MS systems possessing higher scan speed can be used. 

The availability of frequent background-free determinations of left ventricular function will open additional uses for evaluation of the left ventricular ejection fraction and volume indices. Rapid data acquisition at varying levels of exercise, frequent assessment of pharmacologic and physiologic interventions, and simultaneous acquisition of data using more than one radionuclide becomes readily feasible with agents such as Au-195m. 

To decrease uncertainty by l/v 10 requires 10 measurements. Instruments with rapid data acquisition allow us to average many experiments in a short time to increase the accuracy of a result. 

Whilst both are potentially useful, the sensitivity of relaxation time measurements at low temperatures is a distinct advantage. Although this sensitivity is decreased at temperatures above room temperature, the spin-lattice relaxation time is very fast which allows for rapid data acquisition and hence a high signal-to-noise ratio. The temperature dependence of the relaxation time measurements was shown to be independent of magnetic interactions above 20 K. This increases the utility of the system since, as a result, small magnetic impurities in the potassium bromide would not affect the values obtained. Combine this... 

Because of the known thermal instability of carbamates at high temperatures, a method of identifying any volatile species would be desirable. The rapid data acquisition possible with FTIR would enable changes in both concentration and composition to be monitored as a function of time. A 10 cm gas cell was modified to enable the measurement of volatile components from... 

Time resolved analysis is essential for monitoring of chromatographic separations. Rapid data acquisition may now be performed, using ICP-MS instruments equipped with software capable of monitoring signal versus time at several different mlz values. 

The upper limit on D is set by the requirement for multiple data points during the transient response, while the lower limit results from the long times required to approach equilibrium. Thus, thinner films (hundreds of nanometers) are better for probing slower diffusion, while thicker film (micrometers) are better for faster diffusion. An electronics scheme capable of rapid data acquisition [98] would enable larger D values to be quantified based on following the rapid transients. 

Forward optic spectrophotometers are either singlebeam or double-beam spectrophotometers. The singlebeam instruments can be either very simple or expensive depending on the sophistication desired or needed. Simple single-beam instruments have poor stability and excessive drift. These advantages are eliminated in systems equipped with a high-resolution monochromator with adjustable slits, controlled by microprocessors for rapid data acquisition and evaluation of data. 

Although NMR is versatile in characterization of molecules and mixtures, often in industrial applications, it is utilized in combination with chromatographic techniques, such as LC-NMR in process control applications to improve efficiency.Recent improvements in sensitivity, the design of flow cells, and rapid data acquisition make NMR a suitable detection system for HPLC. ... 

Another advantage of AES is the speed of the analysis. Cylindrical mirror analysers possess the ability to examine the complete Auger spectrum in less than a second and rapid data acquisition may be critically important in kinetic studies. This very high-speed analysis is most important in the presence of electron beam induced desorption and damages, which are one of the major drawbacks of AES. 

The major advantage of on-line NMR detection as opposed to off-line detection for liquid chromatography (LC) are improved chromatographic resolution, consistent response, and rapid data acquisition. The disadvantages include poorer sensitivity due to limited measurement time and a flow-rate dependence of the NMR linewidth [Webl]. Following the first stopped flow design in 1978 [Wat 1 ], an on-line system had been developed within a year [Bayl], and the techniques have been improved continuously since then [Webl]. 

In terms of spectrometer hardware, short high-power pulses are required to cover a spectral width of up to a few hundred kHz, and fast digitizing is essential for echo experiments [13, 19]. Since Ti relaxation proceeds efficiently by a quadrupolar mechanism, rapid data acquisition is possible. 

In principle reactions that are induced by a light signal could be in the conventional time range, or rapid, requiring rapid data acquisition. The latter class of reactions became a reality in the history of this research area upon the development of fast... 

Rates of this kind are of relatively little use, as it is impossible to sieve out isothermal sets of rates at constant activity. It would take many experiments at different conditions to make available a sufficient data set to allow the sieving out of isothermal data at constant activity. Such data would, however, allow us to compare sets of isothermal rates at a variety of activities and from this determine the parameters of the deactivation equation. Unfortunately, the number of experiments required for this procedure to be applied presents a serious handicap. The method cannot be made compatible with rapid data acquisition. Fortunately, there is a way out of the dilemma. It is possible to unravel decay properties by other much simpler and less laborious means. The method described below (see also Grenier, (1997)) requires as few as two experiments using the decaying catalyst. 

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