Types of Instruments

Another instrument used in physical chemistry research that employs quadnipole mass filters is the guided ion beam mass spectrometer [31]. A schematic diagram of an example of this type of instrument is shown in figure B 1.7.13. A... 

Frequently an analyst must select, from several instruments of different design, the one instrument best suited for a particular analysis. In this section we examine some of the different types of instruments used for molecular absorption spectroscopy, emphasizing their advantages and limitations. Methods of sample introduction are also covered in this section. 

Each of these experimental designs also uses a different type of instrument. To aid in understanding how they control and measure current and potential, these instruments are described as if they were operated manually. To do so the analyst... 

The concentric cylinder viscometer described in Sec. 2.3, as well as numerous other possible instruments, can also be used to measure solution viscosity. The apparatus shown in Fig. 9.6 and its variations are the most widely used for this purpose, however. One limitation of this method is the fact that the velocity gradient is not constant, but varies with r in this type of instrument, as noted in connection with Eq. (9.26). Since we are not considering shear-dependent viscosity in this chapter, we shall ignore this limitation. 

Changing type of instrument in same service leading to an incident. 

The new gas turbines also utilize Low NO eombustors to reduee the NOx emissions, whieh otherwise would be high due to the high firing temperature of about 2300 °F (1260 °C). These low NOx eombustors require eareful ealibration to ensure an even firing temperature in eaeh eombustor. New types of instrumentation sueh as dynamie pressure transdueers have been found to be effeetive in ensuring steady eombustion in eaeh of the eombustors. 

The following types of instruments are used to make pressure measurements ... 

Thermoeouples are the preferred type of instruments beeause of the sim-plieity in basie design and operation. They ean attain a high level of aeeuraey, are suitable for remote reading, and are robust and relatively inexpensive. 

There are three types of instruments that provide STEM imaging and analysis to various degrees the TEM/STEM, in which a TEM instrument is modified to operate in STEM mode the SEM/STEM, which is a SEM instrument with STEM imaging capabilities and dedicated STEM instruments that are built expressly for STEM operation. The STEM modes of TEM/STEM and SEM/STEM instruments provide useful information to supplement the main TEM and SEM modes, but only the dedicated STEM with a field emission electron source can provide the highest resolution and elemental sensitivity. 

Magnetic sector field instruments have mass resolutions up to m/Am = 20000 quad-rupole instruments are limited to a mass resolution of approximately m/Am = 500. For both types of instrument the a mass range extends to 500. 

On the simplest type of instrument (an explosimeter) only one scale is provided, usually with readings from 0 to 100% LEL. However, the detectable changes produced by combustion are too small to be measured accurately in the presence of the low concentrations of contaminants usually encountered in evaluating potential health hazards. For example, the LEL of even the most explosive gas is of the order of 1 %, or 10,000 ppm, which is well in excess of the toxic limit for any gas. Therefore, explosimeters or combustible gas indicators which have only a 0-to-l(X)% LEL explosive scale are not suitable for environmental health testing in the ppm range. More sensitive instruments, including the type used in sampling for environmental health purposes, have a dual scale, in which the second, more... 

While this permits more sensitive and accurate reading of concentrations in the 0-to-10% range, this type of instrument is not sufficiently sensitive to give precise indications of concentrations at the TLV of many toxic gases and vapors. In addition, they lack specificity, do not read directly in TLV units (ppm), and are subject to interferences. All combustible gas and vapor indicators are calibrated by the manufacturer using one specific gas or vapor such as methane, and a calibration curve is provided, in percent LEL, for the calibration gas only. 

Liquid-in-glass thermometers measure the thermal expansion of a liquid, which is placed in a solid container, on a length scale. The mercury thermometer is one example of liquid thermometers. Alcohol is also used with this type of instrument. The temperature range is -80 to a-330 °C depending on the liquid. The quality, stability, and accuracy vary considerably. The advantages are a simple construction and low price. A disadvantage is that they are not compatible for connection to monitoring systems. 

Electrical manometers have developed during the last 30 years. Modern electrical manometers are well suited for ventilation applications, both in the laboratory and in the field. The advantage of this type of instrument is fhat they are sensitive enough to measure small pressure differences with electrical output, enabling monitoring. A convenient feature, especially in the field is that the instrument is hand-held and there is no need for leveling on a bench, as for fluid manometers. The conversion of the pressure difference into an electrical signal can be based on several different phenomena. 

The blocking effect does not apply to the Pitot-static tube alone. Any sensor/instrument immersed into a duct has a similar effect the larger the sensor is, the greater the problem. For other types of instruments an analysis must be made, so as not to block large proportion of the duct cross-section with the meter. A good rule of thumb to avoid corrections is to keep the cross-section of the meter less than 5% of the duct cross-section. 

It is often experimentally convenient to use an analytical method that provides an instrumental signal that is proportional to concentration, rather than providing an absolute concentration, and such methods readily yield the ratio clc°. Solution absorbance, fluorescence intensity, and conductance are examples of this type of instrument response. The requirements are that the reactants and products both give a signal that is directly proportional to their concentrations and that there be an experimentally usable change in the observed property as the reactants are transformed into the products. We take absorption spectroscopy as an example, so that Beer s law is the functional relationship between absorbance and concentration. Let A be the reactant and Z the product. We then require that Ea ez, where e signifies a molar absorptivity. As initial conditions (t = 0) we set Ca = ca and cz = 0. The mass balance relationship Eq. (2-47) relates Ca and cz, where c is the product concentration at infinity time, that is, when the reaction is essentially complete. 

Collecting optics, radiation detectors and some form of indicator are the basic elements of an industrial infrared instrument. The optical system collects radiant energy and focuses it upon a detector, which converts it into an electrical signal. The instrument s electronics amplifies the output signal and process it into a form which can be displayed. There are three general types of instruments that can be used for predictive maintenance infrared thermometers or spot radiometers line scanners and imaging systems. 

This type of infrared instrument provides a single dimensional scan or line of comparative radiation. While this type of instrument provides a somewhat larger field of view, i.e. area of machine surface, it is limited in predictive maintenance applications. 

In both types of instrument the voltage to be measured is balanced against an external applied voltage (usually from batteries within the instrument). At balance, no current flows through the external circuit and thus errors due to contact resistance are eliminated. 

A further type of instrument employs a hand-generated current passed through the current coil of an ohmmeter and then through a current reverser so that an alternating current is delivered to the current electrodes. Thealter-nating current due to alternating potential between the potential electrodes... 

A variation of the Shepard Cane incorporates both electrodes on a single rod. A circuit diagram of this type of instrument is shown in Fig. 10.51. The single rod has a calibration constant, determined by the area of the positive electrode. At balance the resistivity is given by the resistance multiplied by the rod constant. This instrument is portable and simple to operate, but it cannot be recommended when accurate results are required. 

The advantages of this type of instrument are (a) that only one instrument is required for all necessary measurements, and (b) that it is portable and thus particularly suitable for held work. 

With the increasingly lower limits of detection being achieved in various types of instrumental analysis, there is an ever growing demand for reagents of... 

The instrument is equipped with a prism so that the colour of the liquid under examination and that of the standard which has been selected on the disc are brought into juxtaposition, thus making it easier to compare the two. The Nesslerimeter is a similar type of instrument, made in a tall form to accommodate Nessler tubes. 

There are two basic types of instrument used in plasma emission analysis, namely the simultaneous and the sequential multi-element spectrometer. 

Photoelectric-Colorimetric Method. Although the recording spectrophotometer is, for food work at least, a research tool, another instrument, the Hunter multipurpose reflectometer (4), is available and may prove to be applicable to industrial quality control. (The newer Hunter color and color difference meter which eliminates considerable calculation will probably be even more directly applicable. Another make of reflection meter has recently been made available commercially that uses filters similar to those developed by Hunter and can be used to obtain a similar type of data.) This instrument is not a spectrophotometer, for it does not primarily measure the variation of any property of samples with respect to wave length, but certain colorimetric indexes are calculated from separate readings with amber, blue, and green filters, designated A, B, and G, respectively. The most useful indexes in food color work obtainable with this type of instrument have been G, which gives a... 

MS/MS Instrumentation As was noted previously, a variety of instrument types can perform MS/MS experiments, but because of their popularity, we only discuss MS/MS experiments using triple quadrupole instruments. The principles can be applied to other types of instrumentation. 

Tandem quadrupole and magnetic-sector mass spectrometers as well as FT-ICR and ion trap instruments have been employed in MS/MS experiments involving precursor/product/neutral relationships. Fragmentation can be the result of a metastable decomposition or collision-induced dissociation (CID). The purpose of this type of instrumentation is to identify, qualitatively or quantitatively, specific compounds contained in complex mixtures. This method provides high sensitivity and high specificity. The instrumentation commonly applied in GC/MS is discussed under the MS/MS Instrumentation heading, which appears earlier in this chapter. 

Although it is hkely that the majority of those involved in LC-MS and LC-MS-MS will have one of the instruments described above, it is also worthwhile mentioning two other types of instrument that have MS-MS capabilities, with these being instruments containing both a magnetic sector and an electrostatic analyser (see Section 3.3.3 above), and four-sector systems. 

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