Basic Principle of Operation

A quadrupole operates by placing both a direct current (DC) field and a time-dependent alternating current (AC) of radio frequency on opposite pairs of the fonr rods. By selecting the optimum AC/DC ratio on each pair of rods, ions of a selected mass 

FIGURE 7.3 Schematic representation showing principles of mass separation using a quadrupole mass filter. 

Quadrupole scan rates are typically on the order of 2500 amu per second and can cover the entire mass range of 0-300 amu in about one tenth of a second. However, real-world analysis speeds are much slower than this, and in practice, 25 elements can be determined in duplicate with good precision in 1-2 min, depending on the analytical requirements. 

In this simplihed example, the analyte ion (black) and four other ions (gray) have arrived at the entrance to the four rods of the quadrupole. When a particular AC/DC potential is applied to the rods, the positive or negative bias on the rods will electrostatically steer the analyte ion of interest down the middle of the four rods to the end, where it will emerge and be converted to an electrical pulse by the detector. The other ions of different m/z values will be unstable, pass through the spaces between the rods, and be ejected from the quadrupole. This scanning 

FIGURE 7.2 Photograph of a quadrupole system mounted in its housing. (Courtesy of PerkinElmer, Inc., 2003-2012. All rights reserved. With permission.) 

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The principles of operation of quadnipole mass spectrometers were first described in the late 1950s by Wolfgang Paul who shared the 1989 Nobel Prize in Physics for this development. The equations governing the motion of an ion in a quadnipole field are quite complex and it is not the scope of the present article to provide the reader with a complete treatment. Rather, the basic principles of operation will be described, the reader being referred to several excellent sources for more complete infonnation [13, H and 15]. 

Basic Principles of Operation RO and NF are pressure-driven processes where the solvent is forced through the membrane by pressure, and the undesired coproducts frequently pass through the membrane by diffusion. The major processes are rate processes, and the relative rates of solvent and sohite passage determine the quality of the product. The general consensus is that the solution-diffusion mechanism describes the fundamental mechanism of RO membranes, but a minority disagrees. Fortunately, the equations presented below describe the obseiwed phenomena and predict experimental outcomes regardless of mechanism. 

Basic Principles of Operation Gas-separation hterature often... 

In Section 13.2, we introduce the materials used in OLEDs. The most obvious classification of the organic materials used in OLEDs is small molecule versus polymer. This distinction relates more to the processing methods used than to the basic principles of operation of the final device. Small molecule materials are typically coated by thermal evaporation in vacuum, whereas polymers are usually spin-coated from solution. Vacuum evaporation lends itself to easy coaling of successive layers. With solution processing, one must consider the compatibility of each layer with the solvents used for coating subsequent layers. Increasingly, multilayered polymer devices arc being described in the literature and, naturally, hybrid devices with layers of both polymer and small molecule have been made. 

The pCOj electrode was first described in 1957 by Stow and later improved to its presently used form by Severinghaus The basic principle of operation relies on equilibration of COj with an aqueous solution. The change in pH in the aqueous solution associated with the equilibration due to carbonic acid formation (H2CO3) is measured and varies with log pCO2] It should be pointed out here that these measurements (and likewise for the pO electrode described below) give CO2 tension not concentration. To obtain concentration, Henry s Law of gas solubUity must be applied. However, for most medical and biological applications the knowledge of the gas tension is sufficient. 

Basic Principles of Operation Gas-separation literature often uses nomenclature derived from distillation, a practice that will generally be followed here. L is the molar feed rate, V is the molar permeate rate, R is the molar residue (L — V). Mole fractions of components i, j, in the feed-residue phase will be Xj, Xj. .. and in the permeate phase yi,yj.... Stage cut, 0, is permeate volume/feed volume, or V/L. 

The first SRS unit was built as a demonstration plant and has been in operation since September 1997. The basic principle of operation is that a solution of sodium chloride and sodium sulphate in contact with a nanofiltration membrane at high pressure, will separate into a sulphate-lean permeate stream and a sulphate-rich concentrate stream. 

Under the headline of instmmentation we shall mainly discuss the different types of mass analyzers in order to understand their basic principles of operation, their specific properties and their performance characteristics. Of course, this is only one aspect of instmmentation hence topics such as ion detection and vacuum generation will be addressed in brief. As a matter of fact, sample introduction is more closely related to particular ionization methods than to the type of mass analyzer employed, and therefore, this issue is treated in the corresponding chapters on ionization methods. The order of appearance of the mass analyzers in this chapter neither reflects the ever-changing percentage they are employed in mass spectrometry nor does it strictly follow a time line of their invention. Instead, it is attempted to follow a trail of easiest understanding. 

The scope of the use of mass spectrometry in the protein analysis has grown enormously in the past few decades. MS has become an important analytical tool in biological and biochemical research. Its speed, accuracy and sensitivity are unmatched by conventional analytical techniques. The variety of ionization methods permits the analysis of peptide or protein molecules from below 500 Da to as big as 300 Da (Biemann 1990 Lahm and Langen 2000). Basically, a mass spectrometer is an instrument that produces ions and separates them in the gas phase according to their mass-to-charge ratio (m/z). The basic principle of operation is to introduce sample to volatilization and ionization source, and then the molecular fragments from the ionization of the sample are detected by various kinds of detector and the data are analyzed with computer software. 

Describe the basic principles of operation of low-energy electron diffraction (LEED). 

For all our purposes, a synthetic ion-selective membrane is nothing but a thin sheet of dense nonporous ion-exchanger. In fact, producing a sheet out of a conventional ion-exchanger was exactly the way in which ion-selective membranes were prepared a few decades ago this is the reason why they are still often called ion-exchange membranes. Yet, the basic principles of operation of a bulk ion-exchanger and of an ion-exchange membrane are... 

A typical nozzle-beam system with associated electrospray apparatus is shown schematically in Figure 2. Although nozzle-beam systems differ widely in the details of construction, the basic principles of operation are the same. 

The production of flat-panel cathode ray tubes (CRTs) is essentially a fabrication issue. The basic principle of operation is the same as a standard CRT. Electrons are emitted from a hot cathode. These are guided by a magnetic field to the glass screen coated in a layer of phosphorescent material. Upon impact the energy of the electron is transferred to the phosphor and light is emitted. A regular pattern of red, green and blue phosphors creates a dense pattern of... 

In order to understand the basic principles of operation of the many different kinds of LCDs being developed and/or manufactured at the present time, it is necessary to briefly describe the liquid crystalline state and then define the physical properties of direct relevance to LCDs. First, the nematic, smectic and columnar liquid crystalline states will be described briefly. However, the rest of the monograph dealing with liquid crystals will concentrate on nematic liquid crystals and their physical properties, since the vast majority of LCDs manufactured operate using mixtures of thermotropic, non-amphiphilic rodlike organic compounds in the nematic state. 

The basic principle of operation of gas filled detectors, be it multiwire proportional chambers or linear devices, with a single anode wire, is the mechanism of gas amplification. This kind of detectors have — as its name implies, a filling of an... 

The basic principles of operation which have been explained so far, are valid for one dimensional or linear detectors as well as for two-dimensional gas filled detector systems. 

Hot packs and cold packs are sold in various sports supply stores and pharmacies for the treatment of muscle ache and sports injuries. Although usually made with different salts, the basic principles of operation are the same as the preceding demonstration. 

Basic Principle of Operation of Polymer Electrolyte Membrane Fuel Cells.760... 

Industrial electrolyzers use electrodes and gas collection schemes optimized to produce the maximum amount of hydrogen using the minimum size equipment and minimum quantity of electric energy. Their basic principle of operation is an extension of the simple process described above. Equipment for the industrial scale production of hydrogen by electrolysis is available from a number of manufacturers. Some of these are ... 

In this introductory book chapter, several modem extraction techniques will be described, including supercritical fluid extraction, pressurized liquid extraction, pressurized hot Avater extraction, microwave assisted extraction, membrane-assisted solvent extraction, solid phase micro extraction and stir-bar sorptive extraction. These are techniques that meet many of today s requirements in terms of environmental sustainability, speed and automation. Basic principles of operation as well as method optimization will be discussed and compared for the different techniques. Both analytical and industrial applications will be discussed, together with commercial instruments available on the market. Key references will be given, and conclusions regarding applicability of the different techniques with respect to sample e, target-molecules and analytical vs. large-scale applications. 

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