Instrument mechanical interface

In addition to these instruments, an interface was required. The interface serves to count the pulses coming from the autoburet. The time it takes to deliver a preset number of microliters (1,2,5,10...) is measured accurately selection of a higher number of microliters eliminates the effect of mechanical imperfections in the operation of the buret and gives less fluctuating measurements, but also less frequent ones. By the time a CMT measurement has been completed, there is a recording of pH and also of the potential of the corroding metal vs. a separate reference... 

Automatic specimen introduction requires the development of mechanical interfaces between each laboratory analyzer and devices such as conveyor belts, mobile robots, or robot arms. Enhancements to electronic interfaces for laboratory instruments are necessary to allow remote computer control of front-panel functions, notification of instrument status information, and coordination of the distribution of specimens between instruments. Most existing LIS interfaces with laboratory analyzers provide only the ability to download accession numbers and the tests requested on each specimen, and to upload the results generated by the analyzer. 

Although this is standard installation practice for instrumentation the installation stage always presents opportunities for the various parties to get it wrong. One reason for this is the interface between instrumentation, mechanical and electrical teams. 

Instrumental Interfaces. The basic objective for any coupling between a gas chromatograph (gc) and a mass spectrometer (ms) is to reduce the atmospheric operating pressure of the gc effluent to the operating pressure in the ms which is about 10 kPa (10 torr). Essential interface features include the capability to transmit the maximum amount of sample from the gc without losses from condensation or active sites promoting decomposition no restrictions or compromises placed on either the ms or the gc with regard to resolution of the components and reliability. The interface should also be mechanically simple and as low in cost as possible. 

For a decanter that operates under gravity flow with no instrumentation flow control, tire height of the heavy phase liquid leg above the interface is balanced against the height of one light phase above the interface [23]. Figures 4-12 and 4-13 illustrate the density relationships and the key mechanical details of one style of decanter. 

The methods dependent upon measurement of an electrical property, and those based upon determination of the extent to which radiation is absorbed or upon assessment of the intensity of emitted radiation, all require the use of a suitable instrument, e.g. polarograph, spectrophotometer, etc., and in consequence such methods are referred to as instrumental methods . Instrumental methods are usually much faster than purely chemical procedures, they are normally applicable at concentrations far too small to be amenable to determination by classical methods, and they find wide application in industry. In most cases a microcomputer can be interfaced to the instrument so that absorption curves, polarograms, titration curves, etc., can be plotted automatically, and in fact, by the incorporation of appropriate servo-mechanisms, the whole analytical process may, in suitable cases, be completely automated. 

Fortunately, in favorable cases enhancement mechanisms operate which increase the signal from the interface by a factor of 105 — 106, so that spectra of good quality can be observed - hence the name surface-enhanced Raman spectroscopy (SERS). However, these mechanisms seem to operate only on metals with broad free-electron-like bands, in particular on the sp metals copper, silver and gold. Furthermore, the electrodes must be roughened on a microscopic scale. These conditions severely limit the applicability of Raman spectroscopy to electrochemical interfaces. Nevertheless, SERS is a fascinating phenomenon, and though not universally applicable, it can yield valuable information on many interesting systems, and its usefulness is expected to increase as instrumentation and preparation techniques improve. 

The MC-ICP-MS consists of four main parts 1) a sample introduction system that inlets the sample into the instrument as either a liquid (most common), gas, or solid (e.g., laser ablation), 2) an inductively coupled Ar plasma in which the sample is evaporated, vaporized, atomized, and ionized, 3) an ion transfer mechanism (the mass spectrometer interface) that separates the atmospheric pressure of the plasma from the vacuum of the analyzer, and 4) a mass analyzer that deals with the ion kinetic energy spread and produces a mass spectrum with flat topped peaks suitable for isotope ratio measurements. 

To optimize the applicability of the electrothermal vaporization technique, the most critical requirement is the design of the sample transport mechanism. The sample must be fully vaporized without any decomposition, after desolvation and matrix degradation, and transferred into the plasma. Condensation on the vessel walls or tubing must be avoided and the flow must be slow enough for elements to be atomized efficiently in the plasma itself. A commercial electrothermal vaporizer should provide flexibility and allow the necessary sample pretreatment to introduce a clean sample into the plasma. Several commercial systems are now available, primarily for the newer technique of inductively coupled plasma mass spectroscopy. These are often extremely expensive, so home built or cheaper systems may initially seem attractive. However, the cost of any software and hardware interfacing to couple to the existing instrument should not be underestimated. 

Although these experiments did not provide the desired systems needed to amplify chirality, they were helpful in elucidating the stereochemical mechanism of the role played by additives in the early stages of crystal nucleation. This information was instrumental to the elaboration of appropriate model systems for the amplification of chirality, such as the generation of homochiral lysine via crystals of nickel/caprolactam [131] and the auto catalytic process of the spontaneous segregation of racemic enantiomers of amino acids in aqueous solutions assisted by centrosymmetric glycine crystals grown at interfaces. 

The Physical Methods of Chemistiy is a multivolume series that includes Components of Scientific Instruments (Vol. I), Electrochemical Methods (Vol. II), Determination of Chemical Composition and Molecular Structure (Vol. Ill), Microscopy (Vol. IV), Determination of Structural Features of Crystalline and Amphorous Solids (Vol. V), Determination of Thermodynamic Properties (Vol. VI), Determination of Elastic and Mechanical Properties (Vol. VII), Determination of Electronic and Optical Properties (Vol. VIII), Investigations of Surfaces and Interfaces (Vol. IX), and Supplement and Cumulative Index (Vol. X). 

Instrumented tablet presses with computer interfaces allow the pharmaceutical scientist to study the mechanism of compaction and the relationship of the mechanism to tablet-compaction properties and formulations. In addition, automated systems are useful to develop compression profiles for reference purposes, to control weight of tablets during development and production, and to monitor punch wear. This automation reduces the burden on personnel faced with the requirements of quality control. Merck Sharp and Dohme s major production facility in the United Kingdom is fully computerized to manufacture a high-volume tablet product as well as multiple-tablet products. " ... 

Liquid chromatography-mass spectrometiy (LC-MS) based on atmospheric-pressure ionization (API) was demonstrated as early as 1974 (Ch. 3.2.1). However, it took until the late 1980 s before API was starting to be widely applied. Today, it can be considered by far the most important interfacing strategy in LC-MS. More than 99% of the LC-MS performed today is based on API interfacing. In this chapter, instrumentation for API interfacing is discussed. First, vacuum system for MS and LC-MS are briefly discussed. Subsequently, attention is paid to instrumental and practical aspects of electrospray ionization (ESI), atmospheric-pressure chemical ionization (APCI), and other interfacing approaches based on API. The emphasis in the discussion is on commercially available systems and modifications thereof. Ionization phenomena and mechanisms are dealt with in a separate chapter (Ch. 6). Laser-based ionization for LC-MS is briefly reviewed (Ch. 5.9). 

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