Instrument Description

The light source (1) is a 2mW vertically polarized helium-neon laser which provides a small-diameter, coherent incident beam of 633 nm wavelength which is folded back on itself via a two-prism system (2). This directs the beam toward three measuring attenuators (3, 4, 5) a calibrating/shutter attenuator (6), a condensing lens (7), the sample compartment (8) and finally, through an optical system, to the detector. 

The condensing lens focuses the incident light to a beam width of about 0.08 mm inside the sample, contained between two highly polished fused silica windows and a Teflon spacer. The volume of the measuring cell is 150/d, but the sample volume participating effectively in the scattering amounts to only about 0.1 1. 

The light scattered at small angles, as determined by a series of five annuli (9), is detected by a highly linear photomultiplier (16). These annuli are located 

The scattered light is then imaged by a relay lens (11) onto the field stops (12), which are contained on a wheel and vary in size from 1.5 to 0.005 mm. Beyond the field stops are two lenses between which are inserted an interference filter (13) centered on 633 nm and with a bandwidth of 4nm to eliminate the fluorescence and an analyzing polarizer (14) which measures both the vertical and horizontal components of the scattered light. Immediately behind the field stops lies a microscope objective (15) which allows observation of the light scattered from the sample solution so that the system can be aligned appropriately. 

The procedure employed is thoroughly described in the instrument instructional manual. Thus, the following sections will deal only with the general operations and key operating parameters. 

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However, an encyclopaedia focusing on instruments, which includes material on chemical instruments and apparatus, was published in 1998. It incorporates 327 entries on a diverse range of historical items.4 Its strengths are its fairly comprehensive coverage and inclusion of more recent and complex instruments. Descriptions of the historical development of each item are necessarily short. Though it does not concentrate particularly on chemistry, there is some useful material to be found in a German volume of 37 essays, including a chapter on a subject rarely treated, industrial reaction vessels.5... 

As evident from Fig. 7, and the previous instrumental description, the LR-FDCD system appears similar in configuration to a conventional phase-modulated spectrofluorometer with the exception of the Babinet-Soleil compensator (BSC). The BSC... 

Quantity or property Method or instrument Description On line ... 

Amott W. P., MoosmuUer H., Rogers C. F., Jin T. F., and Bruch R. (1999) Photoacoustic spectrometer for measuring light absorption by aerosol instrument description. Atmos. Environ. 33, 2845—2852. 

Wohltjen H and Dessey R 1979 Surface acoustic wave probe for chemical analysis I. Introduction and instrument description Anal. Chem. 51 1458-64 Schultz J S, Mansouri S and Goldstein I J 1982 Affinity glucose sensor Diabetes Care 5 245-53... 

Instrument Description Time-resolved and time-averaged incident heat flux data were obtained with a water-cooled, circular foil, heat flux gauge radiometer. A schematic of the instrument is shown in Figure 32.7. This instrument consisted of a... 

CO2 is used widely as a solvent for extraction. The advantages of using supercritical CO2 include its low toxicity, low cost, nonflammability, and ease of disposal. Once the extraction is complete and the pressure returns to atmospheric pressure, the carbon dioxide immediately changes to a gas and escapes from the opened extraction vessel. The pure extracted analytes are left behind. Automated SFE instruments can extract multiple samples at once at temperatures up to 150°C and pressures up to 10,000 psi (psi means pounds per square inch and is not an SI unit 14.70 psi = 1 atm). SFE instrument descriptions and applications from one manufacturer, Isco, Inc., can be found at their website (www.isco.com). The SFE methods have been developed for extraction of analytes from environmental, agriculmral, food and beverage, polymer and pharmaceutical samples, among other matrices. 

The electrochemical cell would need quartz windows. A typical three-electrode system, with WE, CE, and reference electrode, is used. Eor IR work, the source and spectrometer would have to be suitable and the windows of the cell would have to be IR transparent, for example, CaFj. Suitable materials have been discussed for both techniques in Chapters 4 and 5. Commercial systems are available from BioLogic Science Instruments, Claix, Erance (www.bio-Iogic.info), and from ZAHNER-Elektrik GmbH Co., KG, Kronach, Germany (www.zahner.de). Their websites contain pictures and detailed instrument descriptions as well as a number of application notes and technical notes. 

Figure 4.7 Schematic of the time-of-flight aerosol mass spectrometer (TOF-AMS). Aerosol is introduced into the instrument through an aerodynamic lens focusing the particles through a skimmer and an orifice onto the vaporizer. Particle vapor is ionized and the ions are guided into the TOF-MS, which generates mass spectra at 83.3 kHz repetition rate. For particle size measurement the particle beam is chopped with a mechanical chopper and the detection is synchronized with the chopper opening time [178], Aerosol Science Technology A New Time-of-Flight Aerosol Mass Spectrometer (TOF-AMS) - Instrument Description and First Field Deployment. 39 637-658. Copyright 2005. Reston, VA. Reprinted with permission...

R. S. Duran and McKenna, A Torsional Dilatometer for Volume Change Measurements on Deformed Glasses Instrument Description and Measurements on Equilibrated Glasses , J. Rheol. 34, 813-839 (1990). 

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