Instruments and their use

A. II. Snell (Ed.), Nuclear Instruments and their Uses, Wiley, New York, 1962 G. D. O Kelley, Detection and Measurement of Nuclear Radiation, NAS-NS 3105, Washington, DC, 1962... 

Franzen, W., and Cochran, L. W., Pulse Ionization Chambers and Proportional Counters, in A. H. Snell (ed.). Nuclear Instruments and Their Uses, Wiley, New York, 1962. 

Steinberg, E. P. 1962. Counting methods for the assay of radioactive samples in Nuclear Instruments and Their Uses. Chapter 5. Snell, A. H., ed. New York, NY John Wiley. Stevenson, P. C. and Nervik, W. E. 1961. The Radiochemistry of the Rare Earths Scandium,... 

The present chapter does not pretend to be an exhaustive record of Solid-Liquid calorimetry applications in Surface Science and Technology. It should be rather regarded as an introductory course with some illustrative examples. It is important to realise that the individual author s experience in the field has been the principal criterion for selection of specific instruments and their uses, without any intention of neglecting other contributions. The presentation of calorimetry methods will be restricted only to interfacial systems composed of a pure liquid or a dilute binary, at the most, solution in contact with a solid which does not dissolve in the liquid phase. This formalism may be still employed in the case of solutions which are not strictly binary but may be viewed as such (e.g., solutions containing ionizable solutes, background electrolytes or other additives that may be lumped together as constituting a mean solvent or a mean solute). 

The apparatus required for classical procedures is cheap and readily available in all laboratories, but many instruments are expensive and their use will only be justified if numerous samples have to be analysed, or when dealing with the determination of substances present in minute quantities (trace, subtrace or ultratrace analysis). 

The two-pulse TR experiments allow one to readily follow the dynamics and structural changes occurring during a photo-initiated reaction. The spectra obtained in these experiments contain a great deal of information that can be used to clearly identify reactive intermediates and elucidate their structure, properties and chemical reactivity. We shall next describe the typical instrumentation and methods used to obtain TR spectra from the picosecond to the millisecond time-scales. We then subsequently provide a brief introduction on the interpretation of the TR spectra and describe some applications for using TR spectroscopy to study selected types of chemical reactions. 

Sections on matrix algebra, analytic geometry, experimental design, instrument and system calibration, noise, derivatives and their use in data analysis, linearity and nonlinearity are described. Collaborative laboratory studies, using ANOVA, testing for systematic error, ranking tests for collaborative studies, and efficient comparison of two analytical methods are included. Discussion on topics such as the limitations in analytical accuracy and brief introductions to the statistics of spectral searches and the chemometrics of imaging spectroscopy are included. 

This chapter covers briefly the environmental factors which contribute to the reliability of results, including laboratory design, siting of instruments and their maintenance. Mistakes often happen because simple actions are omitted, e.g. containers are not correctly or adequately labelled, incorrect containers are used or instructions are ambiguous. 

In addition, Lavoisier and his colleagues introduced programmatically into the chemical laboratory apparatus other than the furnace, the crucible, and the retort, describing and illustrating the new instruments construction and their use in texts like Lavoisier s Traite elementaire de chimie. Lavoisier employed not only the balance and the thermometer but pneumatic apparatus, the electrical machine, the burning lens, and the calorimeter. 80 As the instruments of the chemical laboratory proliferated, so, too, did the problems chemists dreamed of posing and resolving. 

Beyond perfonnance optimization, issues relative to packaging and the need for compliance with certain safety and electronics regulatory codes are cited as reasons for a customized solution. In the latter case, a systems approach is required, especially when attempting to meet the code or performance requirements for compliance with European Certification (CE) mark or electrical and fire safety codes such as National Eire Prevention Association (NFPA) and CENELEC (European Committee for Electrotechiucal Standardization). Off-the-shelf electronics may provide the necessary performance characteristics for generic applications, and their use eliminates large expenses related to product development, plus the associated time delays. Photonics-related components are solely addressed in this section because they are used to customize instruments for application-specific systems. 

Sweeney RE, Kaplan IR (1980) Natural abundance of as a source indicator for near-shore marine sedimentary and dissolved nitrogen. Mar Chem 9 81-94 Sweeney RE, Liu KK, Kaplan IR (1978) Oceanic nitrogen isotopes and their use in determining the source of sedimentary nitrogen. In Robinson BW (ed.) DSIR Bull 220 9-26 Swihart GH (1996) Instrumental techniques for boron isotope analysis. Rev Miner 33 845-862 Swihart GH, Moore PB (1989) A reconnaissance of the boron isotopic composition of tourmaline. Geochim Cosmochim Acta 53 911-916... 

Microcalorimetry has gained importance as one of the most reliable method for the study of gas-solid interactions due to the development of commercial instrumentation able to measure small heat quantities and also the adsorbed amounts. There are basically three types of calorimeters sensitive enough (i.e., microcalorimeters) to measure differential heats of adsorption of simple gas molecules on powdered solids isoperibol calorimeters [131,132], constant temperature calorimeters [133], and heat-flow calorimeters [134,135]. During the early days of adsorption calorimetry, the most widely used calorimeters were of the isoperibol type [136-138] and their use in heterogeneous catalysis has been discussed in [134]. Many of these calorimeters consist of an inner vessel that is imperfectly insulated from its surroundings, the latter usually maintained at a constant temperature. These calorimeters usually do not have high resolution or accuracy. 

The aim is to make a measurement as close to the selected temperature as possible, so speed is essential to minimize temperature changes. Several instruments are fitted with a microswitch to begin the recording regimen as soon as a sample tube is in place, and their use is recommended. 

Hand-held portable XRFs, such as the one used for analyzing our coins, have improved considerably over the last few years. The quality of the instruments and their accuracy has increased and has become quite reliable. The development and commercialization of small XRF devices was, until recently, limited by the poor energy resolution of the detectors and by problems associated with transportation of radioisotopic X-ray sources (5,6). These shortcomings have now been overcome due to the development of thermo-electrically cooled detectors with improved energy resolution and the production of small dedicated X-ray tubes with good stability (7). This offers the ability to analyze elements from Ti(Z=22) to U(Z=92). 

From the experimental standpoint, the use of a.c. techniques offers many advantages. Sensitivity is much higher than in d.c. measurements, since phase-sensitive detection can be used and very small probe signals can be employed ( 5mV). The technique is therefore a truly equilibrium one, unlike cyclic voltammetry. An alternative approach to the commonly used sinusoidal signal superimposed on the selected d.c. potential is to use a potential step and to employ Laplace transform methods. Instrumentally, this is rather more demanding and the advantages are not clear [51]. Fourier transform methods have also been considered and their use will have advantages in terms of the time-scale for an experiment, especially at very low frequencies. 

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