On-line analytical instrumentation

Development of reliable flow measurement and on-line analytical instrumentation. 

On-line analytical instruments must be capable of quantitatively measuring gas-phase sulfur concentrations as low as 5 ppb and of quantitatively measuring reactants and products for the reaction under study for a broad range of concentrations. In essentially no previous studies have all these requirements been met (in most cases none of them has). 

Specify type and frequency of analyses (routine or specialized analysis, are on-line analytical instruments necessary ). 

A product gas sample is collected throughout the duration of a run and this composite is analyzed by a mass spectrometer. In addition, a number of on-line analytical instruments have been provided for monitoring unit performance and product gas composition, A Beckman Model A-3 density instrument continuously records the product gas density which, together with the gas measurement and liquid hydrocarbon weight, enables a material balance to be developed within minutes after a run is terminated. Since density (composition) of the product gas is very sensitive to operating conditions, it is invaluable in relating the performance of the reactor and the steadiness of a run,... 

Many other areas of analytical instrumentation have benefited greatly from computerization, and the reader is referred to review articles describing various applications in detail [1]. The objective of this chapter is to introduce the fundamental principles of on-line computer instrumentation, focusing attention on the characteristics of digital devices important for interfacing laboratory instruments to digital computers. These fundamentals include a consideration of number systems. 

I. Landa, Advances in On-line NIR Instrumentation, Eastern Analytical Symp., October 1986, New York. 

Finally it should be mentioned that multipoint ambient air monitors and multicomponent analysis systems are appearing on the analytical instrumentation market. Such systems mostly are based on Fourier transform infrared (FT-IR) spectroscopy or are on-line systems with mass spectrometers. Although such systems enable up to 20 components to be analysed simultaneously, their usefulness for plant surveillance is questionable because of the cost of establishing numerous sampling points around toxic agent disposal facilities. 

Figure 2.12 Schematic representation of an on-line SPE-GC system consisting of three switching valves (VI-V3), two pumps (a solvent-delivery unit (SDU) pump and a syringe pump) and a GC system equipped with a solvent-vapour exit (SVE), an MS instrument detector, a retention gap, a retaining precolumn and an analytical column. Reprinted from Journal of Chromatography, AIIS, A. J. H. Eouter et al, Analysis of microcontaminants in aqueous samples hy fully automated on-line solid-phase extraction-gas chromatography-mass selective detection , pp. 67-83, copyright 1996, with permission from Elsevier Science.

Although SFE and SFC share several common features, including the use of a superaitical fluid as the solvent and similar instrumentation, their goals are quite distinct. While SFE is used mainly for the sample preparation step (extraction), SFC is employed to isolate (chr-omatography) individual compounds present in complex samples (11 -15). Both techniques can be used in two different approaches off-line, in which the analytes and the solvent are either vented after analysis (SFC) or collected (SFE), or on-line coupled with a second technique, thus providing a multidimensional approach. Off-line methods are slow and susceptible to solute losses and contamination the on-line coupled system makes possible a deaease in the detection limits, with an improvement in quantification, while the use of valves for automation results in faster and more reproducible analyses (16). The off-line... 

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