Infrared plant analyzer

FIGURE 37.1 Infrared plant analyzer from 1943. (Courtesy of J. Appl. Spectrosc.)... 

Infrared gas analyzers have been used to record differential ppm levels of CO2 and water vapor in the study of photosynthetic mechanisms in investigations of plant growth, and COj has been monitored in the effluent air from bacterial cultures. 

Gas exchange measurements. Photosynthetic CO2 gas exchange rate (CER) measurements were made with an ADC infrared gas analyzer. Carbon reduction rates for early (0600-0950 or 1000), midday (1000 or 0950-1700 or 1850 or 1900), late (1700 or 1850 or 1900-2150) and all day were calculated by integrating the CER area over that time period for the 9 plants of each biotype. 

Another important field where PAS has been successfully employed is green plant photosynthesis. Although there are many techniques available to study photosynthesis, not many are applicable to the comprehensive investigation of photosynthesis of intact plants. Even among the techniques that measure the intact leaf photosynthesis, their applications are limited to specific photosynthetic parameters. For example, an infrared gas analyzer can be used only to measure the carbon dioxide uptake during photosynthesis. Similarly, the oxygen electrode technique can... 

The plant is controlled by a process computer (ABB-Hartmann and Braun) and equipped with numerous data-collecting instruments. Surveillance is carried out by continuous analysis of the room air as well as by explosion-limit controls. The pyrolysis gas is analyzed automatically by a gas chromatograph. All data obtained are registered to enable calculation of energy and mass balances. Some basic components are continuously monitored by infrared spectroscopy, i.e. ethylene in the pyrolysis gas, sulphur dioxide and oxygen in the exhaust gas. 

Traditionally, flavonoids have been separated and analyzed by HPLC and gas chromatography (GC). However, recent developments of SFC may permit a more accurate and complete analysis of plant phenolic compounds. Supercritical fluid chromatography brings together the advantages of both HPLC and GC techniques because it may be readily employed in the analysis of nonvolatile and thermolabile compounds and provides facile coupling to detector technologies such as mass spectrometry and Fourier transform infrared (FT-IR) spectroscopy. In recent years, SFC has been used to separate flavonoid compounds, most of which are polymethoxylated flavones and polyhydroxylflavonoids. 

The concentration cA can be a measured variable if an analyzer (gas chromatograph, infrared spectrometer, etc.) is attached to the effluent stream. In many industrial plants such analyzers are not available because they are expensive and/or have low reliability (give poor measurements or break down easily). Consequently, in such cases cA is an unmeasured output variable. 

This continuous process is operated from a centralized control panel which contains more than one hundred recorders and controllers. In addition, a data-reduction system continuously scans 70 key temper ures and at intervals types them out on the plant log. If, in the scanning process, a deviation from control is noted, the operator is notified by an alarm and the deviating data are recorded automatically. The control panel also contains start-stop switches for all motors. Included in the instrumentations are an infrared analyzer on the nitric oxide stream, a hydrogen analyzer on the derivative autoclaves, and a mass spectrometer for nitroparaffin analysis. 

Of the few electroanalytical monitors the ones used in the chloralkali industry are worth mentioning.Sulphate was determined in brines. Oflf-line conductometry was used to determine sulphate in the concentration range 25 - 500 mM with Ba " as titrant, or Pb " " as titrant when potentiometric measurement was used. These methods can, however, not compete with infrared spectrophotometry in this application. Water was determined in chlorine gas by coulometry with 100 % current efficiency. In this case the analyzer should be installed very close to the production plant. 

In general, it is difficult to make online measurement of product quality it is often an inferred entity based on experience. The moisture content can be a measured variable if a suitable moisture sensor is used in the process. Analyzers are available for moisture analysis, which can be adapted for automatic, closed-loop dryer control. The most successful of these units rely on infrared, microwave, or capacitance detection [1]. Care must be exercised in the selection to allow for changes in bulk density or for void spaces, which will introduce an error. In many industrial-drying plants, such sensors are not available because either they are expensive or they have low reliability. Consequently, in such cases the moisture content is an unmeasured output variable. 

This same difference method is used to analyze for the various components in a closely specified blend of poly chlorobenzenes. To serve as a standard, an adequate supply of plant material was very accurately analyzed. This was accomplished by a careful fractional distillation, the fractions from which were analyzed by gas chromatography and by infrared methods. For calibration of the difference method, mixtures of the standard were made up with pure samples of the isomers to be determined. These mixtures were compared with the unaltered standard to obtain absorptivity data for equations similar to (8) above. 

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