Sidestream monitoring

Both procedures provide different information with different significance. Depending on the application and the clinical situation, the advantages or disadvantages of one or other procedure may prevail. In anesthesia there is a trend to prefer multiparameter monitors for concentrations of O2, N2O, CO2, and agents. Therefore, a sidestream monitor may combine several separate sensors for different gases which utilize the same gas sample... 

Mass spectrometry offers the advantage of detecting all parameters of interest with the same delay. Influences caused by water or secretions are similar to those with other sidestream monitors. New generation devices avoid previous problems of vacuum technology, complicated handling, and calibration. The market potential remains uncertain. 

Chang, M.J., Walker, K., McDaniel, R.L. and Connell, C.T. (2005) Impaction collection and slurry sampling for the determination of arsenic, cadmium, and lead in sidestream cigarette smoke by inductively coupled plasma-mass spectrometry. Journal of Environmental Monitoring, 7(12), 1349-54. 

An improvement on the assessment of individual heat exchanger performance is to pass a sidestream through some kind of monitor. In general monitors resemble the test equipment used in the laboratory. The use of monitors allows a more careful control of the fouling conditions to be exercised particularly in terms of temperature, temperature changes and flow rates, using actual plant streams. The data obtained are more reliable than those obtained directly from the operation of full scale plant. 

Typical monitor data, such as response time, accuracy, or sensitivity, do not depend only on sensor characteristics. For example, the overall response time is composed of the sensor response time, of delays due to ambient influences such as water, of sample flow in the case of sidestream sensors, or of gas exchange time of the cell or detector volume. 

Mainly three types of oxygen sensors are used in clinical applications. Whereas the two electrochemical types have the largest market shares [12], paramagnetic sensors as the third type are important in combination with IR sensors for sidestream multi-gas analysis in anesthesia monitoring. Real multi-gas sensors such as mass spectrometers or Raman spectrometers are of minor importance. 

The sensor is applied in the sidestream, with a requirement to separate water to prevent unnoticed shifts of the measured value due to aspirated water. The main advantage is the possibility of an easy in-line combination with IR optical sensors which allow the essential anesthetic gases to be measured with one monitor in the sidestream. The fast response of this arrangement cannot be used to calculate derived parameters as the application in the side-stream generates undefined and changing delay times. 

To combine the advantages of both types, Nellcor designed a sensor see also Figure 23-20) which uses only 1 m of sample line and an extremely small sample cell and offers the advantage of short delay times of about 1 s, low flows of SO mL/min and short rise times of about S5 ms [23]. These features also offer acceptable monitoring of neonates. In practical use. the features arc slightly influenced by the normal problems in sidestream sensors with condensed water also which arc suposed to be overcome by (he proximal-diverting monitor. 

The humidity of the stream was controlled by a water bubble column and monitored by a Cambridge Systems Model 990 Thermoelectric Dew Point Hygrometer The sulfur dioxide concentration was regulated by manipulating three precision needle valves. The gas was analyzed with a Beckman Model 215A Infrared Sulfur Dioxide Analyzer equipped with a Sargent Model MR Chart Recorder. The humid gas mixture was then sent to a solenoid valve, which when activated permitted the stream to flow into the contact chamber. The flowrates of all the sidestreams are very small in comparison to the initial flowrate of nitrogen. Thus, the Initial flowrate can be considered as the effective flowrate into the contact chamber. 

The wash oil that is used for de-entrainment is also important for improving the separation between the bottom side stream and the resid stream. Separation is enhanced by condensation of the overflash by vaporizing the bottom sidestream. The amount of overflash that is required is affected by packing type, depth and source of the wash oil. Overflash flow rates should be carefully monitored to make sure that there is no degradation in the bottom side stream fractionation, that there is no increase in pitch entrainment to the heavy solvent neutral stream and there are no major increases in coking in the wash bed zone. 

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