Sulfur Dioxide Detector Tube

Sulfur Dioxide Pass 1050 50 mL of sample, taken from the liquid phase as described in the test for Nitric Oxide and Nitrogen Dioxide, through a sulfur dioxide detector tube (see Detector Tubes) at the rate specified for the tube. The indicator change corresponds to not more than 5 ppm Volatile Hydrocarbons... 

Sulfur Dioxide. Both flame photometric and pulsed fluorescence methods have been applied to the continuous measurement of S02 from aircraft. In the flame photometric detector (FPD), sulfur compounds are reduced in a hydrogen-rich flame to the S2 dimer. The emission resulting from the transition of the thermally excited dimer to its ground state at 394 nm is measured by using a narrow band-pass filter and a photomultiplier tube. 

An on-line analyzer must be packaged much more robustly than a laboratory instrument to withstand the process environment which, for example, may have an explosive atmosphere and significantly variable ambient temperature. It must also be capable of continuous, unattended operation over long periods of time. Clearly, the simpler the instrument the better. Of the methods listed in Table 1, WDXRF, polarized EDXRF, and Pyro-microcoidometry have not been adsqrted to on-line process instrumentation, whereas the other methods have. The relative simplicity of Pyro-EC makes it particularly suitable for adaptation to process instrumentation. The sulfur dioxide sensor is a small, plug-in, low cost electrochemical cell, easily replaceable and with an expected lifetime of over one year. The UV lamp, UV optics, and photomultiplier used in Pyro-UVF are not required. The X-ray tube (or radioactive source). X-ray detector, and X-ray optics used in all the XRF instruments are not required. 

Detector Tubes for Measuring Gaseous Pollutants Detector tubes, such as stain tubes and passive sampler tubes, are simple measurement devices that are available for the gaseous pollutants—CO, CO2, NO, and NO2—and for sulfur dioxide (SO2). Detector tubes are simple and cost effective and may be useful for characterizing air quahty. However, they do not provide sufficient accuracy as a measurement technique if accuracy greater than 25% is required. 

Typically, sulfur dioxide and mercaptans may cause positive interferences. In some cases, nitrogen dioxide can cause a native interference. Most detector tubes will have a precleanse layer designed to remove certain interferences up to some maximum interferent level. Consult manufacturers instructions for specific interference information. 

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