Instrumentation and Control Systems 683 MAGNETIC SEPARATOR FOCUSING DETECTOR SOURCE Figure 3. Magnetic deflection principle. The quadrapole mass spectrometer also employs an electron beam to ionize the particles using the quadrapole instead of a magnet to deflect the path of the particles and filter out all but the specific component to be analyzed. The quadrapole is a set of four similar and parallel rods(see Fig 4)with opposite rods electrically connected. A radio frequency and dc charge of equal potential, but opposite charge, is applied to each set of the rods. By varying the absolute potential applied to the rods, it is possible to eliminate all ions except those of a specific mass-to-energy ratio. Those ions which successfully travel the length of the rods strike a Faraday plate which releases electrons to the ions thereby generating a measurable change in EMF. For a given component the strength of the signal can be compared to references to determine the concentration The quadrapole, when used in conjunction with a gas chromatograph to separate the components, can measure a wide range of gases, typically fror 50 to 1000 atomic mass units(amu) mass spectrometers are relatively expensive, the exhaust gas of three or more bioreactors is typically directed to a single analyzer. This is possible because the offgas analysis is done outside the bioreactors them- selves. However, the multiplexing of the streams results in added complexity with regard to sample handling and routing, particularly if concerns of cross contaminationneed be addressed The contamination issue is usually handled by placing ultrafilters in the exhaust lines. Care, however, must be taken toInstrumentation and Control Systems 683 Figure 3. Magnetic deflection principle. The quadrapole mass spectrometer also employs an electron beam to ionize the particles using the quadrapole instead of a magnet to deflect the path of the particles and filter out all but the specific component to be analyzed. The quadrapole is a set of four similar and parallel rods (see Fig. 4) with opposite rods electrically connected. A radio frequency and dc charge of equal potential, but opposite charge, is applied to each set of the rods. By varying the absolute potential applied to the rods, it is possible to eliminate all ions except those of a specific mass-to-energy ratio. Those ions which successfidly travel the length ofthe rods strike a Faraday plate which releases electrons to the ions thereby generating a measurable change in EMF. For a given component the strength of the signal can be compared to references to determine the concentration. The quadrapole, when used in conjunction with a gas chromatograph to separate the components, can measure a wide range ofgases, typically from 50 to 1000 atomic mass units (amu). As mass spectrometers are relatively expensive, the exhaust gas of three or more bioreactors is typically directed to a single analyzer. This is possible because the offgas analysis is done outside the bioreactors them￾selves. However, the multiplexing ofthe streams results in added complexity with regard to sample handling and routing, particularly if concerns of cross contamination need be addressed. The contamination issue is usually handled by placing ultrafilters in the exhaust lines. Care, however, must be taken to