The heat traced sample/umbilical will maintain the gases at an appropriate temperature all the way from the probe assembly to the analyzer shelter. Good engineering practice dictates that this be short as possible but it is of more importance to place the analyzer in a convenient location. Lengths up to 1,000 feet are possible. The sample umbilical bundle will contain one or more tubes for the sample gas and may contain additional tubes for instrument air and calibration gas. It may also have conductors and control wires for other functions needed at the Probe Assembly. The materials of the sample tube may be either Teflon or stainless steel depending on the temperature requirement. Typical monitored emissions include: sulfur dioxide, nitrogen oxides, carbon monoxide and volatile organic compounds. Wet-basis extractive gas analysis can be used to measure very wide variances in concentrations of total hydrocarbon, oxides of nitrogen, oxygen and moisture. For the measurement of very low levels of nitrogen oxides.