Combustion Method with Infrared Absorption
Detection—A weighed test portion of sample is burned in a
tube furnace at a minimum operating temperature of 1350°C in
a stream of oxygen. During combustion at temperatures above
1350 ºC, the sulfur and sulfur compounds contained in the
sample are decomposed and oxidized almost exclusively to
gaseous sulfur dioxide, SO2. Moisture and particulates are
removed from the gas by filters. The gas stream is passed
through a cell in which sulfur dioxide is measured by an
infrared (IR) absorption detector. Sulfur dioxide absorbs IR
energy at a precise wavelength within the IR spectrum. Energy
is absorbed as the gas passes through the cell body in which the
IR energy is being transmitted: thus, at the detector, less energy
is received. All other IR energy is eliminated from reaching the
detector by a precise wavelength filter. Thus, the absorption of
IR energy can be attributed only to sulfur dioxide whose
concentration is proportional to the change in energy at the
detector. One cell is used as both a reference and a measurement
chamber. Total sulfur as sulfur dioxide is detected on a
continuous basis.