A main stream gas analyzing device for measuring a concentration of a trace gas present in a gas stream and a method of measuring the concentration of the trace gas is disclosed. The main stream gas analyzing device includes a measuring chamber for receiving a gas flow, an infrared reflective material provided on an inner surface of the measuring chamber, an infrared radiation source directed toward the infrared reflective material of the measuring chamber and obliquely angled relative to a longitudinal axis of the measuring chamber such that infrared radiation being emitted from the infrared radiation source is reflected off of the infrared reflective material at least once, and an infrared radiation detector obliquely angled relative to the longitudinal axis of the measuring chamber to receive the reflected infrared radiation.
