A method for determining siloxane content of a gas by non-dispersive infrared analysis including the steps of providing infrared light at a limited wave number band selected according to the absorption bands of the siloxanes, transmitting the infrared light at the limited wave number band to a volume of a gas to be analyzed, and detecting the intensity of the infrared light at the limited wave number band passed through the volume of a gas to be analyzed. The siloxane content is determined based on the absorption of the infrared light at the limited wave number band. Preferably, the limited wave number band lies in the range of 800 to 860 cm−1.