Method of determining the component of a gas in a gas sample

An arrangement for determining the portion of a gaseous or vaporous component in a gas mixture, the arrangement comprising:

• a channel for conducting a constant volume flow of said gas mixture therethrough and containing a detecting substance which can enter a chemical reaction with said component to produce a coloration of said detecting substance;
• means for transmitting radiation to a defined spatially fixed length segment of said channel;
• means for receiving radiation reflected from said length segment to form a reflectance signal I(t);
• and,
• an evaluation unit for receiving said reflectance signal I(t) and being adapted for doing the following:
• determining a slope .DELTA.I/.DELTA.t at the start of said chemical reaction during a time interval .DELTA.t in which said detecting substance is present in excess;
• determining a saturation reflectance signal I.sup.100% toward the end of said chemical reaction which corresponds to an almost complete chemical conversion of said detecting substance within said length segment;
• and, determining a normalized slope in correspondence to the formal relationship
• .DELTA.I/(I.sup.100% *.DELTA.t)
• which is proportional to said portion of said gaseous or vaporous component.