An apparatus for measuring concentrations of a first vapor pressure carrier fluid component and a second vapor, pressure carrier fluid component in a carrier fluid mixture, including a supply vessel for holding the carrier fluid mixture. A light source is provided for transmitting an infrared light source to the carrier fluid mixture. Detector is provided for detecting infrared light intensity transmitted through the carrier fluid mixture, and, in response thereto, determining infrared absorption of carbon hydrogen stretching frequencies of the carrier fluid mixture. And means are provided for calculating concentrations of the first carrier fluid component and the second carrier fluid component in the mixture based on the infrared absorption of carbon hydrogen stretching frequencies of the carrier fluid mixture. This method can also be extended to a mixture of more than two fluids. A means for maintaining a predetermined ratio of the carrier fluids.