Open-path monitoring of the atmosphere using Fourier transform infrared spectrometry has recently become a useful real-time in situ analytical technique. The U.S. Environmental Protection Agency (EPA) is currently formulating Method TO-16, a protocol for infrared remote sensing of the hazardous air pollutants (HAPs) identified in EPA’s Clean Air Act of 1990. To support infrared based sensing technologies, the National Institute of Standards and Technology (NIST) is currently developing a standard quantitative spectral database of the HAPs based on gravimetrically prepared samples. This paper presents the protocol used to prepare the gravimetric mixtures and initial results.