Infrared spectra of aqueous NO2( - ) and NO3( - ) solutions, and of binary mixtures, were recorded using internal reflection techniques and a Fourier transform spectrometer. NO2( - ) could be detected at a concentration of 0.02 M, and NO3( - ) at 0.001 M. However, NO3( - ) also became adsorbed on the Ge prism. After making corrections for adsorption and for overlapping of NO2( - ) and NO3( - ) bands, it was possible to analyze binary mixtures with concentrations as low as NO3( - ) = 0.03 M and NO2( - ) = 0.05 M. By adjusting the optics so that the usually totally absorbing water stretching band had a transmittance of about 50%, it was possible to observe N-H and C-H stretching bands of solutes. Dissolved materials cause distortions of the background which may influence qualitative and quantitative observations.