The measurement of millimolar levels of dissolved oxide in both basic and acidic molten sodium chloroaluminate salts by infrared spectroscopy is described. Both emittance and external reflectance sampling modes were employed using diamond-windowed cells to record infrared spectra of melt solutions containing varying amounts of oxide. Correlation between infrared emittance at 680 and 801 cm-1 (basic melts) and oxide concentration determined by a voltammetric method showed a linear relation (r=0.998) over the range 0-300 mM. Finally, standard addition measurements on acidic melts not amenable to the voltammetric method yielded values for oxide content that were reasonable given the preparative procedures.