A dual-mode method and apparatus of selectively measuring samples in either a vessel or as a surface tension retained sample held between two opposing pedestals is introduced. In either configuration, such modes further contain optical paths from a source system through a small-volume or large-volume sample to a spectrometer based system. Such a system enables a user to measure samples with absorbances ranging from about 0.005 up to about 2.0 Absorbance Units for any given wavelength.