An optical cell for spectral analysis is disclosed generally comprising a monolithic cell body that transmits light, the cell body having an outer surface and a fluid channel for receiving a sample that defines an inner surface. The inner surface of said cell body includes a planar section, and the outer surface of said cell body likewise includes a planar section, which is adjacent and substantially parallel to the planar section of the inner surface. In certain embodiments, the ends of the channel are frustoconical, and ferrules are employed to secure sample inlet/outlet tubes to the cell.