Abstract: An apparatus and method for analyzing liquid samples employs first and second bidirectional ports that permit liquids to be introduced to first and second liquid waveguide capillary cells at the same time. The direction of liquid flow through the apparatus and roles of components may be reversed to prevent or overcome obstruction by particulates and other debris. The apparatus and method can detect and map colored dissolved organic matter and can detect, discriminate and map algal species or algal blooms including red tide in an automated, unattended manner within large aquatic systems.