Significant needs exist for on-line real-time monitoring of water quality and hydroponic plant nutrients in regenerative life support systems. Toxic metals and organic pollutants in recirculated water are more effectively controlled by on-line monitoring. Biomass production of various crops may be enhanced by optimal control of plant nutrients. A new on-line fiber optic spectrometer is in development that uses a combination of ultraviolet-visible absorption measurements in combination with liquid atomic emission spectra to assay a wide variety of chemical compounds and ions in solution. Problems created by interfering, overlapping spectra are solved through the use of pattern recognition methods for multicomponent chemical analysis. This analytical instrument has been successfully applied to the analysis of 15-component plant nutrient solutions.