Scientifically operated CCD-based spectroscopic system for high-precision spectrometric determinations of seawater

The application of an aberration-corrected imaging spectrograph with the use of fiber-optic inputs and a charge-coupled device detector to produce a sensitive, flexible, and rugged spectroscopic system capable of employment in remote sensing and held applications is presented. This investigation focuses on the optical system design, detector characteristics, and modes of operation that will result in a field instrument capable of both sensitive fluorescence and high-precision absorbance measurements. Evaluation of the optical system used the spectroscopic determination of seawater pH as the test case. Spectral measurements were made with the use of thymol blue as a pH indicator for absorbance and 7-hydroxy-coumarin as the fluorescence pH indicator. This system displayed excellent precision for both absorbance and fluorescence analyses; RSDs for absorbance and fluorescence of +/-0.00065 and +/-0.0015 in pH, respectively, were experimentally obtained. These findings, along with the advantages of the area array detector to provide simultaneous multiwavelength, multianalyte spectral analysis in a single, rugged optical system, make a strong case for the application of scientifically operated solid-state detector systems to remote sensing and field instrumentation.