Determination of ammonia in environmental samples using the diode laser/fiber optic colorimetric spectrometer

To analyze aqueous ammonia, we develop a simple and inexpensive spectrometer that consisted of a diode laser, optical fibers and a photodiode detector. The concentrations of ammonia are determined by the indophenol blue method. Preliminary results on the performance of the system in terms of the stability of output intensity, linearity of a calibration curve, and the determination of ammonia in environmental samples are described. The measured concentrations are also compared with those on a conventional spectrometer. The results indicate the potential to develop a portable spectrometer useful for on-site monitoring of environmental samples. Diode lasers are favored due to the monochromatic and high intensity radiation, and the reduction of heavy and expensive components in available commercial spectrometers. For the tested on-site analyzer, a photomultiplier tube, a monochromator, and complicated optical alignments are not required. (C) 2000 Society of Photo-Optical Instrumentation Engineers. [S0091-3286(00)01807-9].