A PORTABLE COLORIMETER USING LIGHT-EMITTING-DIODES AND PHOTODIODES WITH FAST-FOURIER-TRANSFORMATION SIGNAL-PROCESSING

A portable colorimeter equipped with light-emitting diodes (LEDs) and two photodiodes (PDs) as light sources and detectors, respectively, wa s developed. LEDs were electronically modulated with square waves, Lig ht from an LED was divided by optical fibers and conducted to a sample and reference cell. The sample or reference light was detected by eac h PD. Then detected signals were fed to a notebook computer through a dual-channel analog-to-digital converter. Neither monochromator nor ba ndpass filter was necessary, because an LED's spectral bandwidth is re latively narrow. A signal from an LED in the time domain was converted into a frequency-domain signal by fast Fourier transformation on a co mputer. Absorbance was calculated from intensities of sample and refer ence signals. This colorimeter was successfully applied to the determi nation of cobalt in a synthetic water sample and to the on-site analys is of nitrite ions in river water. (C) 1998 John Wiley & Sons, Inc.