PORTABLE LED-ARRAY VIS-NIR SPECTROPHOTOMETER NEPHELOMETER/

A portable instrument with a high-speed multiple-wavelength LED array source, and simultaneous detectors for absorbance and 90 degrees nephe lometry, was tested from 420 to 950 nm. Absorbance values and simultan eous 90 degrees-scatter intensities at six different wavelengths can b e determined and stored every 0.02 s. An advantage of this LED instrum ent is that its sensitivity is equal to or better than many research-g rade spectrophotometers. Also, unlike diode array spectrometers, which emit white light through samples, the LED instrument emits monochroma tic light through samples, enabling us to obtain turbidity, turbidity ratio, and particle size information in addition to the absorption spe ctrum. Field applications can range from simple turbidity and multiple -wavelength absorbance measurements to kinetic experiments with tempor al acquisition of multiple-wavelength absorbance and simultaneous turb idity data. Rugged, laptop compatible, portable, and inexpensive, the LED instrument is useful for discrete or on-line VIS-NIR absorption an alysis and turbidity, or turbidity ratio, analysis. (C) 1998 John Wile y & Sons, Inc.