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° nephelometry, was tested from 420 to 950 nm. Absorbance values and simultaneous 90°-scatter intensities at six different wavelengths can be determined and stored every 0.02 s. An advantage of this LED instrument is that its sensitivity is equal to or better than many research-grade spectrophotometers. Also, unlike diode array spectrometers, which emit white light through samples, the LED instrument emits monochromatic light through samples, enabling us to obtain turbidity, turbidity ratio, and particle size information in addition to the absorption spectrum. Field applications can range from simple turbidity and multiple-wavelength absorbance measurements to kinetic experiments with temporal acquisition of multiple-wavelength absorbance and simultaneous turbidity data. Rugged, laptop compatible, portable, and inexpensive, the LED instrument is useful for discrete or on-line VIS–NIR absorption analysis and turbidity, or turbidity ratio, analysis. © 1998 John Wiley & Sons, Inc. Field Analyt Chem Technol 2: 21–28, 1998