Laptop chemistry: A fiber-optic, field-portable, near-infrared spectrometer

We describe a fiber-optic, field-portable spectrophotometer for measurement in the near-infrared (NIR) (680–1050 nm) region of the spectrum. This instrument, bundled with a laptop computer for data acquisition and statistical analysis, has a footprint of only 6 in.×14 in.×18 in. and weights approximately 20 pounds. The instrument uses the single beam measurement principle by employing a grating-based spectrograph for wavelength dispersion and a silicon photodiode-array (PDA) as detector. A computer-controlled, optically stabilized 5.5-W tungsten lamp is used as the light source. Sample measurements are made with a bifurcated fiber bundle for noninvasive diffuse reflectance and/or transflectance measurements. The portable spectrometer attains an RMS signal-to-noise ratio of 1.24×10−5 AU, stray light intensity levels of 0.1%, spectral resolution of 25 nm, and a dynamic range of approximately three orders of magnitude. The analysis of three-component hydrocarbon mixtures by transflectance NIR spectroscopy is demonstrated.