Fiber Optic Sensors and Chemometric Analysis

Description:
Near-infrared (NIR) spectra of samples are collected with silica optical fibers. Chemometric analysis of the spectra significantly improves detection capabilities.

Broad Fields of Use:
NIR spectra collected with fiber optic sensors allow analysis of materials in inaccessible locations and hostile environments. The sensors are tolerant of hot and cold temperatures, radiation, and corrosive and flammable environments. The sensors fit in small spaces and only small sample volumes are needed. The sensors work with liquids and slurries and are well-suited for process monitoring, flow systems, and reacting systems.

Chemometric analysis allows detection of sample components that do not have any direct absorption by extracting information on how they influence the spectral features of the components of the sample with NIR absorption features.

Figure 1. NIR spectrum of 1 µL of kerosene using a 600 µm diameter fiber sensor.

Comparison with Current Technologies:
The combination of fiber optic sensors and chemometric analysis of near infrared spectra allows rapid, in situ analysis of liquids and slurries in flow systems, reactors, and a number of other difficult environments. Collecting and analyzing samples by conventional laboratory analysis can be difficult, time-consuming, and expensive. Small, inexpensive fiber optic sensors can be placed in contact with the sample material for rapid, in situ analysis. Continuous monitoring of flow samples can be readily performed.

Description of Current Application:
This analytical technique was developed as a straightforward and cost-effective method to analyze the chemical components of nuclear wastes stored in tanks at Department of Energy facilities. The development was conducted with waste simulants consisting of a complex mixture of highly alkaline aqueous solutions, inorganic salts, and organic compounds. We developed methods that provided accurate analysis of the major components of the simulant mixtures, including total organic carbon. These methods readily lend themselves to the analysis of slurries. The fiber optic sensors that were developed could be used to analyze sample volumes as small as one microliter. Additionally, we demonstrated that the fibers are highly resistant to gamma radiation.

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