Photonics Finds Solvents in Water

Kevin Robinson

With the list of Superfund sites growing almost daily, the need for a reliable technique to test water samples on-site also increases. Researchers at Ohio University believe that near-IR spectrometers may have what it takes to be robust field-testing instruments. The group, led by Gary W. Small, has demonstrated that the technique can detect in water the presence of two solvents commonly used in nuclear fuel reprocessing.

"We wanted to investigate a technique that has the potential to be field-portable and could be low-cost, compact, rugged and reliable," Small said. "We wanted to use a technique that could analyze the water samples without any pretreatment or any chemical reagents."

The group tested near-IR absorption spectroscopy and single-beam spectroscopy with water containing tributyl phosphate and methyl isobutyl ketone. Using a Digilab FTS-60A Fourier transform spectrometer from Bio-Rad Laboratories Inc. of Cambridge, Mass., to collect the spectra, they added both chemicals to reagent water.

To more closely approximate field conditions, the group, whose work was funded by Argonne National Laboratory in Argonne, Ill., also added the chemicals to some samples from the Hocking River in Athens.

Although absorbance spectroscopy is more accurate, single-beam spectroscopy does not require a reference measurement, explained Small. "This would be advantageous if you were working in the field. We wanted to evaluate whether we could get similar results with single-beam spectra, and we did."

The researchers, whose report appeared in Applied Spectroscopy, Vol. 54, No. 7, found that they were able to determine the presence of the two chemicals in concentrations from 1 to 100 ppm, with an average error of 4 ppm. "These results establish the viability of NIR spectroscopy for measuring these solvents in water samples," Small said.

The commercialization of a field-portable device depends on the identification of specific applications that require such a screening tool. "Most organic compounds have a response in the near-infrared region of the spectrum," he said. "A similar approach could be used for other compounds in water samples."