Characterization of Hazardous Aqueous Samples by Near-IR Spectroscopy

We describe the application of near-infrared spectroscopy to determine the chemical composition of aqueous samples that simulate hazardous wastes at the DOE Hanford site. Surrogate liquid mixtures are prepared with compositions similar to the actual Hanford liquid wastes. We demonstrate a standard error of precision of approximately 0.06 M for NaNO3 and NaNO2, 0.006 M for Na3HEDTA, and 0.009 M for Na2CO3 by using a 1 mm pathlength and approximately 1 min collection time in the 9000–5400 cm−1 (1.11–1.85 μm) region. Even though most of these electrolytes do not possess characteristic near-infrared bands suitable for quantitative analysis, the use of partial least-squares multivariate calibration makes it possible to correlate spectral differences, based on perturbations in the near-IR water spectrum, and determine each component concentration. The effects of the electrolytes and temperature on the water spectrum are discussed.