Solid Phase Extraction Using C-18 Sorbents to Treat Organics in Water and Eliminate Spectral Interference in Isotope Ratio Infrared Spectroscopy

Abstract:

Although isotope ratio infrared spectroscopy (IRIS) provides an inexpensive, convenient instrumentation for water isotope analysis, analyzing δ²H and δ¹⁸O becomes much less accurate if the water contains organic contaminants. Alcohols such as Ethanol and Methanol cause significant changes in the apparent isotope values such that the more these species are present in the water, the more erroneous the IRIS data becomes. Although activated charcoal and pre-combustion methods have typically been used to mitigate this inaccuracy, a new application of Solid Phase Extraction (SPE) using C-18 sorbents shows promising results in eliminating more organics and reducing spectral interferences more than current treatment techniques. SPE’s can be prepared in the field and can quickly treat samples upon collection: this study focuses on developing a consistent method for use both in field and lab to allow isotope hydrology measurements to be unhampered by potential organics. To study the adsorption effect of SPE’s, we used H-NMR technology to calculate absolute concentrations of Ethanol and Methanol in water pre- and post- treatment. SPE removed up to 90% Ethanol and 60% Methanol in water, and the corresponding measured isotopic values after alcohol removal were much closer to the pure water reference.