Chromium is an essential nutrient in its trivalent oxidation state, but carcinogenic in its hexavalent oxidation state. Although current water regulations provide for limits on total chromium, the deeper concern is the concentration of the hexavalent chromium, or chromate, species. The economic impact of potential regulation must be considered when new rules are promulgated, and the cost of testing is an important piece of the cost equation. Analytical methods that elucidate the chromate concentration from total chromium are therefore an important tool. New methods that reduce testing costs will enable tighter regulations and improve water quality. Raman spectroscopy can be amplified by the use of noble metal nanoparticles. These nanoparticles increase the efficiency of Raman scattering by three to nine orders of magnitude. This signal enhancement allows detection of a wide variety of molecules down to trace concentrations. Coined surface-enhanced Raman spectroscopy (SERS), this effect was first discovered in the 1970’s and has been widely studied as a potential analytical tool. We describe here a SERS-based method for the quantification of hexavalent chromium in water samples. This method couples with internal standards for quantification with linker molecules for chromate specificity, resulting in a simple method for low-ppb quantitation in real-world samples. Due to the internal standard, once a calibration curve is generated, the method is stable across spectrometers and over time, enabling fast, accurate analysis with minimal testing time.

Quantitative analysis of hexavalent chromium using surface-enhanced Raman spectroscopy

ACS Spring Meeting 2021

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