PNNL

Abstract

Microfluidic devices (MFDs) are a customizable, low cost, and low waste platform for performing chemical analyses. Optical spectroscopy techniques provide a nondestructive way to monitor small sample volumes within microfluidic channels. Optical spectroscopy can probe speciation, oxidation state, and concentration of analytes, as well as detecting counterions and providing information about matrix composition. Here, UV-visible absorbance, NIR absorbance, and Raman spectroscopy are utilized on a custom PMMA MFD for the detection of three lanthanide nitrates in solution. The absorbance spectroscopies are conducted across three pathlengths using three portions of a contiguous channel within the MFD. Univariate and chemometric multivariate modeling, specifically principal component regression (PCR), is utilized to quantify the three lanthanides and the nitrate counterion. Models are composed of spectra from one or multiple pathlengths. Models are also constructed from multiblock spectra comprised of UV-vis, NIR, and Raman spectra at one or multiple pathlengths. While univariate modeling produces acceptable results for analytes with a simple signal, such as samarium cations, multivariate and multiblock models produce enhanced quantification for analytes such as holmium, which experience spectral overlap and interfering non-analyte signals.