Reproducible quantification of ethanol in gasoline via a customized mobile near-infrared spectrometer

•Efficient and cost-effective customizations of a novel miniature NIR spectrometer.•Highly reproducible prediction of the bio-ethanol amount admixed to gasoline.•Computational band assignment of the NIR absorption bands.•Thorough comparison of four alternative measurement modes.

This work describes the modification of an InGaAs diode array detector equipped miniaturized near-infrared (NIR) spectrometer enabling the reliable quantification of ethanol blended gasoline. A transflectance measurement cell is presented, utilizing a thermoelectric cooling (TEC) appliance ensuring thermostatic measurement conditions and a gold-coated spherical mirror as a reflector superior to conventional Spectralon®. In total, four measurement modes (Spectralon® reflector, gold reflector and either reflectors with employed TEC) are discussed, enabling a straightforward comparison of the results. The test-set validated multivariate partial least squares regression (PLSR) model of the measurement mode involving both gold mirror and TEC yielded an Rval2 value of 0.997, a limit of detection (LOD) of 0.68% w/w, a limit of quantification (LOQ) of 2.04% w/w, a standard error of prediction (SEP) of 0.21% w/w and a ratio performance deviation (RPD) of 15.2 while utilizing a single latent variable (LV). The NIR band assignment in this work has been established by employing the vibrational self-consistent field second order perturbative treatment (PT2-VSCF) and the computationally derived absorption maxima are compared to the experimentally observed data.

Graphical abstractFigure optionsDownload full-size imageDownload as PowerPoint slide