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

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 Rval(2) 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.