The performance of a portable near infrared spectrophotometer to determine biodiesel content in diesel/biodiesel
blends, as well as to quantify adulteration by vegetable oil, was evaluated. The NIR transmittance/absorbance
spectra of 118 samples in the range 950–1650 nm were acquired using an
ultra-compact spectrophotometer (MicroNIR), and also by using a Fourier transform benchtop instrument
(FT-NIR) from 800 to 2500 nm. In a preliminary step, partial least squares (PLS) models aimed at
the determination of biodiesel quality parameters were developed by using full spectral information.
Thereafter, the variables showing significant regression coefficients were selected and the PLS models
were re-processed. Successive Projections Algorithm (SPA) was used to screen for the most orthogonal
variables to be used in a model constructed by using Multiple Linear Regression (MLR). For determining
the contents of both biodiesel and vegetable oil in diesel/biodiesel blends, using MicroNIR and FT-NIR, the
results indicated MLR-SPA as the best modelling strategy. RMSEP values of 0.22% v/v (MicroNIR) and
0.13% v/v (FT-NIR) for biodiesel and 0.34% v/v (MicroNIR) and 0.22% (FT-NIR) for vegetable oil contents
were obtained. LOD values of 0.31% (MicroNIR) and 0.22% (FT-NIR) for biodiesel and 0.40% (MicroNIR)
and 0.34% (FT-NIR) for vegetable oil determination were achieved. The results revealed comparable performances
between the portable and the benchtop instruments, demonstrating the feasibility of monitoring
in situ the quality characteristics of diesel/biodiesel blends according to biodiesel content and for
detection of adulteration with vegetable oils by using the portable spectrophotometer.
The performance of a portable near infrared spectrophotometer to determine biodiesel content in diesel/biodieselblends, as well as to quantify adulteration by vegetable oil, was evaluated. The NIR transmittance/absorbancespectra of 118 samples in the range 950–1650 nm were acquired using anultra-compact spectrophotometer (MicroNIR), and also by using a Fourier transform benchtop instrument(FT-NIR) from 800 to 2500 nm. In a preliminary step, partial least squares (PLS) models aimed atthe determination of biodiesel quality parameters were developed by using full spectral information.Thereafter, the variables showing significant regression coefficients were selected and the PLS modelswere re-processed. Successive Projections Algorithm (SPA) was used to screen for the most orthogonalvariables to be used in a model constructed by using Multiple Linear Regression (MLR). For determiningthe contents of both biodiesel and vegetable oil in diesel/biodiesel blends, using MicroNIR and FT-NIR, theresults indicated MLR-SPA as the best modelling strategy. RMSEP values of 0.22% v/v (MicroNIR) and0.13% v/v (FT-NIR) for biodiesel and 0.34% v/v (MicroNIR) and 0.22% (FT-NIR) for vegetable oil contentswere obtained. LOD values of 0.31% (MicroNIR) and 0.22% (FT-NIR) for biodiesel and 0.40% (MicroNIR)and 0.34% (FT-NIR) for vegetable oil determination were achieved. The results revealed comparable performancesbetween the portable and the benchtop instruments, demonstrating the feasibility of monitoring
in situ the quality characteristics of diesel/biodiesel blends according to biodiesel content and for
detection of adulteration with vegetable oils by using the portable spectrophotometer.
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