Abstract
The global demand for natural products grows rapidly, intensifying the request for the development of high-throughput, fast, non-invasive tools for quality control applicable on-site. Moisture content is one of the most important quality parameters of natural products. It determines their market suitability, stability and shelf life and should preferably be constantly monitored. Miniaturized near-infrared (NIR) spectroscopy is a powerful method for on-site analysis, potentially fulfilling this requirement. Here, a feasibility study for applicability and analytical performance of three miniaturized NIR spectrometers and two benchtop instruments was evaluated in that scenario. The case study involved 192 dried plant extracts composed of five different plants harvested in different countries at various times within two years. The reference analysis by Karl Fischer titration determined the water content in this sample set between 1.36% and 6.47%. For the spectroscopic analysis half of the samples were laced with a drying agent to comply with the industry standard. The performance of various calibration models for NIR analysis was evaluated on the basis of root-mean square error of prediction (RMSEP) determined for an independent test set. Partial least squares regression (PLSR), Gaussian process regression (GPR) and artificial neural network (ANN) models were constructed for the spectral sets from each instrument. GPR and ANN models performed superior for all samples measured by handheld spectrometers and for native ones analyzed by benchtop instruments. Moreover, the accuracy penalty when analyzing native samples was lower for GPR and ANN prediction as well. With GPR or ANN calibration, miniaturized spectrometers offered the prediction performance at the level of the benchtop instruments. Therefore, in this analytical application miniaturized spectrometers can be used on-site with no penalty to the performance vs. laboratory-based NIR analysis.
Highlights
In recent years, the interest in miniaturized handheld near-infrared (NIR) spectrometers for fast, non-invasive and, most importantly, laboratory independent measurements has increased tremendously
The MicroNIR 2200 and MicroNIR 1700ES instruments are designed around a linear variable filter (LVF) technology used for the wavelength selector element
This study suggests NIR spectroscopy as an alternative for KarlFischer (KF) titration
Summary
In recent years, the interest in miniaturized handheld near-infrared (NIR) spectrometers for fast, non-invasive and, most importantly, laboratory independent measurements has increased tremendously Their applicability is largely depending on the analytical problem at hand [1]. No systematic performance investigations involving several miniaturized and benchtop instruments have appeared in literature It was the aim of this work to perform a systematic feasibility study comparing the prediction performance of three handheld and two benchtop instruments hyphenated to PLSR, GPR and ANN analysis. For this purpose, a challenging case of the moisture content determination in a chemically complex and varying sample matrix (a mixture of different dried plant extracts) was selected
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