Critical evaluation of spectral information of benchtop vs. portable near-infrared spectrometers: quantum chemistry and two-dimensional correlation spectroscopy for a better understanding of PLS regression models of the rosmarinic acid content in Rosmarini folium

Abstract

In the present work the performances of one benchtop and two different types of miniaturized near-infrared (NIR)-spectrometers were tested and compared for the first time by the determination of the rosmarinic acid (RA) content of dried and powdered Rosmarini folium. The recorded NIR spectra were utilized in hyphenation with multivariate data analysis (MVA) to calculate Partial Least Squares (PLS) regression models. Quality parameters obtained from Cross Validation (CV) revealed that the benchtop NIR-device "NIRFlex N-500 FT-NIR spectrometer" achieved the best result with a R of 0.91 and a RPD of 3.27. The miniaturized NIR-device "MicroNIR 2200 spectrometer" showed a satisfying calibration quality with a R of 0.84 and a RPD of 2.46. The miniaturized NIR-device "ThermoScientific microPHAZIR" with a R of 0.73 and a RPD of 1.88 was less precise and needs to be improved. The measured spectra of the different devices were additionally investigated by two-dimensional correlation spectroscopy (2D-COS) analysis, which supported the performed PLS regression models as well as identified the discrepancies for microPHAZIR and MicroNIR 2200 compared to NIRFlex N-500. With the aim to obtain a better understanding of the factors which determine the analyzed PLS regression models, the NIR spectrum of RA was reproduced through application of fully anharmonic quantum chemical calculation. A good agreement between the experimental and theoretical NIR spectra and detailed band assignments of RA were obtained in the 8000-4000 cm wavenumber region. Subsequently, this enabled us to attribute the main influences in the regression coefficients plots. This study demonstrated that the performance of NIR spectroscopy with benchtop and miniaturized devices as a fast and non-invasive technique is able to replace time- and resource-consuming analytical tools. Referring to the developed application of the RA content quantification this work is especially interesting for the continuous growing phytopharmaceutical industry and its quality control. The results reveal the importance of monitoring the performances of available NIR-spectrometers in every analytical area.

Critical Evaluation of NIR and ATR-IR Spectroscopic Quantifications of Rosmarinic Acid in Rosmarini folium Supported by Quantum Chemical Calculations

“…Therefore, the assignment of the major contributions in the regression coefficients plot (▶ Fig. 7) to the most probable vi-brations of RA was done referring to Kirchler et al [37]. Bands which could not be connected to the calculated RA spectrum were assigned in a general way (indicated by g) according to Workman and Weyer [34] or have no assignment (n.…”

Determination of the clean‐up efficiency of the solid‐phase extraction of rosemary extracts: Application of full‐factorial design in hyphenation with Gaussian peak fit function

“…The aliquots were combined and adjusted to 25 mL with the extracting solvent. After a last centrifugation step the extracts of each plant sample were stored at –80°C .…”

Theoretical and technical advancements of near infrared spectroscopy and its operational impact in industry

“…Kirchler et al described the critical evaluation of spectral information of benchtop vs portable NIR spectrometers, conducting quantum chemistry and 2D-COS for a better understanding of PLS regression models of the rosmarinic acid content in Rosmarini folium. 12 Henn et al performed a similar study determining the performance of minia-turizations on melamine in milk powder 13 and compared the sensitivity to artificial spectral errors and multivariate LOD. The best RMSEP values were 0.28 g/100 g, 0.33 g/100 g and 0.27 g/100 g for the NIRFlex N-500, the portable/miniaturized spectrometers microPHAZIR and the microNIR2200, respectively.…”

“…The critical performance evaluation of benchtop and miniaturized spectrometers for the quantitative analysis of rosmarinic acid in Rosmarini folium conducting 2D-COS and quantum chemical calculations has already been summarized. 12 The possibilities employing spectral imaging for medicinal plant quality control have been recently reviewed by Türker-Kaya et al 19…”