Pathlength effects on NIR Transflectance performance for polar and apolar liquid food analysis

Area of Science:

• Analytical Chemistry
• Spectroscopy
• Chemometrics

Background:

• Near-infrared (NIR) transflectance spectroscopy is a valuable tool for food analysis.
• The influence of accessory pathlength on spectral quality and chemometric model performance in NIR spectroscopy remains underexplored.
• Systematic evaluation is needed to optimize pathlength selection for diverse sample matrices.

Purpose of the Study:

• To investigate the effect of accessory pathlength (1-6 mm) on spectral characteristics.
• To assess the impact of pathlength on partial least squares regression (PLSR) model accuracy for two distinct liquid food systems.
• To provide practical guidance for pathlength selection in NIR spectroscopy applications.

Main Methods:

• Acquisition of NIR spectra (10,000-4000 cm⁻¹ and 7407-3921 cm⁻¹) using benchtop and handheld FT-NIR spectrometers.
• Evaluation of four pathlengths (1, 2, 4, 6 mm) in two liquid matrices: apolar olive oil (adulterated) and polar methanol-spiked vodka.
• Analysis of spectral data and PLSR model performance (SEP, r, RPD) to determine optimal pathlengths.

Main Results:

• In apolar olive oil, longer pathlengths (4-6 mm) enhanced spectral features and improved %GPOO prediction accuracy (SEP=0.56%, RPD=52.6).
• In polar methanol-vodka, the 1 mm pathlength was optimal to avoid spectral saturation from OH absorption, yielding high accuracy (SEP=0.036%, RPD=47.2).
• Handheld NIR devices showed similar trends but lower predictive performance compared to benchtop instruments.

Conclusions:

• Accessory pathlength is a critical parameter influencing NIR spectral quality and chemometric model performance.
• Optimal pathlength selection is matrix-dependent: intermediate-to-long paths (4-6 mm) for apolar samples and short paths (1 mm) for polar samples.
• These findings provide essential practical guidance for optimizing NIR spectroscopy method development in food analysis.