Standardisation of near Infrared Spectrometers: Evaluation of Some Common Techniques for Intra- and Inter-Brand Calibration Transfer

Six standardisation methods (direct standardisation, piecewise direct standardisation, robust standardisation, slope and bias and bias only post regression correction and no standardisation or spectral pre-treatment only) were compared for the transfer of whole soybean protein, oil and linolenic acid models. Two Foss Infratec and two Bruins OmegAnalyzerGs instruments were used to evaluate the standardisation methods in intra- and inter-brand scenarios. Each instrument was calibrated on its own calibration set for comparison. Partial least squares was used to develop all models. For each brand, a master was selected and the calibrations developed on it were transferred to the secondary unit of its own network (intra-brand transfer) and to the two units of the other brand (inter-brand transfer). Foss Infratec models were transferable to Bruins OmegAnalyzerG units with a similar or better precision than when all instruments were calibrated on their own calibration sets and vice versa. Optical standardisation methods (techniques that modify spectra of secondary units to match those of the master unit) performed significantly poorer than other methods. Other techniques provided similar results. Pre-processing of the spectra with or without simple treatment of the predictions was sufficient to erase absorption differences and wavelength shifts.