Use of NIR spectroscopy and chemometrics for on-line process monitoring of ammonia in Low Methoxylated Amidated pectin production

The development of an on-line process monitoring and control system for the automatic dosing of ammonia for production of Low Methoxylated Amidated (LMA) pectin is described. The system is based on on-line optical fibre Near Infra-Red (NIR) transmittance spectroscopy of the amidation liquid, consisting of ammonia, isopropylic alcohol, water and minor impurities. The focus in this paper is on the chemometric calibration development and validation, and the improvement on the ammonia dosing for the production. Feasibility studies revealed that the calibration for ammonia, based on NIR transmittance spectra (spectral region from 5300 to 11 000 cm −1) is highly temperature dependent in the range −9–20 °C, but careful choice of spectral pre-processing and wavelength selection could eliminate the temperature dependency. Using the first derivative of the NIR spectra and the selection of the spectral region 5423–6658 cm −1, the average Partial Least Squares regression prediction error was reduced to 1.75% of the full range of the initial calibration, as determined from an independently validated data set one full year after initial implementation in the factory.