Comparison of PARAFAC2 and MCR-ALS for resolution of an analytical liquid dilution system

An analytical liquid dilution system is proposed to collect information on the intramolecular distribution of ester groups on the pectin carbohydrate backbone by injecting a solution of pectin into a carrier stream containing a fixed concentration of dye. The dye binds site-specifically to the poly-α-(1→4)-d-galacturonic acid units which are not esterified. The carrier stream is led to a Continuously Stirred Tank Reactor (CSTR). The pectin is slowly diluted while UV–VIS spectra are continuously recorded at the reactor outlet, providing a wavelength-by-time matrix for every sample. Thirty-one pectins, enzymatically deesterified to give different ester distributions, are measured using remethylated lemon pectin as starting material. The combined sample matrices are analysed using multi-sample Multivariate Curve Resolution (MCR) and PARAFAC2, both Alternating Least Squares (ALS) regression algorithms. Both algorithms successfully describe the data giving a lack of fit between 2.0% and 8.3%, depending on the number of components extracted and the choice of constraints applied. The paper discusses how and on which terms the two algorithms can be compared. Interpretable information about the deesterification pattern of the pectin-related species and the extent of deesterification is obtained from the resolved dilution concentration profiles. The most detailed chemical description of the pectin-dye species is obtained with an unconstrained MCR-ALS five-component model.