Fundamentals of calibration transfer through Procrustes analysis

In analytical chemistry, it is necessary to form instrument-dependent calibration models. Problems such as instrument drift, repair, or use of a new instrument create a need for recalibration. Since recalibration can require considerable costs and cause time delays, methods for calibration transfer have been developed. This paper shows that many of these approaches are based on the statistical procedure known as Procrustes analysis (PA). Transfer by PA methods is shown to involve translation (mean-centering), rotation, and stretching of instrument responses. This study investigates the ability of different forms of PA to transfer near-infrared spectra measured on two different instruments. Spectroscopic interpretations of translation, rotation, and stretching are provided. It is found for the data sets investigated that unconstrained forms of PA generally produce better results. It is also shown that translation is the key step for transformation of spectra and may often be all that is required.